Ballistic performance of functionally graded B4C/Al composites without abrupt interfaces: experiments and simulations

Abstract

Functionally graded materials (FGMs) are promising protective structures for lightweight armor plates because of their features and designability. However, traditional discretely layered FGMs with macroscopic interfaces can generate unfavorable interlaminar stresses under ballistic attacks, eventually leading to delamination or interlayer tearing. Herein, we constructed new B4C/2024Al FGMs without sharp interfaces between layers. The FGM armor systems with varying through-the-thickness distributions were tested against 7.62 mm armor-piercing incendiary projectiles. The effects of compositional gradient exponent on the damage characteristics, stress distribution and energy evolution were numerically and experimentally investigated. The results indicated that the smooth transition within through-the-thickness microstructures effectively avoided the occurrence of interlayer delamination or tearing. The compositional gradient exponent played an essential role in the impact response of the FGM targets. The FGM having a linear composition gradient outperformed other nonlinear types with respect to energy absorption and ballistic properties due to the reduced tensile wave strength and prolonged projectile-target interaction time. Furthermore, the structural optimization problem with the objective of maximizing ballistic efficiency was solved using the conjugate gradient method, and the optimal design of the FGM targets was achieved. The current research provides a promising design guideline for developing and optimizing new advanced lightweight composite armor.