Study On The Anti-Penetration And Failure Mechanism Of 3-Dimensional Woven Composites

As fiber-reinforced composite is used extensively in defense engineering, study of the mechanical response, ballistic performance and failure mechanism of composite under impact loading being the hot-topic by the researchers in and out. Three-dimensional woven composite can overcome the defects of traditional laminates which are apt to delaminate and have low interstratified strength, because there are reinforced fibers along the thickness direction, which can improve the composite's mechanical property, but the research works are still quite limited in this area, for example the multi-phase structure, anisotropic multi-strain.rate and damage modes, and the penetraion mechanism on it and so on. In this paper, systemic studies including experiments, engineering analyses methods and numerical simulations on the dynamic-static mechanical property and penetration property and failure mechanism of 3D Kevalr/vinyl orthogonal Woven composites(3DKW).On the theory of constitutive relation and constitutive algorithm, a strictly theoritical testification of the radial-returan method on Misess material is given, based on the radial-return method ,a general return algorithm is deduced and its applicability is also discussed. On the modified Drucker's postulate, the universal form of the thermo-visco-plastic incremental constitutive relations which is including multi strain rate and multi-damage mode, just is the self-consistent incremental algorithm of visco-plastic flow, then the universal single strain rate parameter constitutive relation is dedued; it can easily and fitly describe the anistropic strainrate material; More,the position of hydrostatic pressure in the constitutive relation is studied, and the determination of parameters on Equation Of States are also studied.The dynamic-static mechanical properties of 3DKW composites are studied by a series of MTS quasi-static experiments and SHPB dynamic experiments, the main parameters of basic mechanical are obtained, furthermore, the Hill-Tsai model is got, which is used to describe the mechanical of 3DKW composites. Based on the experiment results, the strain-rate of strength and the damage patterns under different load are analyzed.On the ballistic experiment of 3DKW, a series of penetration experiments are carried out by spherical and cylindrical projectiles within velocity from 500m/s to 1100m/s. Based on the experiment results, the effects of projectile shapes, target thickness and the coarse of fiber on penetration resistances are investigated, the failure modes and absorbed energy mechanism of target are analyzed within different initial velocity. Based on the high velocity penetration experimental results, the definition of "critical consumption energy" is proposed, which is assumed to be a function of the initial kinetic energy of bullet, and so a new engineering method to forecast the ballistic limit (V₅₀) is presented, compared with the traditional surface-density method and the residual energy method which is used to forecast the ballisti limit value are more simlar to the experimental V₅₀ value which is directly got by the direct measurement method.On the engineering analysis method of penetration, An engineering analysis method of computing the penetration of a metal ball into fibre-reinforced composite targets is presented, the modified model which the spherical cavity dilatation model is coupled with the cylindrical cavity penetration method is presented. In the simulation, the sphere is regarded as rigid body and the 3DKW composite target is assumed to a transversely isotropic elasto-plastic material, the strength of 3DKW targets' strain-rate, the modification of anistropic behavior, the floating lock strain being calculated by a zone-average method and the kinematic modification are also considered. The simulation results are in good agreement with the results for the 3-D Kevlar Woven composite (3DKW) anti-penetration experiments.On the finite element method, A series of new numerical method are investigated, such as the new algorithm of the sliding interface in the penetration computations, and a new damage switch to control the element failure and so on, by introduce the self-consistent incremental algorithm of visco-plastic flow and the generalized radial-return method for anisotropic elasto-plastic material constitutive calculations, the original high velocity penetration (HVP)software is improved greatly;A series numerical simulations of 3DKW composite plate penetrated by a steel ball are carried out by the improved HVP. The numerical results of the penetration process, the history of bullet velocity and the residual velocity of the ball are fitted with the experimental results well, which indicates strongly that the numerical simulations and the new software we developed are rational and effective in the study of ballistics resistance of fiber-reinforced laminates. Finally, the physical mechanism of failure and anti-penetration of 3-DKW composites are also studied .