An analytical model is presented for the ballistic impact behavior of ceramic-composite armors. The model is based on wave theory and energy balance between the kinetic energy of the projectile and the energy absorbed by different mechanisms. The armor analyzed consists of front composite cover layer, ceramic plate, rubber layer and the composite backing plate. The projectile is cylindrical. The major damage and energy-absorbing mechanisms are compression of the target directly below the projectile, compression in the surrounding region around the point of impact, formation of ring cracks and radial cracks in the ceramic leading to tensile failure, shear plugging, pulverization of the ceramic, tension in the yarns, delamination and matrix cracking in the composite, bulge formation on the back face of the composite backing plate and friction between the target and the projectile. Projectile erosion and deformation are also considered. Kinetic energy, velocity and deceleration of the projectile, distance traveled by the projectile and the contact force are presented as a function of time. Ballistic limit velocity, contact duration and damage progression are also given. Further, solution procedure is presented for the study of ballistic impact behavior of ceramic-composite armors. Analytical predictions are validated with the experimental results. Finally, performance of a typical ceramic-composite armor is presented.

Experimental studies are presented on the ballistic impact behavior of nanoparticle dispersed materials viz. symmetric balanced cross-ply laminates made using unidirectional E-glass fabric with epoxy resin and neat epoxy resin. The nanoparticles used are nanosilica and multi-walled carbon nanotube for polymer matrix composites and nanosilica for epoxy resin. For comparison, studies are carried out on symmetric balanced cross-ply E-glass/epoxy and neat epoxy resin without nanoparticles. Effect of nanoparticle dispersion on ballistic limit velocity, V50 and energy absorbed has been studied. It is observed that V50 can be enhanced up to 6.3% for polymer matrix composites and up to 7.3% for neat resin on addition of nanoparticles. Also, energy absorbed can be increased up to 13.0% for polymer matrix composites and up to 15.2% for neat resin on addition of nanoparticles. Damage and energy absorbing mechanisms for different types of materials studied is also presented. Further, it is observed that the damage size on the target around the point of impact decreases on addition of nanoparticles. Quantitative data are given for high velocity impact behavior of the five types of specimens studied.

A phase-field damage model for orthotropic materials is proposed and used to simulate delamination of orthotropic laminated composites. Using the deviatoric and hydrostatic tensile components of the stress tensor for elastic orthotropic materials, a degraded elastic free energy that can accommodate damage is derived. The governing equations follow from the principle of virtual power and the resulting damage model, by its construction, conforms with the physical relevant condition of no matter interpenetration along the crack faces. The model also dispenses with the traction separation law, an extraneous hypothesis conventionally brought in to model the interlaminar zones. The model is assessed through numerical simulations on delaminations in mode I, mode II, and another such problem with multiple initial notches. The present method is able to reproduce nearly all the features of the experimental load displacement curves, allowing only for small deviations in the softening regime. Numerical results also show forth a superior performance of the proposed method over existing approaches based on a cohesive law.

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