Key Engineering Materials Vols. 535-536

Abstract: Numerical simulations were carried out wherein 20 mm diameter conical nosed projectiles were hit on Weldox 460 E steel targets of varying span and configuration in order to study the influence on the ballistic limit. The effect of configuration was studied with 12 mm thick monolithic and double layered in contact target (2 × 6 mm) of 500 mm span diameter whereas the influence of target span was investigated by varying the diameter of 12 mm thick monolithic target as 100, 200, 300, 400 and 500 mm. The monolithic targets were found to offer higher ballistic limit than that of the layered in-contact target. The ballistic limit was also found to be affected by the variation in span diameter; its value was found to be 199.5, 213.9, 220.7, 226.08 and 230 m/s for 100, 200, 300, 400 and 500 mm span diameter respectively.

Abstract: Shearing tests and penetration tests were combined to determine the mechanical behavior of a stainless steel metal treated by surface mechanical attrition (SMA). SMAT is a usual treatment to strengthen the hardness of treated surface by severe mechanical strain, which generates also a gradient through the direction of thickness. This paper aimed at investigating the behavior of sheet metals treated by means of SMAT under impact loading. Double shearing tests at high strain rate were performed using Hopkinson bar. The experimental results demonstrated notable strain rate sensitivity and a good ductility without sacrificing the strength. An impact perforation test is also performed using inversed perforation test in order to study its sensibility of failure to the loading rate.

Abstract: This paper presents the experimental results to analyze the strain rate sensitivity of aluminium alloy AA-5052 H34. The experiments were carried out under uniaxial tension as well as compression. Tensile tests were carried out with UTM (Zwick Z-250) in the strain rate range of 10-4 to 10-1 s-1 using standard ASTM specimen with gauge length 50mm. Compression tests were carried out in the strain rate range of 10-4 to 103 s-1 using UTM and Split Hopkinson Pressure Bar. Cylindrical specimens of 10mm diameter and 10mm thickness were used for compression experiments. The material showed negative strain rate sensitivity in strain rate from 10-4 to 1 s-1 but showed positive strain rate sensitivity when strain rate increased to 103 s-1. The material was found to be susceptible to Portevin–Le Chatelier effect.

Abstract: The characterization of a closed-cell aluminum foam with the trade name Alporas is carried out here under compression loading for a nominal cross-head speed of 1 mm/min. Foam samples in the form of cubes are tested in a UTM and the average stress-strain behavior is obtained which clearly displays a plateau strength of approximately 2 MPa. It is noted that the specific energy absorption capacity of the foam can be high despite its low strength which makes it attractive as a material for certain energy-absorbing countermeasures. The mechanical behavior of the present Alporas foam is simulated using cellular (i.e. so-called microstructure-based) and solid element-based finite element models. The efficacy of the cellular approach is shown, perhaps for the first time in published literature, in terms of prediction of both stress-strain response and inclined fold formation during axial crush under compression loading. Keeping in mind future applications under impact loads, limited results are presented when foam samples are subjected to low velocity impact in a drop-weight test set-up.

Abstract: By employing the theoretical model of a rigid sharp-nosed projectile perforating the ductile metallic target plate, the present paper re-analyzes the previously published experimental data of APM2 bullet and its hard steel core perforating aluminum armor plates and high-strength steel plates, respectively. Although the bullet deforms during the perforation, the test confirms that the hard steel core dominates in the perforation but the brass jacket, lead cap and end cap only have limited influence on the ballistics. Therein the perforation model of a rigid sharp-nosed projectile may be conducted to analyze the perforation of APM2 bullet. With increasing the thickness of ductile metallic target plate, the inertia effect of target will arise and obviously affect the terminal ballistics. The inertia effect of target must be considered in the scenario of thick target plate.

Abstract: This paper presents various energy absorbing modes in nano composite laminates when subjected to impact loading. Composite laminates, made of 610 gsm WRM(Woven Roving Mat), are prepared by hand lay-up and compression molding technique.Nano clay is dispersed in epoxy and is used as a matrix. Clay dispersion in epoxy is varied from 1% to 5% by weight. A gas gun set up is used to impact the composite laminates with spherical nose cylindrical projectile of diameter 9.5 mm and mass 7.6g.The laminates are subjected to different velocities, which vary from below ballistic limit to above ballistic limit.The vibration response of the laminate at different impact velocities is studied. A time dependent analytical model is used to predict the projectile energy during penetration, and is used to determine the ballistic limit of the laminate. The ballistic limit obtained from experiment is validated with analytical model and good agreement is found.

Abstract: In this note we discuss the derivation of two-dimensional governing equations of a nonlinear shell made of material containing continuously distributed dislocations.We apply the trough-thethickness integration procedure to a nonlinear shell-like three-dimensional body with dislocations. This procedure gives the exact equilibrium equations with the stress resultant and couple stress tensors. The dual to the surface stress tensors are the surface strain measures which are represented by two surface fields. The first one is the translation vector of the base surface of the shell while the second field is the proper orthogonal tensor expressing rotation of the shell cross-section. Since in the case of solids with dislocations there are no displacement vector field. These fields are interpreted as quantities defined on the nonmaterial base surface of the shell.

Abstract: In this paper, we present a general consistent numerical formulation able to take into account strain rate and thermal effects of the material behavior. A thermomechanical implicit approach for element erosion to model material failure is also presented. The numerical model will be illustrated by applications both from the metal forming and the impact domain. All these physical phenomena have been included in an implicit dynamic oriented object finite element code (implemented at LTAS-MN²L, University of Liège, Belgium) named Metafor [1].

Abstract: In large deformation problems, the contribution of nonlinear terms is quite significant. Hence, components/structures involving large deformation must be analysed using non-linear theories. In this paper, element free Galerkin method (EFGM) has been applied to solve large deformation problems using updated Lagrangian approach. Geometrically nonlinear problems have been simulated assuming linear elastic material behaviour. The results obtained by EFGM have been compared with those obtained by FEM and analytical solutions. An elasto-plastic edge crack problem has been solved using nonlinear material behaviour and large deformation kinematics.

Abstract: Phase transitions can be usually observed in nature and technology which effectively utilize certain types of these transitions. An approach to modeling phase transition processes on the basis of the mathematical theory of growing solids is developed. Liquid-solid and gas-solid phase transitions are under consideration. Main attention is paid to the processes of solid phase growth and deformation.