A comprehensive review of functionally graded materials and their ballistic impact performance: Current status and future challenges

The designing of ballistic resistance armors, which can efficiently withstand and dissipate the enormous energy of high-velocity projectiles or bullets without sacrificing protection, is a very critical task. Armor must resist penetration and control the transmission of kinetic energy to minimize blunt force injuries during impact, all the while preserving structural integrity and avoiding becoming excessively bulky or heavy. Advanced materials are essential for resolving these problems. In the current era, functionally graded material (FGM) is replacing conventional and composite materials very rapidly due to its advanced characteristics. Lightweight FGMs can significantly improve the efficacy of armor against ballistic impact by progressively changing the material compositions and porosities over thickness without sacrificing flexibility or durability. With this gradation, FGMs may combine the energy-absorbing properties and toughness of metals, polymers, ceramics, composites, or their combinations to resist penetration against ballistic impacts. However, this paper summarized the in-depth classifications of FGMs, ammunition used for ballistic impacts, and FGMs ballistic performance. A critical correlation between the various standards of ballistics tests is developed in this article. Methods of ballistic testing with shoot spacing patterns for different standards are well described. The ballistic performance of conventional, composite, and hybrid FGMs used as plate and sandwich structures is also compared in terms of their failure modes, ballistic limit, and energy absorption capabilities. By strategically stacking different materials in the armor, the danger of catastrophic failure can be effectively reduced. This article also provides an insight into key future challenges and scopes of the FGM armors.