Effect of aluminum reinforcement on the dynamic fragmentation of SiC ceramics

The threat of small-to-medium caliber armor piercing projectiles requires efficient protections that can be achieved by using bilayered configurations. They consist of a front face made up of a hard material and a back face made up of a ductile material. These solutions are among the most interesting in terms of mass efficiency. To design such bilayered concepts, one needs to understand and model fragmentation of the ceramic during the first microseconds after impact. This cracking pattern may significantly reduce the multi-hit capability of the armor. A new material made of porous silicon carbide infiltrated with aluminum is considered. The presence of an aluminum skeleton may improve the residual strength after impact. The present study deals with a comparison of fragmentation properties of this new material with those of porous silicon carbide. Quasi-static experiments and edge-on-impact tests are performed. The role of aluminum is discussed. An anisotropic damage model coupled with a fragmentation study is used to analyze the experimental observations.     

Ballistic protection performance of curved armor systems with or without debondings/delaminations

In order to discern how pre-existing defects such as single or multiple debondings/delaminations in a curved armor system may affect its ballistic protection performance, two-dimensional axial finite element models were generated using the commercial software ANSYS/Autodyn. The armor systems considered in this investigation are composed of boron carbide front component and Kevlar/epoxy backing component. They are assumed to be perfectly bonded at the interface without defects. The parametric study shows that for the cases considered, the maximum back face deformation of a curved armor system with or without defects is more sensitive to its curvature, material properties of the ceramic front component, and pre-existing defect size and location than the ballistic limit velocity. Additionally, both the ballistic limit velocity and maximum back face deformation are significantly affected by the backing component thickness, front/backing component thickness ratio and the number of delaminations.     

Modeling Stress Responses of Multilayer Capacitors Using Varying Termination Geometries

Environmental regulations and increasingly challenging design objectives have prompted the search for alternative materials in microelectronics. Employing these materials alters the reliability profile and performance characteristics of the electronic components into which they are integrated. This article explores how mechanical stresses impact the reliability of ceramic dielectric bodies of multilayer ceramic capacitors (MLCCs) when the material, shape, and thickness of the MLCC terminations were varied. The termination material, termination geometry, and thickness of the ceramic were varied. Results were obtained using finite element analysis, and a reliability model was developed and validated. A preliminary investigation indicated a relationship between the selection of materials used for capacitor termination and the emergence of cracks. Stresses that occurred when boards were subjected to conditions including cyclic bending, vibrations, temperature cycling, and high-g loading correlated to the appearance of cracks on the bottom of the capacitor in proximity to the termination.     

基于犰狳外壳仿生的SiC-超高分子量聚乙烯柔性防护板的试验测试和有限元模拟

个体防护装甲的发展对提高单兵作战能力具有重要意义,基于仿生研究可以为设计高性能装甲提供新的思路。犰狳外壳由六边形鳞片紧密拼接而成,采用分层结构设计,具有很好的柔性和防护能力。本文借鉴犰狳外壳的几何排列模式,采用SiC陶瓷片模仿硬质壳层,超高分子量聚乙烯(UHMWPE)热压板模仿软质壳层,按1∶1厚度比例设计制备仿生复合鳞片,将仿生鳞片紧密排列后封装制成一种新型柔性复合防弹插板。为了验证该种防弹插板的防弹性能并研究其破坏特征,进行弹道极限V0试验测试,结合有限元模拟分析其抗7.62 mm手枪弹侵彻的能力。结果表明:该柔性防弹插板不仅满足防弹性能要求,且具备较好的柔性,可为今后新型防弹插板的设计和优化提供参考。      

Ballistic-performance optimization of a hybrid carbon-nanotube/E-glass reinforced poly-vinyl-ester-epoxy-matrix composite armor

The material model for a multi-walled carbon nanotube (MWCNT) reinforced poly-vinyl-ester-epoxy matrix composite material (carbon nanotube reinforced composite mats, in the following) developed in our recent work (M. Grujicic et al. submitted), has been used in the present work within a transient non-linear dynamics analysis to carry out design optimization of a hybrid polymer-matrix composite armor for the ballistic performance with respect to the impact by a fragment simulating projectile (FSP). The armor is constructed from E-glass continuous-fiber poly-vinyl-ester-epoxy matrix composite laminas interlaced with the carbon nanotube reinforced composite mats. Different designs of the hybrid armor are obtained by varying the location and the thickness of the carbon nanotube reinforced composite mats. The results obtained indicate that at a fixed thickness of the armor, both the position and the thickness of the carbon nanotube reinforced composite mats affect the ballistic performance of the armor. Specifically, it is found that the best performance of the armor is obtained when thicker carbon nanotube reinforced composite mats are placed near the front armor face, the face which is struck by the projectile. The results obtained are rationalized using an analysis of the elastic wave reflection and transmission behavior at the lamina/met and laminate/air interfaces.     

新型集成装甲对EFP侵彻性能的影响

根据平板装药和陶瓷复合装甲与爆炸成型弹丸（EFP）相互作用的原理，提出了新型集成装甲与EFP作用的计算模型；据此模型进行了EFP残余速度计算，证明了在相同面密度的新型集成装甲和陶瓷复合装甲防护下，EFP的残余速度有明显差异；根据该计算模型可进行集成装甲的优化和EFP的反装甲目标设计。     

弹体侵彻陶瓷/金属复合靶板问题的研究

针对弹体侵彻陶瓷/金属复合靶板的问题,将弹体的墩粗变形、陶瓷面板碎裂及陶瓷锥的形成变化和金属背板的变形结合起来,建立了可变形弹体垂直侵彻陶瓷/金属靶板的理论分析模型。利用大型非线性有限元程序LS-DYNA3D,对平头弹侵彻陶瓷/金属复合靶板的问题进行数值模拟,得到了陶瓷/金属复合靶板受弹体侵彻的变形过程。最后给出了典型位置的位移随时间的变化曲线,理论模型分析结果和数值模拟结果与实验结果进行了对比,吻合很好。说明理论分析模型的正确性和数值模拟结果的可靠性,可以为复合靶板的设计提供有利依据。     

Nonlinear finite element analyses of FRP-reinforced concrete slabs using a new layered composite plate element

A simple and shear-flexible rectangular composite layered plate element and nonlinear finite element analysis procedures are developed in this paper for nonlinear analysis of fiber reinforced plastic (FRP)-reinforced concrete slabs. The composite layered plate element is constructed based on Mindlin–Reissner plate theory and Timoshenko’s composite beam functions, and transverse shear effects and membrane-bending coupling effects are accounted for. Both geometric nonlinearity and material nonlinearity of the materials, which incorporates tension, compression, tension stiffening and cracking of the concrete, are included in the new model. The developed element and the nonlinear finite element analysis procedures are validated by comparing the computed numerical results of numerical examples with those obtained from experimental investigations and from the commercial finite element analysis package ABAQUS. The element is then employed to investigate the nonlinear structural behavior and the cracking progress of a clamped two-way FRP-reinforced concrete slab. The influences of reinforcement with different materials, ratio and layout in tension or compressive regions on structural behavior of the clamped slabs are investigated by parametric studies.     

A finite element solution of acoustic propagation in rigid porous media

This paper deals with the acoustical behaviour of a rigid porous material. A finite element method to compute both the response to an harmonic excitation and the free vibrations of a three‐dimensional finite multilayer system consisting of a free fluid and a rigid porous material is considered. The finite element used is the lowest order face element introduced by Raviart and Thomas, that eliminates the spurious or circulation modes with no physical meaning. For the porous medium a Darcy's like model and the Allard–Champoux model are taken into account. The numerical results show that the finite element method allows us to compute the response curve for the coupled system and the complex eigenfrequencies. Some of them have a small imaginary part but there are also overdamped modes. Copyright © 2004 John Wiley & Sons, Ltd.     

Aluminum foam integral armor: a new dimension in armor design

Closed-cell aluminum foam offers a unique combination of properties such as low density, high stiffness, strength and energy absorption that can be tailored through design of the microstructure. During ballistic impact, the foam exhibits significant non-linear deformation and stress wave attenuation. Composite structural armor panels containing closed-cell aluminum foam are impacted with 20-mm fragment-simulating projectiles (FSP). One-dimensional plane strain finite element analysis (FEA) of stress wave propagation is performed to understand the dynamic response and deformation mechanisms. The FEA results correlate well with the experimental observation that aluminum foam can delay and attenuate stress waves. It is identified that the aluminum foam transmits an insignificant amount of stress pulse before complete densification. The ballistic performance of aluminum foam-based composite integral armor (CIA) is compared with the baseline integral armor of equivalent areal-density by impacting panels with 20-mm FSP. A comparative damage study reveals that the aluminum foam armor has finer ceramic fracture and less volumetric delamination of the composite backing plate as compared to the baseline. The aluminum foam armors also showed less dynamic deflection of the backing plate than the baseline. These attributes of the aluminum foam in integral armor system add a new dimension in the design of lightweight armor for the future armored vehicles.     

Effects of the piezoelectric phase’s geometric properties on effective coefficients of 1–3 piezoelectric composites

The present paper reports the electromechanical coupling coefficients of piezoelectric composite material (PCM) are affected by different geometric properties of piezoelectric phase for 1–3 periodic composites that is made of piezoceramic fibers embedded in a soft non-piezoelectric matrix. Three-dimensional finite element model has been developed to study the three types of geometric models of piezoelectric phase with different volume fraction. Geometric models with circular cylinder, square column and circular cylinder alternated with square column are used to predict the coefficients of the validity via asymptotic homogenization method (AHM) and the numerical approach the finite element method (FEM). Three types of geometric model are built via the finite element software ABAQUS, and the elastic, piezoelectric and dielectric coefficients are evaluated via AHM both FEM. The results indicate that the validity parameters of PCM have the direct relationship with the volume fraction, and geometric shape is essential factor for distribution of Von-Misses when device working. The present work may improve application of 1–3 type PCM and offer useful guidelines to the design of PCM devices.     

Impact response of layered steel–alumina targets

The efficacy of a ceramic in protecting against penetration by high velocity projectiles depends not only on its hardness but also on its resistance to flow after comminution. Here we investigate experimentally the response of a model armor system comprising an alumina tile and two steel face sheets subject to impact by steel spherical projectiles. Complementary experiments are performed on the face sheet materials and the ceramic alone in order to gain insights into the inelastic responses of the constituent materials. A parallel numerical modeling study is performed of the system response with emphasis on the shape of the back face following impact. To this end, we employ the ceramic deformation model developed by Deshpande and Evans and modified here to account for dilatational softening following full comminution. Comparisons between model predictions and experimental measurements demonstrate the important role of granular flow. Preliminary parametric studies further suggest that additional effort is required to understand the transition in mechanical response of a ceramic as it transforms from a monolithic solid to a densely-packed granulated medium.     

Some recent developments in numerical modelling of fracture toughness in brittle matrix composites

Finite element analysis was used to study the fracture toughening of a ceramic by a stress induced dilatant transformation of second phase particles. The finite element method was based on a continuum theory which modelled the composite as subcritical material. Transient crack growth was simulated in the finite element mesh by a nodal release technique. The crack's remote tensile opening load was adjusted to maintain the near-tip energy release rate at the level necessary for crack advance. The transformation zone surrounding the crack developed as the crack propagated through the composite. Resistance curves were computed from the analysis; and the results show that during crack advance maximum toughness is achieved before a steady state is reached. The toughening effect of a crack-bridging ductile phase in a brittle material may be predicted if ligament deformation is characterized. A plastically deforming ligament constrained by surrounding elastic matrix material is modelled using finite elements and the relevant toughness enhancement information extracted. Comparison is made to model experiments as well as to toughness measured for technologically important materials. The results suggest that debonding along the interface between the ligament and the matrix may enhance the toughening effect of a ductile phase.     

Modelling creep behaviour of orthotropic composites by the coincident element method

In this paper, the coincident method proposed previously is applied to model the four-point-bending creep experiments conducted at the Cooperative Research Centre for Advanced Composite Structures (CRC-ACS) on carbon-epoxy composite laminates. A parameter identification methodology is first developed to determine the elastic and viscoelastic material models to be used for a coincident element. Simulations are then conducted to model the flexural creep response of the composite laminates under different loading and temperature conditions. The predicted results are in reasonably good agreement with those obtained by experiments. It is demonstrated that the coincident element method is a relatively simple and useful tool for modelling orthotropic and viscoelastic response of laminated composites by using a finite element package that only supports isotropic viscoelastic material models.     

Stress analysis of axially and thermally loaded discontinuous tile core sandwich with and without adhesive filled core gaps

An analytical study is performed to investigate the stress states in an axially and thermally loaded sandwich structure with a discontinuous ceramic tile core. General and simplified models are developed to determine stresses in the constituents of the sandwich structure with and without adhesive in the gaps between adjacent tiles. A general model that allows local bending of the face sheet and a simplified model which assumes uniform through-thickness stress distribution in the face sheets are developed. It is shown that the normal stress in the face sheet decreases when the gap is filled by adhesive, although the tile stress increases. The analytical model shows that normal and shear stresses at the face/core interface can be reduced by filling the gaps between tiles. Filled gaps also elevate the axial stiffness of the structure. Model results are verified by comparison to a previously developed analytical model and finite element analysis.     

Elastic–plastic response of structural foams subjected to localized static loads

Structural foams are increasingly used in engineering applications where high strength and low weight are important. They are used also as energy absorbers. Sandwich structures are a typical area for application of structural foams (as core materials). In a sandwich structure, the core transfers the transverse forces as shear stresses and supports the face sheets against buckling and wrinkling. The structural foams are notoriously sensitive to failure by the application of localized surface loads. Thus, the proper design requires an understanding of the mechanical response of the foam materials to localized external loads.In this paper, the elastic–plastic behavior of closed-cell cellular foams subjected to point and line loads is investigated both experimentally and numerically. Two types of Divinicell foam (H60 and H100) are studied. A finite element modeling procedure is developed using the ABAQUS package. Both plane and axisymmetric formulations for local indentations by rigid bodies are considered. The plastic behavior is described using the *CRUSHABLE FOAM HARDENING material model. This model is calibrated using experimental curves from uniaxial compression tests. Geometrical non-linearity is also taken into account. Both indentation and unloading phases are modeled. Static indentation tests of foam panels and beams are performed using spherical and cylindrical indentors, respectively. A comparison of indentation response obtained from the numerical analysis and from the tests is carried out. A good agreement between the modeling and the experimental data is achieved. In perspective view, the present investigation can contribute towards the development of a damage tolerance methodology for rigid foams.     

Design of 1-3 piezocomposite hydrophones using finite elementanalysis

The 1-3 piezocomposite material was originally developed because of its perceived good performance under hydrostatic operating conditions. Several constrained-dimensional models for piezocomposite hydrophones have been proposed but were found to lack accuracy when compared with experimental data. In addition, they could not be easily extended to include the effect of ancillary components such as cover plates, on the transducer behavior. In this work a finite element model is used for modelling of 1-3 piezocomposite hydrophones to help overcome these two shortfalls. A finite element model initially developed for modelling of thickness mode operation has been extended to include lateral pressures typical of the hydrostatic environment. The response of the new model has been compared with experiment with satisfactory results, allowing an extensive set of simulations to be presented for comprehensive evaluation of 1-3 piezocomposite design as an actuator or a hydrophone. The best hydrostatic performance was obtained by using a low volume fraction composite of PZT-5H and a soft, compressible polymer, with potential enhancements by the incorporation of stiff cover plates covering the ceramic pillars. It is shown that the aspect ratio of the ceramic pillars should be minimized to maximize stress transfer. Additionally, ceramic pillar shape and distribution do not exert a major influence on the hydrostatic behavior     

Non-linear indentation behavior of foam core sandwich composite materials—A 2D approach

Light weight high performance sandwich composite materials have been used more and more frequently in various load bearing applications in recent decades. However, sandwich materials with thin composite face sheets and a low density foam core are notoriously sensitive to failure by localized external loads. These loads induce significant local deflections of the loaded face sheet into the core of the sandwich composite material, thus causing high stress concentrations. As a result, a complex multiaxial stressed and strained state can be obtained in the area of localized load application. Another important consequence of the highly localized external loads is the formation of a residual dent in the face sheet (a geometrical imperfection) that can reduce significantly the post-indentation load bearing capacity of the sandwich structure.This paper addresses the elastic–plastic response of sandwich composite beams with a foam core to local static loading. The study deals with a 2D configuration, where a sandwich beam is indented by a steel cylinder across the whole width of the specimen. The ABAQUS finite element package is used to model the indentation response of the beams. Both physical and geometrical non-linearities are taken into account. The plastic response of the foam core is modeled by the ¹CRUSHABLE FOAM and the ¹CRUSHABLE FOAM HARDENING option of the ABAQUS code. The purpose of the numerical modeling is to develop correct 2D simulations of the non-linear response in order to further understand the failure modes caused by static indentation. In order to verify the finite element model, indentation tests are performed on sandwich composite beams using a cylindrical indentor. The numerical results show good agreement with experimental test data.     

Finite element analysis of tile-reinforced composite structural armor subjected to bending loads

Composite structural armor (CSA) is a multi-functional structure that provides ballistic protection, stiffness and strength at minimum weight. It consists of a multi-layered architecture of polymer composites, rubber and ceramic tiles, stacked in a precise manner to obtain optimal ballistic performance. In the present work, the finite element method is used to conduct a detailed analysis of the mechanisms of load transfer and deformation of CSA subjected to bending loads. The results from two modeling approaches (three-dimensional and two-dimensional simulations) are compared to assess the accuracy of the computationally efficient two-dimensional model. The calculated deflections and surfaces strains from both models are found to agree very well with experimental results. The stress transfer between the layers is further analyzed using the two-dimensional model and the resulting through-thickness strain and stress distributions are discussed. It is found that the deformation of this multi-layered construction is complex and dependent upon the mechanism of stress transfer between the outer surface layer and the ceramic tiles. The effect on non-linear behavior of the constituent materials is investigated. The gap filled with polymer that separates adjacent ceramic tiles is shown to significantly influence the stiffness and strength of CSA. It is found that the plastic deformation of the resin corresponds to the onset of non-linear structural response.     

Multiobjective design of viscoelastic laminated composite sandwich panels

The optimal design of laminated sandwich panels with viscoelastic core is addressed in this paper, with the objective of simultaneously minimizing weight and material cost and maximizing modal damping. The design variables are the number of layers in the laminated sandwich panel, the layer constituent materials and orientation angles and the viscoelastic layer thickness. The problem is solved using the Direct MultiSearch (DMS) solver for multiobjective optimization problems which does not use any derivatives of the objective functions. A finite element model for sandwich plates with transversely compressible viscoelastic core and anisotropic laminated face layers is used. Trade-off Pareto optimal fronts are obtained and the results are analyzed and discussed.