The objective of this study is to investigate the penetration and perforation resistance of alumina ceramics against kinetic energy projectiles. There are several different mechanisms by which a target can fail when it is subjected to impact of a projectile and these may occur singly or in combinations of two or more. The presence of large number of penetration and failure mechanisms makes the investigation of the perforation very difficult. Because of this difficulty, the analytical investigations of penetration and perforation processes usually assume one type of failure mechanism. One of these analytical investigations is reviewed and it is seen that this analytical model is capable of predicting after impact parameters reasonably accurately. A parallel investigation of this problem is also been carried out numerically by using Autodyn hydrocodes. Numerical study is capable of simulating the main changes in ceramic/steel composite target during penetration process of kinetic energy projectile. Results of analytical and numerical investigations are parallel to each other. A set of experiments was carried out for checking the results of analytical and numerical calculations with the experimental data.

Aircraft disasters during take-off and landing by the impact of foreign object debris (FOD) have always been an important issue. When the wing is lifted, its upper and bottom surfaces are subjected to compressive and tensile stresses, respectively. The bottom surface of the aircraft wing is vulnerable due to the threat of runway debris, which may travel at high speed, leading to the catastrophic failure of structures under tension. This thesis studies the ballistic performance of a structural panel subjected to projectile impact when the influence of in-plane pretension is considered. An experimental program was proposed to obtain the laboratory testing results where a special rig was designed to apply pretension to the panel as it is being hit by a projectile launched from a gas gun at velocities between 60 to 160 m/s. Instrumentation was used to record impact and residual velocities at different stages of the impact process. The panel was supported on opposing sides in one direction with two free sides in the other direction. Two target materials related to aircraft structure were considered, i.e., aluminium alloy, 2014-T6 and carbon fiber reinforced plastic (CFRP). Two projectile nose shapes - including flat and hemisphere - were used to account for the influence of debris on the ballistic performance of the target. Target materials were fully characterized in the experimental program. Finite element (FE) models were established and validated, and were used to simulate the response and damage of the panels in the experiments when the influence of pretension is considered. The damage of aluminium alloy, 2014-T6 was modeled using shear failure criterion with damage evolution. For CFRP, the in-plane damage initiation was modeled using Hashin’s damage criterion with damage evolution in terms of fracture energy. Parametric studies were done for both aluminium alloy 2014-T6 and CFRP panels with various pretensions of up to 50% of the material ultimate strength. It has been shown that the pretension has more profound effect on the ballistic behavior of the CFRP panel in comparison with its influence on the ballistic behavior of aluminium alloy panel. The simplified analyses and the numerical modeling reflect the physical nature of the impact response and damage of aluminium alloy and CFRP target panels. Hashin’s damage model for CFRP needs to be extended from in-plane to out-of-plane in order to include shear failure, which may happen for the flat nose projectile impact.

At the ballistic limit velocity of a soft armor target pack, the impact response has been shown to be decoupled in the thickness direction, with the initial few plies behaving in an inelastic fashion via off-axis failure modes such as transverse shear or diametral compression. Past the initial few layers, the remaining plies dissipate energy via membrane-like responses, which only involve in-plane tensile failure modes of the constituent fibers. Since these initial plies only contribute to energy absorption via inelastic kinetic energy transfer, previous studies have shown that these plies may be replaced with another material with other desirable properties, such as lower manufacturing costs or stab-resistance.<div>However, the methodology of determining these parameters is still largely empirical. Armor panels are typically impacted and the shot outcomes subsequently evaluated in order to achieve a quantitative ballistic performance for the panel. Additionally, the ballistic performance is usually determined with respect to a particular projectile. Several models have been proposed to provide an efficient method of predicting ballistic limit determination, but results are sometimes difficult to translate across different projectile-target pairs.<br></div><div>The main research direction in the first volume looking at soft armor impact failure modes and design optimization is obviously of immediate relevance to this dissertation. We start off with an examination of the different types of failure modes that impact on fibrous armors may yield. Subsequently, building on these concepts, we take a deeper look into how different impact parameters cause different failure modes,and we end with a discussion of how the armor panel may be designed around these different failure modes. Although some rudimentary analytical and modeling efforts have been put forth, the current work places more emphasis heavily on experimental techniques and observations, as is the nature of the work typically produced by our research group.<br></div><div><br></div>

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In this study, novel lamination techniques are introduced for the coating of fabrics in order to enhance their ballistic/needle penetration resistance properties. Pressure sensitive adhesive (PSA) was used to create flexible ballistic composite panels with ultra-high molecular weight polyethylene (UHMWPE) fabric. An increase in processing pressure from 0.1 to 8 MPa significantly improved the ballistic performance against 9 mm FMJ ammunition of UHMWPE composite. The number of layers required to stop the bullet were reduced from 45 to 22 layers after lamination without a significant increase in stiffness. The backface signature (BFS) was reduced from 19.2 mm for the 45 layer neat samples to 11.7 mm for the 25 layer laminated samples pressed at 8 MPa. The second lamination technique used patterned thermoplastic hot film to create flexible UHMWPE composite laminates. Hexagonal patterns were cut through a heat transfer vinyl carrier sheet using a vinyl cutter and was used as a mask between the UHMWPE fabric and hot film during heat treatment in order to have the fabric coated only on those regions. The patterns had a nominal diameter of 27.9 mm with a 1 mm gap between each region. A significant improvement in the ballistic performance of UHMWPE fabric is observed after coating each individual layer with patterned hot film and 25 layers of laminated fabric were sufficient to stop a .357 magnum FMJ ammunition compared to unlaminated neat fabric which required 45 layers to stop the bullet. Patterning of the hot film did not negatively affect the ballistic performance of the composite laminates whilst increasing their flexibility in relation to using plain hot film with no patterning involved. It resulted in a 21% increase in bending angle of the 25 layer samples v and 9.5% reduction in bending length of the single plies which both relate to greater flexibility because a higher bending angle and lower bending length correlates to more flexibility. The same technique of patterning of hot film is used in the lamination of woven cotton fabric to enhance needle penetration resistance properties whilst maintaining the flexibility. Patterns used in this study were either hexagonal or a combination of hexagons and triangles and the nominal diameter ranged from 2.6-13.5 mm. The lamination significantly improved the 25G hypodermic needle penetration resistance of the fabric. By increasing the number of laminated fabric plies from 1 to 2, the needle resistance force increased by up to 150%. However, in comparison to just one layer, the flexibility decreased by about 12% to 26% for two and three layers, respectively. It was observed that reducing the sizes of the patterns improved the flexibility of the samples by up to 30% without compromising the needle penetration resistance. / Thesis / Master of Applied Science (MASc)

Concrete is a widely used product and is an important application throughout industry due to its inexpensive cost and wide range of applications. This work focuses on understanding the behavior of high strength concrete in high strain rate ballistic impact loading scenarios. A finite element analysis was created with the implementation of the Concrete Damage and Plasticity Model 2 (CDPM2) to represent the material behavior. The model’s parameters were calibrated to existing literature and the results were analyzed by a comparison of the impact velocity to residual velocity and a qualitative assessment of the impact crater. The model captured the impact dynamics of the contact between the projectile and the concrete target with defined fracture patterns. Impact velocity and target thickness indicated a relatively linear relationship with the final projectile velocity.

Manufacturing more reliable and lighter body armour using the fabrics with high-performance fibres is the development trend of ballistic protection device. However,increasing the reliability of the body armour normally needs to increase weight. Thisinvestigation aims to develop better ballistic performance of body armour withoutaffecting weight. Inter-yarn friction in quasi-static state in fabrics constructed for bodyarmour is one of the important factors affecting ballistic performance. This researchfocuses on increasing inter-yarn friction by surface modification methods for superiorballistic protection of woven fabrics. Finite element (FE) simulation is employed toanalyse the effects of inter-yarn friction on ballistic performance theoretically. BothAPPCVD and sol-gel methods are used to achieve the purpose of practically increasinginter-yarn friction. Ballistic experiments are conducted to evaluate ballistic performanceof the fabrics with different levels of inter-yarn friction after treatments. Through both numerical and experimental investigation, it is confirmed that increasinginter-yarn friction in quasi-static state can improve ballistic performance of fabrics. Theoverall energy absorption will be increased with the increase of inter-yarn frictionbecause higher inter-yarn friction generates higher resistance to the projectile, makesfabric structure more stable, leads to more involvement of the secondary yarns andincreases both KE and FDE percentages. Moreover, higher levels of inter-yarn frictionwill flatten the trauma and make the fabric response more globalised owing to the lesstransverse deflection ability. However, over high inter-yarn friction is counterproductivebecause of stress concentration on the primary yarns. For the surface modification, one of the aramid yarns, Twaron® yarn and one of theUHMWPE yarns, Dyneema® yarn, and their fabric products are used as the substrates. SEM analyses are used to characterise the morphology changes. Both FTIR and EDXanalyses are conducted to identify the coated substance. Based on coefficients of friction test and yarn pull-out test, the APPCVD treatment and sol-gel treatment have been proved as two effective ways to increase inter-yarn friction and at the same time the tensile properties of the yarns and the weight are almost unaffected. Moreover, sol-gel treatment has been established as an effective method for improvingballistic performance without significant weight increase, where the energy absorption ofthe Dyneema® fabric can be increased by 6.74%, and the trauma depth can be decreased by16.99% for Twaron® fabric panel and by10.73% for Dyneema® fabric panel.

The optimisation of compressor stage aerofoil and fan blade design remains an important area of titanium alloy research and development for aerospace gas turbines. Such research has important implications for critical and sensitive component integrity and efficiency. In particular, a better understanding of how deformation twinning interacts with microstructural features in titanium alloys is required, because such twinning facilitates plastic deformation at a higher strain rate than dislocations. To investigate this behaviour, commercial purity titanium and the titanium alloy Ti–6Al–4V were subjected to ballistic impact testing at room temperature with a high strain rate of 10³s⁻¹. In addition, a detailed analysis was conducted of three manufacturing processes of Ti–6Al–4V (wt. %) that are likely to cause deformation twinning: metallic shot peening, laser shock peening and deep cold rolling. The results presented in this thesis have furthered the understanding of the role of deformation twinning in the plastic deformation of α-phase titanium. Key findings of the research include the characterisation of deformation twinning types and the conditions that favour certain deformation twinning types. From the analysis of the ballistic testing of commercial purity titanium, the first definitive evidence for the existence of {112‾4} twinning as a rare deformation twinning mode at room temperature in coarse-grained commercial purity titanium is presented. In addition, the ballistic testing results of the Ti–6Al–4V alloy highlighted very different deformation twinning characteristics. Commercial purity titanium deformed plastically by a combination of {101‾2} and {112‾1} tensilve twinning and {112‾4} and {112‾2} compression twinning modes. By contrast, the deformation twinning of Ti–6Al–4V was limited to only the {101‾2} and {112‾1} tensile twinning modes. The two tensile deformation twinning types have very different morphologies in equiaxed fine grained Ti–6Al–4V. {112‾1} deformation twins span multiple grain boundaries and {101‾2} deformation twins reorient entire grains to a twinned orientation. This observation provides evidence for whole grain twinning of equiaxed fine grained Ti–6Al–4V by {101‾2} twinning. Grain boundary interactions between various deformation twinning types and alpha phase grain boundaries in commercial purity titanium and Ti–6Al–4V are reported and analysed. In commercial purity titanium {101‾2} as well as other deformation twinning types were observed interacting across alpha phase boundaries and higher angle alpha phase grain boundaries. The analyses of the manufacturing processes of Ti–6Al–4V highlight the very different dislocation and deformation twinning structures in surfaces processed by these techniques. A notable feature of material processed by laser shock peening is the almost complete absence of deformation twinning, contrasting with the frequent observation of extensive deformation twinning observed in the material processed by metallic shot peening and deep cold rolling. Therefore, the findings suggest that there is a strain rate limit above which deformation twinning is suppressed. The implications of this research are that a better understanding of the conditions that that favour certain deformation twinning types or propagation behaviours will enable more accurate plasticity modelling and better alloy design. This is important for the design and the manufacturing of titanium components and the high strain rate deformation to which titanium components in aerospace gas turbines can be subjected because of bird strike, foreign object debris ingestion or fan blade failures.

A Primary objective of the present research is the development of robust CAE (Computer-Aided Engineering)-based approaches for designing armour plates subjected to ballistic impact by small-calibre hardened peojectiles with or without a protective sheath. Amongst the challenges in simulation is the capturing of target plate material behaviour at high strain rates with possibilities of adiabatic heating. A comprehensive numerical study carried out has resulted in the identification of simulation guidelines using a commercially available explicit finite element anlaysis solver (viz. LS_DYNA). The interferences thus drawn in terms of modeling approach 9I.e. shell, solid or axisymmetric or a mixed representation). Mesh density and element type, contact condition, and constitutive model 9I.e. discrete strain-rate based, Cowper-Symonds, or Johnson-Cook) with failure criteria are verifiable and greatly beneficial for armour plate design. Confidence in the suggested procedures has been obtained through extensive correlation of numerical results with experimental residual velocities and ballistic limits as well as projectile and target plate failure modes. A wide range of impact velocities has been considered (from a low velocity of about 5m/s to an ordnance range velocity of 800+ m/s). Target plates made of variants of mild steel and aluminium alloys have been studied. The simulation approaches have been applied to single-layered as well as multi-layered target plates. Although a majority of the comparisons has been made against published test results, a new ballistic impact testing facility has been set up in course of the current research and excellent correlation of numerically predicted residual velocities and failure modes has been obtained against the tests carried out for aluminium plate using the latter facility. A unique feature of the current experimental effort is the capturing of the complete trajectory of projectile beginning with oblique impact through subsequent perforation/ricochet. Furthermore, projectiles of various nose-shapes such as ogival, conical, hemispherical and blunt have been employed. The power of simulation has been demonstrated with the help of a number of parametric studies with variables such as plate thickness and material properties, as well as projectile mass and diameter, and obtaining physically consistent results. Additionally, existing semi empirical models for residual velocity and ballistic limit prediction have been reviewed, and new user-friendly models have been proposed based on energy conservation and predominant shear plugging failure mode of target plate. Finally, the goal of applying the present research work as a design tool can be well-served by packaging the knowledge gathered here in the form of a user-friendly guide with a graphical user interface(GUI). To this end, an application using MS windows VC++ utilities has been created with the functionalities of: (a) viewing reference LS-DYNA input data files for selecting typical problems of impact on steel and aluminium plates; (b) computing complete lists of strain rate-based material quantities required in LS-DYNA material models like discrete strain rate-based, Cowper-Symonds and Johnson-Cook by specifying the minimum number of easily available quasi-static properties (such as elastic modulus, yield and ultimate strengths, etc.), and (c) estimating residual velocities using the semi-empirical relations for steel and aluminium plates derived in the current work.

A interação dinâmica resultante do impacto de esferas de aço contra chapas de alumínio é estudada através da representação numérica de testes experimentais, os quais imitam freqüentes colisões de pequenos fragmentos contra a fuselagem de aeronaves. Importância é dada à modelagem do comportamento visco-plástico do material da chapa, o que conduz à proposição de uma modificação no método de caracterização dinâmica mecânica de material, realizado através de um equipamento denominado Barra de Hopkinson. Adicionalmente, a influência de possíveis erros na seleção de parâmetros de simulação, relacionados ao contato, amortecimento estrutural e principalmente ao material, é discutida através de análises numéricas de sensibilidade. Testes de impacto foram conduzidos de forma a se obter a velocidade balística das chapas. O deslocamento máximo permanente das chapas a baixas velocidades também foi medido. O método de caracterização dinâmica de material proposto é então avaliado pela comparação dos resultados de simulações numéricas frente aos dados experimentais obtidos nos testes de impacto. As predições de deslocamento máximo permanente, para testes sem perfuração da chapa, e de velocidade balística, para testes de perfuração total, indicaram uma boa concordância numérico-experimental, respeitadas as observações realizadas acerca dos parâmetros envolvidos. / Dynamic interaction present on impact of steel spheres against aluminum panels is studied through a numerical model of experimental tests, which reproduce common collisions of small debris against airplane fuselages. This thesis emphasizes the panel-material visco-plastic behaviour modeling, which leads to a modification of the material dynamic characterization method, based on a Split Hopkinson Pressure Bar. Influence of possible errors in some numerical simulations parameters, related to contact, structural damping and material behaviour is also discussed by sensitivity numerical analyses. Impact tests were conducted to obtain the ballistic velocity of the panels. Also, the final maximum plate deformation at low velocities was measured. The proposed dynamic characterization method is explored by comparing the numerical simulation and the impact tests. The predicted maximum impact point displacement, for no perforation cases, and the ballistic velocity, for total perforation tests, present a good numerical-experimental agreement, bearing in mind the observations about the various used parameters.