Modelling Tool for Photonic Crystal Device Issues

Modelling Tool for Photonic Crystal Device Issues Chapter 4 SIMULATION DETAILS OF THE PROJECT In the past 10 years, photonic crystals (PCs) have attracted much scientific and commercial interest. The research and design work for PCs starts from accurate modal analysis of the device. Once the modes are found, structure can be simulated for that particular mode and the results of power spectra can be observed at the detector. In this chapter we will discuss about the modelling tool used for solving various problems related to photonic crystal device mentioned in next chapters. In our work, Opti-FDTD v11.0, a proprietary of Optiwave is used as a simulating tool to fulfill this purpose. 4.1 Introduction to FDTD Opti-FDTD is a user-friendly graphical interface that allows the designing of photonic devices in an efficient manner. It provides accurate computer aided simulations with the proper analysis of results. It is a powerful and highly integrated software package which is based on the finite-difference time-domain (FDTD) method. FDTD technique implies the solution of maxwell equations with finite-difference expressions for the space and time derivatives. FDTD schemes are especially promising for the investigation of PBG structures, as they provide an opportunity of analyzing the spatial distribution of the electromagnetic field in PBG structure. Opti-FDTD enables to design, analyze and test nonlinear photonic components for wave propagation, scattering, reflection, diffraction and other nonlinear phenomenon. The method allows for the effective simulation and analysis of structures with sub-micron details. Such fine scale implies high degree of light confinement and a large refractive ind ex contrast of materials to be used in design. Since FDTD method calculates electric and magnetic field at all points of computational domain, it is required for the domain to be finite. For this purpose, artificial boundaries are inserted in the simulation space. In FDTD perfectly matched layer (PML) acts as a absorbing layer for wave equations. In numerical methods, it truncates the computational regions while simulating problems. 4.2 Design Tools of Opti-FDTD Opti-FDTD is used to design photonic devices, simulate and analyze results. Design tools are available in toolbars and menu options. These tools include waveguide primitives, editing and manipulation tools, and special layout regions. Fig 4.1. Main layout of Opti-FDTD Designer Design tools of Opti-FDTD include designer, simulator and analyzer. 4.2.1 Opti-FDTD Designer This section created the desired layout on a wafer that is saved in a file with the extension .fdt. Opti-FDTD designer is opened from the start menu. This section enables a user to work on multiple layouts of project at the same time. One can store and retrieve projects using .fdt files. In addition to the standard cut, copy, and paste editing functions, we can: Scale elements or groups of elements swap overlapping elements snap elements to a grid of the layout zoom into or out of the project layout link elements together The main elements required to perform simulation of layout design include wafer, waveguide and input field. Wafer is the work area of design in Opti-FDTD. Each layout consists of only one wafer. It is a planar substrate on which we place and design the waveguides and cavities. The option of wafer properties is found in edit menu to modify the length, width and material of the wafer. Light wave propagates in Z-direction i.e. along the horizontal path on the screen. Discretization mesh is formed along the X-direction which corresponds to vertical path on the screen. Wafer is a necessary element for running a simulation. While starting a new project, the default material of wafer is air. Fig 4.2. Wafer coordinate system Waveguides are the building blocks of photonic circuits. Path perpendicular to the waveguide center defines the width of the waveguide. The default waveguide profile is air which can be changed while creating a new design. One can resize, rotate and move waveguides anywhere in the layout. Waveguide changes its color after selection. The orientation and shape of a waveguide can also be changed by dragging start/end handles. Properties of a waveguide can be viewed by double clicking it in the project layout. This opens the dialog box of waveguide properties where user can make required changes. Some major waveguide options provided by software include circular, elliptical and linear waveguides. From user point of view, waveguides can also be created by making some cells off in the photonic structure. Such a waveguide allows propagation of electromagnetic wave with minimum attenuation. The input field is an essential element in design to allow simulation to run. Its position is at an input plane which can be moved throughout the layout. It defines the light that enters the simulated structure. Geometric position of the input field and its orientation can be defined in the input field dialog box. Options available for input fields in the software are modal, gaussian, rectangular and user defined. The concept of input field is purely geometrical. It is a position and direction which defines a plane completely. Multiple input fields can be positioned on multiple input fields simultaneously. In a 2D design, input plane can be horizontal (perpendicular to X-axis) or can be vertical (perpendicular to Z-axis). Input field parameters must be defined carefully. The time domain parameters of input field can be specified as continuous wave or gaussian modulated continuous wave. Both the cases demand an input wavelength for the carrier wave. In Opti-FDTD all dimensions are defined in units of ÃŽ ¼m. Multiple input planes are distinguished with the help of ‘label’ facility provided by the software. Input wave can move in positive or negative direction depending on the option selected in the tab of wave configuration. An enable input field check box selects the input plane to be considered in calculation. Figures below show the placement of vertical and horizontal input plane. Fig 4.3. A vertical input plane for 2-D photonic crystal structure Fig 4.4. A horizontal input plane for 2-D photonic crystal structure Layout design in Opti-FDTD software includes profile designer, initial properties and layout designer. Profile designer define the material properties (refractive index of material) and channel profile. Initial properties set initial simulation domain properties including dimensions and material. Layout designer help to draw the lattice type (rectangular or hexagonal) and define the properties of the structure. 4.2.2 Opti-FDTD Simulator Opti-FDTD provides two types of FDTD simulations 32-bit simulation (performed by 32-bit simulators) 64-bit simulation (performed by 64-bit simulators) Opti-FDTD simulator monitors the progress, while the simulation is running. The simulation results are stored in a file with extension (.fda). After launching a 2-D simulation from Opti-FDTD designer, Opti-FDTD simulator displays the results of 2-D simulation. Fig. 4.5 shows the results of 2-D simulation for the structure shown in Fig. 4.3. Fig 4.5. 2-D simulation results (image map) in Opti-FDTD simulator Opti-FDTD simulator window contains output window and graph window. 4.2.2.1 Graph Window While running a 2-D simulation, a simulation window with several tabs appears. The first tab is the refractive index tab (Refr_Idx). Fig. 4.6 shows the refractive index distribution for the structure in Fig. 4.3. Fig 4.6. Refractive index distribution (image map) with palette Opti-FDTD simulator provides several types of views for graphs that include height plot and image map. Fig. 4.5 shows the image map of simulated field Ey. The height plot of the refractive index distribution of structure is shown in Fig. 4.7. Fig 4.7. Height plot of refractive index distribution 4.2.2.2 Output Window The output window contains notification and error tabs which display notifications regarding the status of simulations or any error that occur during simulation. Opti-FDTD simulator does not show this window by default. It can be accessed from tools menu. Figure below shows an example of output window. Fig 4.8. Output Window Simulation parameters can be accessed in Opti-FDTD_Simulator by selecting simulation > simulation parameters. For changing any of the parameters one should use Opti-FDTD_Designer. These parameters can’t be changed in simulator. Observation points can be used to obtain DFT and FFT transform. Observation line is used to observe power spectrum of the transmitted electromagnetic field. Opti-FDTD simulator provides the facility of PWE (plane wave expansion) solver. Fig 4.9. Simulation parameters dialog box Fig. 4.9. Simulation parameters dialog box The simulator provides tools for post-processing data analysis. Structure below shows the workflow of PBG structure analysis. Waveguide layout designer which provides necessary tools for designing a PBG crystal structure. After designing, PWE band solver simulation parameters are configured and PWE calculation is launched. After calculations results are automatically saved in .PND file and data is used for post-processing analysis. Fig. 4.10. Flow chart of PBG structure analysis The PWE band solver contains two windows including band diagram graph window and processing image window. PWE band solver graph window displays data of each eigen values based on each k-vector. During simulation, data is updated continuously from currently running calculations. Progress of calculations can be seen in the window. After completion of calculations, band diagram can be plotted either as band-gap data graph or line-connected data point graph. Fig. 4.11 shows a PWE band solver graph display for the structure shown in Fig. 4.3. Fig. 4.11. PWE band solver graph window Processing message window consist of notification and error tabs. This window displays textual information related to the activities performed in band solver. It provides notification on the k-vector value, tolerance, iteration number and time and date when results were being observed. Fig. 4.12 shows the notification window for the above-mentioned band solver. Error window displays notifications about processing errors. Fig. 4.12. Processing message window 4.2.3 Opti-FDTD Analyzer Opti-FDTD provides the facility to view power spectrum. Observation points are used for this purpose. To view the spectrum, observation area analysis can be accessed from tools menu. Fig. 4.13 shows the observation area analysis dialog box. Fig. 4.13. Observation area analysis dialog box The flow chart below summarizes the full procedure of designing, simulating and analyzing. Following algorithm is used to generate the flow chart. Create a new project Open Opti-FDTD designer Initialize the project Open waveguide profile designer Define the material Define 2-D channel profile Set up initial properties Create a design Draw a PBG crystal structure Set up the lattice properties Insert input plane Set up the input plane Insert observation lines Observe refractive index distribution Observe the refractive index distribution Set up observation lines Run the simulation Set up the simulation parameters Run 32-bit simulation Fig. 4.14. Flow chart of processing of photonic crystal structure using Opti-FDTD [ Courtesy: Ref. [28] ] Analyze the simulation results Open Opti-FDTD analyzer Observe power spectrum Export results The block diagram illustration of the same is depicted in Fig. 4.15. Fig. 4.15. Opti-FDTD block diagram [ Courtesy: Ref. [28] ] Opti-FDTD analyzer first loads the files and processes it to simulator. Simulator runs the proposed design and exports data to other file formats [30]. Further chapters provide the methodology to improve the performance of photonic crystal biosensors. They also explain the application of such device in the emerging field of DNA photonics. A comparative account is also prepared between the performances of photonic crystal biosensor and surface plasmon resonance biosensor which proves the superiority of PC biosensors over SPR devices.

Daily Routines

Your Daily Routines: Then and Now Day| Before College| After College| Sunday| My daily routine before college on a Sunday was to attend church service and was to decide what our Sunday dinner plans were. | My daily routine now that I am enrolled in college on a Sunday are to attend church service, decide what our Sunday dinner plans are, and to make sure that all of my assignments and discussion questions are submitted, and all participation posts are completed for the week. .| Monday| My daily routine before college on Mondays were to go to work and come home to watch my favorite TV shows to wind down from my day. My daily routine now that I am enrolled in college on a Monday is to go to work try to complete a participation post or a discussion question during my lunch break, and then come home and make dinner while studying. | Tuesday| My daily routine before college on Tuesdays were to go to work and come home to watch my favorite TV shows to wind down from my day. | My daily rout ine now that I am enrolled in college on a Tuesday is to go to work try to complete a participation post or a discussion question during my lunch break, and then come home and make dinner while studying. Wednesday| My daily routine before college on Wednesdays go to work and come home to watch my favorite TV shows to wind down from my day. | My daily routine now that I am enrolled in college on a Wednesday is to go to work try to complete a participation post or a discussion question during my lunch break, and then come home and make dinner while studying. | Thursday| My daily routine before college on Thursdays were go to work and come home to watch my favorite TV shows to wind down from my day. My daily routine now that I am enrolled in college on a Thursday is to go to work try to complete a participation post or a discussion question during my lunch break, and then come home and make dinner while studying. | Friday| My daily routine before college on Fridays were go to work and come and decide what our weekend plans were with our friends are and maybe have a date night. | My daily routine now that I am enrolled in college on a Friday is to go to work try to complete a participation post or a discussion question during my lunch break, and then come home to spend time with my husband. Saturday| My daily routine before college on a Saturday was to sleep in late, make a nice lunch fore my husband and then go out with friends and enjoy each others company later that night. | My daily routine now that I am enrolled in college on a Saturay is to wake up a bit earlier than usual to try to complete a participation post or a discussion question before cleaning my house and going out with friends. | What are the major differences in your daily routine now that you are in school? The major differnces that I see now that I am back in school are that I have a more structured schedule and am able to focus on completeing assignments before doing extracuricular activities. Have you included enough time into your schedule for academics? What information in the chart demonstrates evidence to support your answer? I have included enought time into my schedule for academics by cutting out alot of television watching and minimizing the activites I do with friends prior to completeing my class work. The information on the chart that demonstrates evidence of this is there not being any extra activites or television watching during the week or prior to completeing assignments. Do you have an effective balance in the use of your time and your priorities? Why or why not? I do feel that I have an effective balance in the use of my time and my priorities by my cutting out the things that will not assist me in acgieving my goal of and education and earning my diploma. I have substituted watching television by watching the web tutorials. What are some time management strategies you have learned this week that you can implement to make your daily routine effective? A time management strategy I have learned this week is to learn to comprimise with myself I have to buckle down and do my works on certain days so that I can reward myself and be afforded the time for fun activities on other days when my classwork has been completed.

Use of sandwich structures - Free Essay Example

Sample details Pages: 27 Words: 8221 Downloads: 6 Date added: 2017/06/26 Category Statistics Essay Did you like this example? CHAPTER 1 INTRODUCTION 1.1 Introduction The use of sandwich structures has been increasing in recent years because of their lightweight and high stiffness. Commonly, the naval industry and transportation uses the E-glass fibers while the aerospace industry uses composite structures such as carbon fiber. The use of sandwich panels with composite facesheet in the naval industry is particularly appealing because they have better corrosion and environmental resistance and reduced magnetic signatures when compared to double-hull construction steel ships. Don’t waste time! Our writers will create an original "Use of sandwich structures" essay for you Create order On the other hand, composite sandwich panels are easily susceptible to damage by a strange object impact. The damage may be visible, penetration or perforation, or invisible, internal delamination and debonding. Both types of damages will result in stiffness and strength reduction. It is then important to study the impact behavior of composite sandwich panels. Failure in composite structures can be caused by low, high and extremely high or localized impact. An impact caused by a foreign body initiates two waves from impact point in a panel: a through-thickness wave and a transverse shear wave. Whether or not these waves play an important role in the impact response of the panel depends on the actual contact duration between the projectile and panel and the time it takes the transverse shear wave to reach the panel boundary. Figures 1.1 (a)-(c) show three-impact scenarios: low-velocity, high-velocity and ballistic impact. In low-velocity impact, the contact force duration is long compared to the time it takes the transverse shear wave travel to reach the plate boundary. Many waves reflect back and forth across the side dimension of the panel. In high-velocity impact, the contact force duration is much shorter than the transverse shear wave travel time through the panel. Usually high-velocity impact is the same with perforation and localized damage of the panel. Ballistic impact deals only with through-thickness wave propagation. During ballistic impact, there is complete perforation of the panel with little or no panel deformation. The contact force duration is approximately the wave travel time through the panel thickness. Ballistic impact usually involves the study of penetration mechanics. Low-velocity High-velocity Ballistic Impact The projectile to panel mass ratio will control whether wave propagation effect dominates the panel impact response and then suggested that a mass ratio be use as a parameter to determine impact response. It was shown that small mass impacts produce more damage than high-mass impacts having same kinetic energy. While small-mass impacts were defined by wave-controlled response, large mass impacts were defined by boundary-controlled response. Common examples of low-velocity impact are of bird strikes, collision with floating object, and dropped tools, may cause damage. Underwater blast or debris from a faraway explosion and air was considered as a high-velocity impact situation. Examples of ballistic impact would be a bullet or fragments from a nearby explosion hitting the panel. Another important factor governing the impact on composite structures is the ballistic limit. The ballistic limit is defined as the highest velocity of the projectile to cause perforation. When the residual velocity (exit) of the projectile is zero, then the initial velocity of the projectile that causes perforation is the ballistic limit of the sandwich panel. The ballistic limit may be calculate analytically or determined experimentally. In the experimental method, sandwich panels are shoot with projectiles over narrow range of velocities to either just cause penetration or to just perforate the panel. There exists a striking velocity at which 50% of the panels are completely perforate above this value and remaining 50% are partly penetrate below this value. This striking velocity is expresse as V50, which is the ballistic limit of the panel. In the analytical approach, the ballistic limit is determined by the conservation of energy principle. The approach is complex because it inc ludes a variety of factors like core thickness, facesheet thickness, shape of the projectile, core crushing stress, and so on. 1.2 Problem Statement This topic was an expansion of the Wan Awis research. He has done only an experimental work. For impact application, we need to predict skin and core material thickness. Since impact phenomena depend on numerous parameters such as material properties or projectile geometry, a numerical model, validated experimentally, is necessary to allow the study of the influence of several parameters without making costly experimental tests. This will definitely enhance the development of our military technology and achievements in the future because of the ability of this software to cut production cost and time consuming of the experimental work. The numerical figures have been compared to modal test results aiming mainly to validate the studies. Simulation based on finite element analysis (FEA) must not exceed 15% error or this simulation could be claimed not acceptable. 1.3 Objective To simulate the damage of composite sandwich structures subjected to high-velocity impact using finite element analysis. To determine the energy absorption capability of the components on the behavior of the sandwich panel under impact load using ANSYS AUTODYN 13.0 To validate a numerical model with actual experiment. 1.4 Scope of Works To characterize a mechanical behavior of carbon fiber panel by using tensile and determine the fiber volume force and density. Design and validate the numerical model. Conduct a ballistic impact test simulation. Using the experiments data to calculate the energy absorption on the impact. CHAPTER 2 LITERATURE REVIEW 2.1Introduction A great deal of research has been conducted in the area of impact of composite structures. In this chapter, previous work done on the impact response of laminated composite plates and composite sandwich panels will be reviewed. 2.2Impact of Composite Laminates A detail study of impact of composite laminates in the three impact regimes ballistic impact, low-velocity and high-velocity is presented in this section. 2.2.1Low-velocity Impact Abrate, 1998 give a specific review on different analytical models of impact on composite laminates. He classified impact models into four groups: impact on infinite plate model, energy balance models, spring-mass models, and complete models. In the energy balance model, the initial kinetic energy of the projectile is used to calculate the deformation of the composite laminate. The velocity of the projectile reaches zero at the maximum deflection of the composite laminate. At this point, all of the kinetic energy of the projectile is converted to strain energy needed to deform the composite laminate. Energy balance model assumes that the structure behaves in quasi-static manner. The time history of force and deflection are obtained using the spring-mass model representing the composite laminate. The model shown in Figure 2.1 consists of nonlinear contact stiffness (K), one spring representing the linear stiffness of the structure (Kbs), another spring for the nonlinear membrane stiff ness (Km), effective mass of the structure (M2) as well as the mass of the projectile (M1). Equations of motion are written from a free body diagram. The infinite plate model is used when the deformation wavefront has not reached the boundary but if the wave reaches the plate boundary then this model is not an appropriate one to use. In the complete model, the dynamics of the structure and projectile are taken into explanation. Appropriate plate theory has to be selected and used. In many cases the classical plate theory can be used but when transverse shear deformations become significant, higher-order theories must be used. One of the earliest studies on the impact of composite laminates was by Goldsmith et al, 1995, who conducted high-velocity and quasi-static impact tests on carbon-fiber laminates by using a cylindro-conical projectile. Three different specimen of varying thickness were considered. Energy balance principle was used to predict the dynamic penetration energy, static penetration energy, and also the ballistic limit of the composite laminate. The fiber failure accounted for most of the energy absorbed. The predicted theoretical energy was in good agreement with measured energy for thin laminates but not for the thick laminates. This was approved to the fact that transverse shear deformation played an important responsibility in thick laminates subjected to low-velocity impact. The effect of transverse shear deformation was not dominant due to its quick occurrence in the high-velocity impact of laminates. Therefore, the predicted energy in the dynamic case was always close to but less than the measured energy for the thin and thick laminates. The predicted ballistic limit was less than measured values due to the nonlinear factors. Cantwell, 2007 studied the influence of target geometry in the low-velocity impact of composite laminate. The tests were performed on GFRP plates with hemispherical indenter on either circular or square supports. He used energy-balance model to predict the plate deflection and the delamination area of the laminated structure. His study stated that there is little or no influence of target geometry on the failure modes. It also suggested that delamination was dependent on interlaminar shear stress and increasing the plate diameter required more energy for damage initiation. Hou et al., 2000 predicted impact damage in composite laminates using LSDYNA 3D. The numerical results were compared to experimental results on low-velocity impact on composite laminate with an initial velocity of 7.08 m/s The Chang-Chang failure criteria was modified taking the shear stress into consideration and the model was implemented in DYNA 3D. 2.2.2 High-velocity Impact In 1988, Cantwell performed high-velocity impact tests of CFRP laminates with 6 mm diameter, 1g steel ball as the projectile. The influence of fiber stacking sequence and target geometry was study. The experiments reveal that varying the target geometry had no significance on initial damage caused. While the damage initiated in the distal facesheet in thin laminates, however, in thick laminates it initiated from incident facesheet. Zhao et al., 2007 investigated the failure modes in composite laminates subjected to high-velocity impact. Three different laminates were subject to impact by hemispherical projectile in the range of 10-300 m/s. An energy balance was considered and equations for residual velocity for the laminates were given in terms of the mass of the projectile and striking velocity. The thickness and stacking sequence were finding to play an important role in the energy absorption. Cheng et al., 2007 developed an analytical model based on the spring-mass model for high-velocity impact of a blunt ended and a sharp-ended projectile on thick composite laminates. They considered the effect of moving boundary due to the propagation of shear wave. The analysis was modeled using series of quasi-static events. At the end of each quasi-static step, the failed layers were remove based on punch shear damage and fiber damage criteria, and the wave front was moved outwards. While the first spring stiffness constant was measure based on the penetration depth of the projectile, the second spring stiffness constant was measured based on the bottom node of the plate. 2.2.3 Ballistic Impact Silva et al., 2005 performed numerical simulations of ballistic impact on thin Kevlar 29 composite laminates using a fragment-simulating projectile. The laminate material model was simulating using AUTODYN and the projectile was modeled using Johnson-Cook strength model. Finite element mesh for both laminate and projectile was generating using True Grid. Accurate predictions of ballistic limit (V50) and the failure modes were made. Ballistic limit is the minimum velocity of impact at which a given projectile just perforates a given target. On occasion, the term is also used to identify the maximum impact velocity at which the projectile can penetrate into the target with perforation. It is often defined statistically as the impact velocity for which the projectile has a 50% probability of perforating the target; it is then denoted by V50. Guild et al., 2007 conducted numerical simulations of ballistic impact on composite laminates and compared them with experimental results. The laminates were made of E-glass/vinyl ester resin with varying thickness and ball bearings of varying mass were use as projectiles. The damage modes included fiber failure, matrix failure, penetration, and delamination. Hashin failure criteria was use to determine the damage mode. Delamination was modeled using an interface between the two plies. As the force increased between two nodes above the specified value, the nodes were untied and the delamination increased. The ballistic limit from experiments was in good agreement with numerical results Naik et al., 2008 studied the ballistic impact behavior of thick composites. E-glass/epoxy laminates of varying thickness were subject to high-velocity impact. The effects of projectile diameter, projectile mass and laminate thickness on the ballistic limit were studied. Wave theory and an energy balance were use to predict the ballistic limit of the laminate. The contact duration of the projectile with the laminate was maximum when the initial velocity was equal to ballistic limit and decreased when the initial velocity increased beyond the ballistic limit. Deka et al., 2008 conducted ballisitic impact on E-glass/polypropylene composite laminates with cylinder-shaped projectiles. The experimental results were validating with numerical analysis using LS-DYNA. Although the laminate was modeling in Hypermesh, LS-DYNA was used to analyze failure mechanisms. The analytical model was base on energy conservation and failure in the numerical analysis was predicted based on Hashins failure criteria. 2.3 Impact of Composite Sandwich Panels In this section, a detail study of impact of composite sandwich panels in the three impact regimes low-velocity, high-velocity and ballistic impact is presented. 2.3.1 Low-velocity Impact Mines et al., 1998 investigated quasi-static loading and low-velocity impact behavior on two different composite sandwich panels. While the first panel was made up of E-glass/vinyl ester skin and Coremat core, the second panel was made of Eglass/epoxy skin and aluminium honeycomb core. The first panel with Coremat core had failed in the sequence of core shear, debonding, and distal facesheet damage and incident facesheet failure. The second panel failed by core shear, debonding, incident facesheet failure and then distal facesheet failure later. In the low-velocity impact tests, the failure pattern remained the same in both the panels as of the quasi-static tests. The core properties and impact velocity govern the energy absorption capability of the sandwich panel. Wen et al., 1998 investigated the penetration and perforation of composite laminates and sandwich panels under quasi-static, drop-weight and ballistic impact tests by flat-faced, hemispherical-ended and conical-nosed indenters/projectiles. They categorized the impact on laminates and sandwich panels into low-velocity impact and wave-dominated (high-velocity/ballistic impact) response. It was also stated in the research that sandwich panels subjected to low-velocity impact have similar load-displacement characteristics as of quasi-static loading case. The perforation energy required by flat faced projectile was more than hemispherical-ended and conical shaped projectiles in high-velocity impact. Schubel et al., 2005 investigated quasi-static and low-velocity impact behavior of sandwich panels with woven carbon/epoxy facesheets and PVC foam. The low-velocity impact model behaved similar to quasi-static loading case when loads and strain levels were same. The static indentation response was compared to the numerical results obtained using ABAQUS and were in good agreement. A membrane solution, assuming membrane in the core affected region and plate on elastic foundation in the rest of sandwich panel was in poor agreement with the numerical results. Hoo Fatt et al., 2001, developed static and dynamic models of sandwich panels subjected to low-velocity impact. They investigated the behavior of sandwich panels having carbon/epoxy skins and a Nomex honeycomb core with a hemispherical indenter under various support conditions such as simply supported, fully clamped, and rigidly supported. Spring-mass models were considered to determine the load-displacement curve. They also investigated the damage initiation of sandwich panels under low-velocity impact loading. The initial mode of damage depended upon the panel support conditions, projectile nose shape, geometry of the specimens, and material properties of the facesheet and core. Various failure patterns were studied and solutions based on them were derived separately. The analytical solution for the ballistic limit was also found and results for thick laminates were in better agreement than thin laminates. Suvorov et al., 2005 performed numerical analysis on sandwich panels with foam core and studied the effect of interlayer in between the top facesheet and foam core. The foam core was modeled as crushable foam in ABAQUS. While the polyurethane (PUR) interlayer reduced the deformations in both the core and the composite facesheets, the elastomeric foam (EF) interlayer offered a better protection for the foam core alone. Besant et al., 2001 performed numerical analysis on sandwich panels with aluminium honeycomb core. The metal honeycomb core was modeled as elastic perfectly plastic material. A quadratic yield criterion was proposed for the core material, which included both normal and transverse shear stresses. The importance of core plasticity in finite element analysis was explained. 2.3.2 High-velocity Impact A great deal of work has been done in the area of low-velocity impact of laminates and sandwich panels and high-velocity impact of laminates but limited work has been presented in the domain of high-velocity and ballistic impact of sandwich panels. The following describes some recent studies on the high-velocity impact of composite sandwich panels Velmurugan et al., 2006 studied the projectile impact on composite sandwich panels in the range of 30-100 m/s. The sandwich models in this study were not the typical sandwich panels in the conventional sense. They had a core height comparable to the facesheet thickness and acted as a bonding agent between the facesheets. Energy-balance model was used to determine the ballistic limit of three different sandwich panels. They assumed the sandwich panel as a single plate since the foam layer was thin and comparable to facesheet thickness. Also uniform failure mechanism along the through thickness direction was assumed in their model. Skvortsov et al., 2003 developed an analytical model using energy-balance principle to determine the ballistic limit of composite sandwich panels subjected to high velocity impact. Two different sandwich panels were subjected to high velocity impact using three different projectiles. These tests were conducted on simply supported and rigidly supported boundary conditions, and the initial velocity was varied in the range of 70-95 m/s. The predicted panel energy was close to the experimental values and the error was due to the strain-rate effects, plastic behavior, and hardening phenomena, which are not consider in the analysis. 2.3.3 Ballistic Impact Kepler et al., 2007 conducted ballistic impact on sandwich panels consisting of GFRP plates and Divinycell H80 core, with three different projectiles. Lumped spring mass model was use to calculate force histories and panel response. Concentric rings connected by shear springs represented the sandwich panel. In this model, core shear deformation was assumed as the single significant contributor to the sandwich panel stiffness. The facesheet orthotropic was neglected in the panel response. Four different force histories: constant force, triangular force, sine series, and combination of sine and triangular force were used to calculate the energy loss in the panel. Of these, triangular and combined force gave results in better agreement with experimental results. 2.4Aluminium Honeycomb For design and construction of lightweight transportation systems such as satellites, aircraft, high-speed trains and fast ferries, structural weight saving is one of the major considerations. To meet this requirement, sandwich construction is frequently use instead of increasing material thickness. This type of construction consists of thin two facing layers separated by a core material. Potential materials for sandwich facings are aluminium alloys, high tensile steels, titanium, and composites depending on the specific mission requirement. Several types of core shapes and core material are been applied to the construction of sandwich structures. Among them, the honeycomb core that consists of very thin foils in the form of hexagonal cells perpendicular to the facings is the most popular. A sandwich construction provides excellent structural efficiency, i.e., with high ratio of strength to weight. Other advantages offered by sandwich construction are elimination of welding, superior insulating qualities and design versatility. Even if the concept of sandwich construction is not very new, it has primarily been adopt for non-strength part of structures in the last decade. This is because there are a variety of problem areas to be overcome when the sandwich construction is applied to design of dynamically loaded structures. Other investigators have previously carried out noteworthy theoretical and experimental studies on linear elastic and nonlinear behavior of aluminium sandwich panels. Kelsey et al., 1985 derived simple theoretical expressions of the shear modulus of honeycomb sandwich cores. Witherell, 1977 performed an extensive theoretical study for structural design of an air cushion vehicle hull structure using aluminium honeycomb sandwich panels. Okuto et al., 1991 showed the validity of the so-called equivalent plate thickness method in which a honeycomb sandwich panel subjected to inplane loads is approximately replaced by a single skin panel with equivalent plate thickness. Kobayashi et al., 1994, studied Elasto plastic bending behavior of sandwich panels. An experimental study was undertaken by Yeh et al., 1991 to investigate the buckling strength characteristics of aluminium honeycomb sandwich panels in axial compression. Kunimo et al., 1989 both, have studied the characteristics of the energy absorption capacity of bare honeycomb cores under lateral crushing loads theoretically and experimentally. 2.5 Ballistic Limit The ballistic limit may also be defined as the maximum velocity at which a particular projectile is expected to consistently fail to penetrate armor of given thickness and physical properties at a specified angle of obliquity. Because of the expense of firing tests and the impossibility of controlling striking velocity precisely, plus the existence of a zone of mixed results in which a projectile may completely penetrate or only partially penetrate under apparently identical conditions, statistical approaches are necessary, based upon limited firings. Certain approaches lead to approximation of the V50 Point, that is, the velocity at which complete penetration and incomplete penetration are equally likely to occur. Other methods attempt to approximate the V0 Point, that is, the maximum velocity at which no complete penetration will occur 2.6 Energy Absorption Mechanism of Composite Materials The research was done by Naik and Shrirao at 2004. Impact loads can be categorized into three categories which is low-velocity impact, high-velocity impact and hyper-velocity impact. This classification is made because of change in projectiles velocity will result in different mechanisms in terms of energy transfer between projectile and target, energy dissipation and damage propagation mechanism. Basically, ballistic impact is considered as low-mass high velocity impact. In this impact event, a low-mass projectile is launched by source into target at high velocity. It is unlike low-velocity impact that involved high-mass impactor impacting a target at low velocity. In view of the fact that ballistic impact is high velocity event, the effect is localized and near to impact location. According to Naik et al. (2006), seven possible energy absorbing mechanisms occur at the target during ballistic impact. Those mechanisms are cone formation at the back face of the target, deformation of secondary yarns, tension in primary yarns/fibres, delamination, matrix cracking, shear plugging and friction between the projectile and the target. Then, the researchers formulated all these energies into equation whereby the total energy absorbed by the target is summation of kinetic energy of moving cone EKE, shear plugging ESP, deformation of secondary yarns ED, tensile failure of primary yarns ETF, delamination EDL, matrix cracking EMC and friction energy EF. ETOTALi = EKEi + ESPi + EDi + ETFi + EDLi + EMCi + EFi Mines et al. (1999) identified three modes of energy absorption when analysed the ballistic perforation of composites with different shape of projectile. These energy absorptions are local perforation, delamination and friction between the missile and the target. However, the contribution of friction between the missile and the target in energy absorption is low compared to the other two. In terms of local perforation, three through-thickness regimes can be identified, namely: I shear failure, II tensile failure and III tensile failure and delamination. Out of these three regimes, the through-thickness perforation failure is dominated by shear failure. Similar observation has been made by other researcher for thick graphite epoxy laminates whereby the perforation failure is dominated by shear failure. The third main energy absorption mechanism is delamination. Delamination can propagate under Mode I (tensile) and Mode II (shear) loading and each mode can dominate each other depen ding on structural configuration of the composite as well as material properties. Therefore, it can be predicted that the total perforation energy is a summation of energy absorption due to local perforation, delamination and friction between the missile and the target. Epred = Ef + Esh + Edl where Ef = friction between the missile and the target; Esh = local perforation; Edl = delamination Apart from that, Morye et al. (2000) has studied energy absorption mechanism in thermoplastic fibre reinforced composites through experimental and analytical prediction. They considered three mechanisms that involved in absorbing energy by composite materials upon ballistic impact. The three energy absorption mechanisms are tensile failure of primary yarns, elastic deformation of secondary yarns and the third mechanism is kinetic energy of cone formed at back face of composite materials. They concluded that kinetic energy of the moving cone had a dominant effect as energy absorption mechanism for composite materials. However, they neglected a delamination as one of the factor contributed to the failure of composite materials during ballistic impact. 2.7 Kinetic Energy Equation Kinetic energy (KE) attack is a penetration of the residual energy of a projectile. A projectile can give a certain amount of energy to attack and damage a vehicle if the projectile sufficient residual energy when it arrive at the target. This residual is very important to overmatch the capability and strength of the target material to resist penetration, and then it will penetrate. Kinetic energy shot can be presented with the simple law of physic. K.E = Mprojectile Vprojectile2 Increasing the mass (Mprojectile) of the shot increases its energy, but the real payoff comes from increasing its velocity (Vprojectile). If the diameter of the shot fills the whole gun barrel, the projectile becomes heavier and difficult to accelerate to required velocity with the length of the barrel. Additionally, a large diameter solid shot will provide more energy to penetrate the armour plate compared to a projectile which has the same mass but a smaller diameter. Consequently, the larger shot is not only less effective at the target but it is difficult to give it the necessary velocity. According to Chang et al., 1990, depth of penetration at the target will depend not only on residual energy, but also on shape and size of the projectile. The curve shape at the projectile head is more important, as it must not only able to pierce the armour but the shoulders of the shot must also support the remainder so that it does not break up on its way through the armour. If for given mass the diameter of the shot is reduced and is length increased, then for the same residual energy the shot will penetrate further, as it is working on a smaller cross section area of armour. The ratio of length-to-diameter is called slenderness ratio. Any projectile with ratio in excess of 7:1 cannot be spin stabilized it is not until they reach a ratio approximately 20:1 that they can call long rod. So, based on those discussions above, we can conclude that energy absorption can be performed by this relation Eabsor = Ein Eout = [ Mprojectile Vin2] [ Mprojectile Vout2] = Mprojectile (Vin2 Vout2) So, Eabsorbed = Mprojectile (Vin2 Vout2) 2.8 Tsai-Hill Failure Criterion Hill, 1950 proposed a yield criterion for orthotropic materials: G+H12+F+H22+F+G32-2H12-2G13-2F23+2L232+2M132+2N122=1 This orthotropic yield criterion will be used as an orthotropic strength or failure criterion in the spirit of both criteria being limits of linear elastic behavior. Thus, Hills yield stresses F, G, H, L, M and N will be regarded as failure strengths. Hills criterion is an extension of von Mises yield criterion. The von Mises criterion, in turn, can be related to the amount of energy that is used to distort the isotropic body rather than to change its volume. However, distortion cannot be separated from dilatation in orthotropic materials, so Equation 2.8 is not related to distortional energy. Unfortunately, some authors still mistakenly call the criterion of Tsai-Hill a distortional energy failure criterion. The failure strength parameters F, G, H, L, M and N were related to the usual failure strength X, Y, and S for a lamina by Tsai. If only 12 acts on the body, then, because its maximum value is S, 2N=1S2 Similarly, if only 1 acts on the body, then G+H=1X2 And if only 2 acts, then F+H=1Y2 If the strength in the 3-direction is denoted by Z and only 3 acts, then F+G=1Z2 Then, upon combination of Equations (2.10), (2.11) and (2.12), the following relations between F, G, H and X, Y, Z result: 2F=1Y2+1Z2-1X2 2G=1X2+1Z2-1Y2 2H=1X2+1Y2-1Z2 For plane stress in the 1-2 plane of a unidirectional lamina with fibers in the 1-direction, 3 = 13 = 23 = 0. However, from the cross sectional of such a lamina in Figure 2.3, Y = Z from the obvious geometrical symmetry of the material construction. Thus, Equation (2.8) leads to 12X2-12X2+22Y2+122S2=1 as the governing failure criterion in terms of the familiar lamina principal strengths X, Y, and S. And, the appropriate values of Xt or Xc and Yt or Yc must be used depending on the signs of 1, 2, 12 (except that the surface is symmetrical about the plane 12 = 0 because S has only one value). Finally, for the off-axis composite material example of Tsai-Hill failure criterion, substitution of the stress-transformation equations, 1=xcos2 2=xsin2 12=-xsincos In Equation (2.14) yields the Tsai-Hill failure criterion for uniaxial off-axis strength, cos4X2+1S2-1X2cos2sin2+sin4Y2=1X2 which is one criterion. Because a composite lamina usually has different strengths in tension and compression, the values of X and Y must take on the appropriate values depending on the quadrant of stress space consists of four different segments that are continuous in value but not in slope at the uniaxial strengths. The Tsai-Hill failure criterion appears to be much more applicable to failure prediction for this composite material than either the maximum stress criterion or the maximum strain failure criterion. Other less obvious advantages of the Tsai-Hill failure criterion are: The variation of strength with angle of lamina orientation is smooth rather than having cusps that are not seen in experimental results. The strength continuously decreases as grows from 0 rather than the rise in uniaxial strength that is characteristic of both the maximum stress and the maximum strain criteria. The maximum stress and strain criteria are incorrect by 100% at 30. Considerable interaction exists between the failure strengths X, Y, S in the Tsai-Hill failure criterion depends on whether the material being studied is ductile or brittle. Other composite materials might be better treated with the maximum stress or the maximum strain criteria or even some other criterion. 2.9 Finite Element Analysis This subheading starts with a brief introduction to AUTODYN and then follows this with an overview of the SPH implementation carried out. Aizawa et al., 1980 has conducted the research about the AUTODYN software. The AUTODYN software is widely used to simulate non-linear impact phenomena involving large strains and deformations, plasticity, fracture, and flow. The software, available on PCs to supercomputers, is packaged in an interactive, integrated environment wherein the pre- and post-processing and the analysis are contained in a single menu-driven architecture. The software encompasses a number of different numerical approaches for the analysis of impact problems. Within the software, Lagrange, Euler, ALE (Arbitrary Lagrange Euler), Shells, and SPH (Smooth Particle Hydrodynamics) numerical processors (solvers) are available. Impact processes ranging from equipment drop tests to the hypervelocity impact of space debris on a spacecraft can be modeled. Related study also been done by N.K.et al., 1987. The results of a number of analyses are present to highlight the advantages and disadvantages of each numerical technique for different classes of impact applications. It is shown that the selection of the appropriate numerical technique or combination of technique is critical to achieving both an accurate and computationally efficient solution. Impact case studies presented include: Hypervelocity impact of space debris on a shielded spacecraft Impact and penetration of ceramic armor by a steel projectile Oblique impact and ricochet of a steel sphere on RHA armor Impact and crush of a steel girder Explosive formation of an oil well perforator with subsequent impact and penetration on a layered steel/concrete structure The solutions illustrate the use of different numerical techniques with emphasis on efficiency and accuracy. Validation of results with available experimental data is shown. Animations of the numerically simulated impact phenomena can be shown directly from the AUTODYN software. CHAPTER 3 SIMULATION METHODOLOGY This chapter provides the detailed description of method of approach used in carrying out the present study. This includes the strategies that have been design to serve guidelines throughout the process of the study and to assist in achieving the desired objectives. An outline of the methodology is first present in a flow chart to provide an overview of the whole process, followed by detailed discussion of the outline and elaboration of key procedures and techniques employed in the simulations. Flow of my methodology consists the methods that been took in order to accomplish the expected results. Figure 3.1 showed the complete flow of methodology for this research. First thing to do is to make some researches about the topic chosen. All information was gathered through readings from related journals and thesis did some diggings through numerous interviews to get a clear figure about this topic. Next step, study and learn about the simulation program that is going to be used in this research, ANSYS AUTODYN and based on previous researches from literature reviews paper and results, we try to validate whether ANSYS AUTODYN really reliable to be used to continue this research. Then, we simulate in ANSYS AUTODYN. The comparison and analysis were done to validate simulated results with response to actual damage specimen. 3.1Simulation Tools Used Finite element analysis was conduct on the sandwich structure using ANSYS 2-D/3-D finite element model was developed and appropriate material properties were given to each component. For both the cases, ANSYS AUTODYN 2-D/3-D NONLINEAR hydrocode was used. It is an explicit numerical analysis code, where the equations of mass, momentum and energy conservation coupled with materials descriptions are solved. Alternative numerical processors are available and can be selectively used to model different regions of a problem. The currently available processors include Lagrange, Euler, Euler FCT, ALE and SPH. 3.2 Simulation Justification Based on much discussion about which software that are available that could conduct the simulation on sandwich structure subjected to high velocity impact, finally the findings showed that ANSYS AUTODYN is the one that is going to be used to simulate the test. So, to prove that this software is capable to conduct the simulation, some comparison on result between Lagrange solver with SPH solver of ANSYS AUTODYN on one of the literature review topic, Cylinder impacting a rigid wall (Taylor Test) was done. The comparison was on the results for cylindrical shape impact behavior to see whether results simulated with Lagrange solver showed the more or less the same graph as simulate in SPH solver. Figure 3.2 (a) showed the experimental deformation of rigid wall. Whereas Figure 3.2 (b) and (c) represent the resulting final deformations and plastic strain contours for the two analyses. The results which are summarized in Table 3.1 show that both simulations show satisfactory comparison with experiment. The SPH solution compares almost exactly with the Lagrange result. Experimental Deformation Lagrange Simulation Result SPH Simulation Result Table 3.1 Comparison of experimental and numerical Taylor Test results Experiment Lagrange SPH Cylinder Length (mm) 23.13 to 23.59 23.30 23.35 Impact Diameter (mm) 16.70 to 17.04 16.78 16.80 This validation illustrates that the SPH implementation also works well for cylindrical symmetry. It proved that no special unphysical techniques are used to treat particles close to the axis, or indeed anywhere else in the problem. 3.3 Simulation Setup In the numerical simulations presented, the projectile is made of steel. The steel material properties are from the AUTODYN material library and are shown in Table 3.2. The size and geometry of the projectile vary with different problems. The projectile was considered rigid. Lagrange solver was applied to the projectile. The laminated composite material was model by Lagrange method. In order to account for contact/penetration behavior between the Lagrange projectile and the Lagrange laminate, the gap interaction logic of AUTODYN has been activated between the Lagrange cells. AUTODYN has a state of art contact logic wherein objects use a small gap to determine if interaction exists. This gap defines a detection zone that exists around each interacting cell face or node. If a node enters the detection zone it is repelled by a force that is a function of the intrusion depth. AUTODYN also features another special function impact/penetration interface to avoid excessive noise on the impact surfaces. This feature is activated in all the simulations presented. The Lagrange solver has been implemented in both 2D and 3D. However, AUTODYN-2D is used here for simplicity and ease of demonstration. The laminated composite specimens for the penetration experiment were rectangular. In the AUTODYN simulations, an equivalent rectangular laminate plate was modeled in 3D analysis. The size of the rectangular laminate is equivalent to the experiment laminate plate The detail flow of simulation is shown in Figure 3.3. 3.4 Description of Model Consider the composite sandwich panel and rigid projectile as shown in Figure 3.4. The dimension of projectile is 23.10 mm in length and had a hemispherical head with 5.56 mm diameter. The effective material properties used in AUTODYN simulations for this material are shown in Table 3.3. The equation of state of the laminate is linear with a bulk modulus of 15.0 GPa. The laminate is treated as a linear elastic material. The sandwich panel consists of thin orthotropic facesheets of thickness h = 3 mm and isotropic crushable polymeric aluminium core of thickness H = 27 mm. 3.5 Failure Theory For a composite laminate, the Tsai-Hill Failure criteria are applied. Then, for the projectile, it is consider as rigid body. 3.6 Geometry Consider the composite sandwich panel shown in Figure 3.4. The core of the sandwich panel and the rigid projectile were created using *Part. The reference node for the rigid projectile was defined at the bottom of the projectile. The mass of the projectile was assigned automatically by the software 3.7 Material Properties Table 3.2 Material properties of steel projectile Properties Value Reference Density (g/cm3) 7.9 Bulk Modulus (GPa) 200 Shear Modulus (GPa) 90 Yield Stress (MPa) 200 Ultimate Strain 0.4 Erosion Strain 3.0 Table 3.3 Material properties of carbon fiber Properties Value E1 (GPa) 68.5 E2 (GPa) 68.5 E3 (GPa) 9 G12 (GPa) 3.7 v12 0.11 Xt (MPa) 860 Xc (MPa) 795 Yt (MPa) 860 Yc (MPa) 795 St (MPa) 98 1 (kg/m3) 1430 f 0.02 c (MPa) 60 Table 3.4 Mechanical properties of aluminium honeycomb core (Boyer et al., 1991) Properties Value Density (kg/m3) 77 Young Modulus (MPa) 69000 Poissons Ratio 0.33 Shear Modulus (MPa) 25000 Shear Strength (MPa) 120 3.8 Analysis Type An ANSYS AUTODYN Dynamic Explicit type analysis was performed for a time period of 0.15 ms. Non-linear geometry was switched on. All the required outputs such as displacements, velocities and stresses were defined in this module. 3.9 Mesh In finite element analysis, it is preferred to create a mesh with the least number of elements to keep analysis time reasonable while still getting accurate results. The facesheets and core were separate to get a very fine mesh towards the center of the sandwich structure. A biased ratio of 8.5 with 75 elements was defined in the first region of the panel and uniform mesh of 30 elements was defined in the second region. The facesheets had 2 elements through the thickness and the core had 25 elements. Both facesheets and core had default hourglass control and default distortion control. 3.10 Contact, Boundary Conditions The fixed boundary condition (transverse and radial velocity equal to zero) is applied on the outer boundary of the laminate. The velocity of the projectile is V0 = 287 m/s. 3.11 Simulation Analysis This simulation was performed using the Lagrange processor with erosion. Another approach available within AUTODYN is the SPH (Smooth Particle Hydrodynamics) solver wherein a gridless Lagrangian technique is used. Figure 3.9 are shown about the running-in-progress in simulation. Another figure of the simulation progress are shown at Appendix B CHAPTER 4 RESULT AND DISCUSSION 4.1Introduction This chapter is the one that showed all the actual experiment results that previous done and simulated results using ANSYS AUTODYN. The simulations that have been do by using Lagrange method. Comparison was done between the results and actual experiment result to see whether simulation results agreed well with the actual penetration done by Wan Awiss experiment. Data for penetration test were presented afterwards. 4.2Actual Penetration/Firing Test Results These are the data sheets of actual test handle by Wan Awis at 600m closed shooting range at STRIDE. Table 4.1 presents a Summary Penetration Test for Round 5.56mm Steel Core, the profile of specimen used and basic criteria for 5.56mm bullet for this penetration test. Results from this lot size of 5.56 mm bullets are shown in Table 4.2. This data will be compared with the simulated results. Table 4.1 Actual firing condition BALLISTIC IMPACT TEST Sample Hard Panel Test weapon 5.56 mm, 9 mm Test Gun Sample Type Sandwich Panel Shooting Distance 10m (honeycomb) and 5m (carbon fiber) Sample Size (mm) 100 x 100 x 3.3 Temperature 29.3C 31C Ammunition Calibre 5.56 45 mm Rel. Humidity 88% -93% Type of Projectile: FMJ (M855) Steel Core Shooting Angle: 0 obliquity Table 4.2 Test result on composite sandwich structure with 5.56 mm Caliber Range Type of specimen Depth of Penetration Entry diameter Exit diameter Entry Velocity Exit Velocity m mm mm mm m/s m/s 5.56mm 20 Composite 33.1 5.5 6.8 287 220.67 4.3 Simulation Results by ANSYS AUTODYN The simulation results were compared with the experimental ones to validate the finite element model. The variables selected to validate the numerical model were the residual velocity, the ballistic limit, and the contact time. The disadvantage of the experimental impact tests is the limited information concerning the development of the projectile during the impact. The experimental tests provided information only about the velocity of the projectile before the impact over the front skin and after the perforation of the back skin. However, the finite element model showed the progression of the projectile while it was crossing through the sandwich plate. Fig. 4.6 shows the progression of the projectile velocity during the impact (Vimp = 287 m/s). There are some pictures to show the results for this observation on penetration effect on specimen using ANSYS AUTODYN. The pictures was attached at the Appendix B. Simulation impact observations were done on projectiles back view, projectiles front view, and projectiles side view. The simulated results produced by ANSYS AUTODYN were done regarding difference parameters and values against time. The simulated results were presented in form of graph related to parameters specified. 4.3.1Residual Velocity The progress of the velocity shown in Figure 4.6 is representative of each impact. Plotted graphs were extracted from the same node in this simulated analysis. There are three different trends corresponding to the three components of the sandwich (front skin, core, and back skin). In the first region, the composite front skin caused a sudden drop in velocity at the beginning of the impact event, so that the projectile reached the honeycomb core at a velocity of nearly 250 m/s. Secondly, the velocity remained almost constant as the projectile went through the honeycomb core, when the projectile reached the back skin, its velocity was nearly 240 m/s. In the back skin, a new drop in velocity was observed for a residual velocity of over 210 m/s. 4.3.2 Energy Absorbed The projectile lost 46% of its impact kinetic energy, front and back skins absorbed 46% and 41% of the absorbed energy, respectively, and the honeycomb core absorbed 13%. This analysis was made on each numerical test, calculating the energy absorbed by the three components of the sandwich plate. Figure 4.8 specified the relation of absorbed energy against impact velocity. The skins were the main factor responsible for the energy absorption, while the energy absorbed by the honeycomb core was lower. The percentage of the energy absorbed by each component was almost constant for impact velocities higher than 250 m/s: the front skin absorbed 45%, back skin 40%, and core 15% of the absorbed energy by the composite panel (refer Figure 4.7). However, when the impact velocity was near the ballistic limit, the front skin absorbed most of the impact energy so that the projectile reached the back skin at a low-velocity. Thus, the energy absorbed by the back skin was reduced. The energy needed to break high strength carbon-fibres is very high, so the projectile underwent a sudden lost of kinetic energy when it penetrated a composite skin. The main energy-absorption mechanism of the honeycomb core was the plastic strain of the aluminium walls. The experimental tests indicated that the region of the honeycomb over which the projectile impacted had no influence on the results. The energy needed to deform a thin-walled cell of aluminium is very low, so the projectile crossed the honeycomb core with no major loss of kinetic energy. 4.3.3 Depth of Penetration Figure 4.9 shown the graph of displacement against time. The displacement (depth of penetration) is on specimens element that experienced the contact with 5.56 bullet projectile. Relation between those parameters was clearly explained by the above graph (refer Figure 4.9). The depth of penetration is increased by the time of penetration. The maximum displacement is about 3.3 cm which is equivalent to specimens thickness. 4.3.4 Contact Time Another analysis was done to see relation about contact time against the impact velocity (refer Figure 4.10). The contact time was determined as the time between the contact of the projectile with the front skin and the immediate at which the projectile fully penetrated the sandwich plate. 4.4 Velocity (mm/s) Against Time (s) Analysis The value of energy absorb during penetration can be calculated by using this formula Eabsorbed=12MprojectileVin2-Vout2 So, the value for impact velocity for simulated penetration test is 287m/s and value for after impact velocity is around 210 m/s (Figure 4.6) Eabsorbed=120.001782872-2102=34.06J The calculated value of energy absorbed during penetration for the front skin is equivalent with the value in the graph shown. (Figure 4.8) 4.5 Ballistic Limit The ballistic limit was defined as the minimum impact velocity required for the projectile to completely penetrate the sandwich plate. From the model, the ballistic limit calculated was 147 m/s. The experimental ballistic limit estimated was 139 4.2 m/s, by fitting the equation of Lambert et al., 1976 to the residual velocity versus impact velocity curve. A comparison of the results from the numerical model and the experimental test gave a difference of 6% in the ballistic limit. 4.6 Discussions The analysis done were clearly told us some methodology used on findings all required results about penetration test for 5.56 mm bullet projectile to the composite sandwich structure with honeycomb core. The value for each method that was performed based on equation involving simulated result. Table 4.3 contains the comparison between actual and simulation analysis (FEA) regarding the value of residual velocity, and amount of energy absorbed. This table could be highlighted as the final results for this final year degree project on topic Modeling of Sandwich Structure with Honeycomb Core Subjected to High Velocity Impact. Table 4.3 Table of results Data Source Impact velocity (m/s) Residual velocity (m/s) Energy Absorb (J) Actual test 287 220.67 34.06 Simulation Result 287 210 34.58 Percentage of error between results can be calculated using normal method used in many analyses. This percentage error value is very important in order to prove that the simulation software suggested for FEA in this research is reliable to conduct further study on this research in the future. A large difference of error indicates that the simulation doesnt meet it purpose and objective for this research. Error = [(findings actual) / actual] 100% So, based on this formula we can calculate percentage of errors (Eq 4.3) Simulation Results (Residual Velocity) Error = [(210 220.67)] / 220.67 100% = 4.84% Simulation Results (Energy Absorbed) Error = [(34.58- 34.06)] / 34.06 100% = 1.53% The percentage errors calculated were presented in Table 4.4. As we can clearly see, the percentage of error is in an acceptable range. The objectives for this research are relevant and proven scientifically using finite element analysis and engineering methods. Table 4.4 Percentage errors compare to actual penetration test Task Simulation Result (Residual Velocity) Simulation Result (Energy Absorbed) Percentage Error Between Actual Test and Simulation Analysis (%) 4.84 1.53 CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS 5.1 Conclusions In this study the perforation of composite sandwich panels subjected to high-velocity impact was analyzed using a three dimensional finite element model implemented in ANSYS AUTODYN. Experimental impact tests were carried out to validate the numerical model. Good agreement was found between numerical and experimental results; in particular, the numerical simulation was able to predict the energy absorption of the sandwich panel with a difference of 1.53% and the residual velocity of the sandwich panel with a different of 4.84%. The influence of both skins and the core in the energy-absorption capabilities of the sandwich panel was studied in a wide range of impact velocities. Most of the impact energy was absorbed by the skins. For impact velocities above 600 m/s, approximately 45% of the impact energy was absorbed by the front skin and 40% by the back skin. For impact velocities close to ballistic limit, the front skin absorbed almost the 60% of the energy. On the opposite, the honeycomb core absorbed between 10 and 20% of the impact energy by plastic strain, at all the impact velocities analyzed. Also, the energy-absorption mechanisms in both skins and the core were studied. The main mechanism in the skins was fibre breakage whereas in the core the mechanism was the plastic deformation of the aluminium wall. Both in the skins and the core, the damage was concentrated in a small area around the impact point.

Oil Comes from Dinosaurs - Fact or Fiction

The notion that petroleum or crude oil comes from dinosaurs is fiction. Surprised? Oil formed from the remains of marine plants and animals that lived millions of years ago, even before the dinosaurs. The tiny organisms fell to the bottom of the sea. Bacterial decomposition of the plants and animals removed most of the oxygen, nitrogen, phosphorus and sulfur from the matter, leaving behind a sludge made up mainly of carbon and hydrogen. As the oxygen was removed from the detritus, decomposition slowed. Over time the remains became covered by layers upon layers of sand and silt. As the depth of the sediment reached or exceeded 10,000 feet, pressure and heat changed the remaining compounds into the hydrocarbons and other organic compounds that form crude oil and natural gas. The type of petroleum formed by the plankton layer depended largely on how much pressure and heat were applied. Low temperatures (caused by lower pressure) resulted in a thick material, such as asphalt. Higher temperatures produced a lighter petroleum. Ongoing heat could produce gas, though if the temperature exceeded 500 °F, the organic matter was destroyed and neither oil nor gas was produced. Comments Readers shared opinions on the topics: (1)  Victor Ross  says: I was told as a child that oil came from the dinosaurs. I didn’t believe back then. But according to your answer, I’d like to know how the oil in the tar sands of Canada was formed, and the oil in the shale in the USA was formed. Both are above ground, or at least shallow buried. (2)  Lyle  says: Its always been hard for me to believe that such large deposits of oil located so deep below the surface of the earth could come from fossil remains, whether from dinosaurs or plankton. Looks like some scientists are also skeptical. (3)  Rob D  says: I must have been lucky in my educational journey through life, its the first time I’ve heard this silly misconception (not a perception). Oil and gas below landlocked regions? No problem, you just need to be aware of Plate Tectonics and other geological processes; there are fossils of sea creatures near the summit of Everest! Of course some people choose mysticism and superstition to explain these things, which is where the dinosaurs and oil connection possibly originates – from those who lump all (what to them are) â€Å"scientific mysteries† together.Regarding the oil Without fossils; just reading the title of the research paper sheds some light as to where this is going: â€Å"Methane-derived hydrocarbons produced under upper-mantle conditions†. So these guys say no need for fossils to produce oil (i.e. not a fossil fuel), but where does the methane come from? Yes, I’ll give it a read but I’m not hopeful they have overturned established th eory just yet (always remember how the media reports science – they love the controversial and the sensational). (4)  Mark Petersheim  says: I want to know, is there any positive effect of crude oil on the environment? Not long ago we discovered that microbes lived in extreme temperatures near thermal vents on the ocean floor, we never thought this was possible. There must be something that eats crude oil. Some other species must benefit from this bi-product of nature other than humans. Anybody out there have data to support this? (5)  winoceros  says: Certain bacteria digest crude oil. It leaks into the oceans naturally all the time, is â€Å"eaten† or broken down, and used as energy by the bacteria. If it’s got carbon in it, something will figure out how to eat it. (6)  Ed Smithe  says: How is it then that we have found petroleum on Titan (Saturn’s moon), which, as far as we know, has never hosted life? This theory is at best flawed, and at worst, invalid. Obviously there are processes at work that don’t require dinosaurs, or plankton, or other living things to create hydrocarbons. (7)  Chrystal  says: Couldn’t it then be assumed that dinos that fell into the sea or lived in the sea became petroleum in the same manner? (8)  Andre  says: That was my thought too. That dinosaurs could also be the animals that became oil. I’m sure some oil existed before dinosaurs but if the theory is true, how could they not be a contributor at all? (9)  Andre  says: Andre: If oil came from dinosaurs, you would find some form of it around dinosaur fossils. This has never really been the case, and even if it were present it would be in isolated pockets so tiny that recovery would be a waste of time. Diatoms and other life that fell to the ocean floor over a period of millions of years are the only things capable of leaving volumes large enough to extract. (10)  J. Allen  says: What if we wake up one day and find out that the oil we have been pulling from out of the Earth is the glue that is holding the planet together? (11)  Matt  says: Victor Ross†¦Shale is a deep marine sediment. Usually formed in the abyssal plains of the ocean. The only reason it is shallow on land is because of uplift and erosion through millions of years. Tar sands are shallow because its an asphaltic type of hydrocarbon formed in low temperatures, low pressures, and shallow depths. Here in Texas or Oklahoma you can find oil just hundreds of feet below the surface. Sometimes this happens due to microfractures or faults that oil can flow through. Just like water, oil flows from a high to low gradient or is forced up through high formation pressures. Scientists should not be skeptical because oil is a hydrocarbon. It has to come from either living organisms or plant life. It can’t form from anything else. Pressures and temperatures are the deciding factor of what type of oil is formed, if any at all. low temp low pressure asphalt†¦.mod temp mod press oil†¦high temp high pressure gas, extreme pressures and temperatures will completely breakdown the hydrocarbon chains to were it is completely burned off. Methane is the last chain hydrocarbon before it becomes nothing. (12)  Ron  says: I don’t know or really care how the oil and gas got there, but what concerns me is that it is there to act as a cushion between the tectonic plates. Removing it may lead to some very violent earthquakes in coming years. (13)  Luis  says: Back in the 80†²s I was told in elementary school (in MX) that oil comes form dinos. My first question was â€Å"well, how many dinosaurs we need to make an oil deposit of millions of barrels?† Obviously I never believed that hypothesis. (14)  Jeff C  says: The theory of â€Å"fossil fuel† is just a theory. There is no evidence of crude oil/gases beingcreated by decaying creatures or plants. What do we really know? We do know thatTitan has carbon based oil. This has been proven. We do know that the universe hasmultitudes of gases which are carbon based in the absence of plants/animals. The theory of fossil fuel is yet another erroneous conclusion that the lemmings blindly adhere to with little or no objective analysis. (15)  The Truth  says: Oil doesn’t come from living things. All you need to do is study the Russian research since the 1950†²s to figure that out. It is an artificial theory designed to apply the label of limited resource to keep the price artificially high. Dig past the fossil layer? Oil. Dig into bed rock? Oil.Dig under the ocean floor? Oil. Dig in shale? Oil. Time to wake up to reality. (16)  Danny V  says: Wrong! Oil does not come from any living thing. This is a lie that was formed during a convention in Geneva in the late 1800s in order to have us feel that it is very limited and running out. Science has bought into it, just as they have macro-evolution. (17)  danny  says: Jeff, you are absolutely right, especially in your use of the term â€Å"lemmings.† (18)  lore  says: Like other â€Å"created† things (e.g., grass, trees) there are things uniquely â€Å"themselves.† Only God can make a tree. Likely the lubricant of oil on the tectonic plates was placed there like we lubricate an engine to prevent explosive friction. I have personally spoken with two geologists who agree that oil drilling has definitely changed the earths composition causing a sharp rise in earthquakes. When one looks at the process of drilling and fracking its easy to see why earthquakes and tsunamis are a major threat to the earths ruination from mans interference. (19)  youip  says: The oceans died. Natural CO2. Hyper volcanic activity over long periods of time no ice caps. A greenhouse planet full of plant and reptile life. Wonderful conditions for plants. Gargantuan leaves. Apparently plant life was not enough to keep carbon in check in time despite its prosperity. This, unlike our dilemma was a long time coming not a span of a few centuries. Low O2 oceans gave rise to plankton. Whole thing was as a swamp layer from all the death. They sucked out what remained, blocked out life and the vast majority of the oceans, and everything in it died and became acidic. Heat keeps rising, oceans evaporate faster, very acidic rain hits the land and shore lines and soil erosion/land slides/typhoons becomes common. Throw into the mix still active plates and a lot of land life plant and animal found its way to the oceans grave. Oil is a wonderful carbon. All life reduces to carbon. So oil comes from death concentrate and loads of it. Its how the Earth stored its carbon excess as it and its possibly our fate to return to it for dredging it up and releasing it. It’s bittersweet, but its beautifully balanced. Understood or accepted that makes no difference. It does what it does and works how it works. Powerlessness and ignorance are hard truths to swallow yet it goes on despite any preference. Tough luck. (20)  Robin  says: Lets suppose the oil we remove is the buffer that keeps the planet from heating up. Say oil in a pan with heat on it can absorb more heat then the water that displaces the oil because water boils and turns to vapor. Water is put in reservoirs beneath the ground in order for the oil to be pumped out, leaving trillions of gallons of water where there was once oil. Now think what will happen once the oil is gone and the water is put into those areas, Do you think we might get a planet that is heating up? And a planet that heats up cannot be good hence global warming. Experiment for you home dwellers. Put water in a pan and then put oil. What tends to develops when both are set to 220 degrees? Now the core is over 5000 degrees. What is buffering us from that. Water? Dream on. (21)  bob  says: I think it is funny that educated adults can be so stubborn that they will not let go of all the fairy tales and myths they were told as children. Even this new ‘theory’ is just an interim step for baby boomers and older generations who got tricked by clever marketing and are struggling to accept the facts. The facts are that coal, natural gas, oil, and diamonds all come from the same geological processes – carbon under heat and pressure. Varying the heat and pressure produces the different end-products. The only reason they wanted you to believe oil was decomposed dinosaurs (and now, decomposing plankton) is because oil was way too plentiful to justify rising prices. Demand and scarcity are both factors in pricing. A compound that practically gushes up when you poke a hole in the ground would not cost that much. A compound that simple folks believe took millions of years to create from a now-extinct life-form costs more. Don’t even start to investigate how DeBeers creates artificial scarcity for diamonds by paying millions of dollars a year to take cartloads of diamonds out of the market, to maintain prices at scarcity levels. Then they sell this myth of hard-to-extract, rare diamond, even though there is a beach in south Africa where the sand is like 75% diamonds, and the south African government will shoot you for trespassing. (22)  Lore  says: To youip: Im fascinated how you present your dogma here based on the fact that all life is carbon. That is no proof of your theory. There is no proof that the ocean ever â€Å"died† (though as a living organism it is certainly dynamic and adapting, not always well, to surrounding changes) and maybe the myth of changes through your described deaths producing oil are just too far fetched and as Bob said, that reasoning looks suspiciously like fake supply and demand stuff. I will add evolutionary desperation to attempt to rule out and sentient reason for oil being created (As Bob and Robin both eluded to, not meaning to put words in their mouths, but that oil has a purpose). Robin: right on. Bob: thank you.