Effect of composite fiber and layer thickness on ballistic impact of soft projectile against Kevlar based armoured target

• Interaction of 5.45 mm bullet on Kevlar with water infill targets is investigated • Soft projectile and Armour material behaviour are observed under impact • Targets, classified by Kevlar and water thickness sequencing of total 15 numbers • Evaluation of Velocity, Internal and Kinetic energy, and Total mass • Inference of these findings supports understanding of layer thickness effects • Factorial analysis enhances accuracy in predicting ballistic responses . Ballistic impact is a critical domain of terminal ballistics, where a projectile interacts with protective systems such as soft body armor. This study investigates the ballistic response of kevlar fiber reinforced plastic (KFRP) layered with water infills under impact from a 5.45×18 malokalibernyj pistolentyj tsentralnogo boya (MPTs) centerfire bullet, modeled as a soft lead projectile. Finite element method (FEM) simulations were conducted using ANSYS/Autodyn at 350 m/s on targets consisting of 13 KFRP layers and 12 water infills with clamped boundary conditions. Results indicate that KFRP layer thickness predominantly governs velocity attenuation and energy dissipation. The highest velocity drop of 12.494 m/s was achieved for 0.5 mm KFRP layer with 0.1 mm water infill, where kinetic energy absorption reached 10.674×10⁵ μJ in water and 3.372×10⁶ μJ in KFRP layer. By using idealized water infills to overcome stacking and resin inconsistencies, this study systematically evaluates thickness effects on ballistic resistance. The approach reveals how KFRP layer and water infill configurations influence velocity drop, kinetic energy absorption, and internal energy transfer. Factorial regression and ANOVA confirmed that KFRP layer thickness has a statistically significant effect with major influence, whereas water infill thickness has the secondary contribution with marginal influence. It introduces a coupled FEM and statistical modeling framework to quantify the interaction between structural parameters and ballistic behavior. The findings provide novel insights into soft projectile against composite layered with fluid infilled armor interactions and offer a predictive basis for optimizing lightweight personal protective systems.