Performance Evaluation of Sandwich Composites with Functionally Graded Core for Ballistic Impact

Abstract

Sandwich composites with flexible skin and stiff core are appropriate for a wide range of engineering applications because of their capacity to withstand greater deformation while maintaining a high load-carrying capacity. The main objective of the current research includes material selection, fabricating, and analyzing functionally graded sandwich composite for ballistic impact applications. Statistical Six Sigma DMAIC methodology was used for material selection, incorporating qualitative and quantitative approaches, ensuring a comprehensive and accurate material selection process. Considering a careful literature review, the choice of jute and rubber for skin material paired with epoxy and sea sand for core material in the sandwich composite. Finite element (FE) studies, based on the rule of mixtures, estimated composite material properties, showing increased energy absorption and a decrease in residual velocity with higher filler composition (0% to 30%) at velocities of 10, 50, 100, and 350 m/s, and with core thickness from 10mm to 30mm at 350 m/s. Following the initial FE studies, experimental testing was conducted on composite coupons to evaluate their physical and mechanical properties. The gradation test was performed to check the functional gradience for the core material. These tests provided insights into sea sand's spatial distribution and gradation within the core samples, emphasizing the impact of sea sand composition on the stepwise layering gradation. The void % (3.44%) in the composite coupons increases as the filler composition increases. Specific tensile strength decreases (2.41 times) with an increase in the filler composition. Hardness (12.47%), Flexural strength (27.93%), and impact strength (2.35 times) increase as the filler composition increases compared to neat epoxy. High strain rate compression strength is improved with higher strain rates. The FE analysis for low and ballistic impact testing was conducted based on the properties obtained experimentally from the composite coupons. For low-velocity and impact testing, it is observed that a sandwich with 30% sea sand composition has superior damage resistance capabilities compared to its counterparts. Both experimental and FE analyses show that higher filler percentages lead to increased energy absorption. The sandwich composite with 30% sea sand exhibited the lowest depth of damage and minimized overall damage across all impact energies, demonstrating superior damage resistance compared to other compositions. For ballistic impact, the similar trend that increasing the volume percentage of sea sand and core thickness improved energy absorption, with a 30 vol% sand content and 30mm core thickness performing the highest energy absorption capability compared to its counterparts. The results indicate that while thinner cores (10 mm) are inadequate for arresting projectiles, thicker cores (20 mm and 30 mm) show progressively better performance, with the 30 mm core providing the most effective ballistic impact protection. Incorporating sea sand into epoxy reduced costs by 8.9% to 32.47%, making it an economical core material for ballistic impact applications. Experimental and FE simulations for the entry area at 200 m/s showed a damage area percentage error of about 12.61%. Fractography analysis indicated face sheet damage from compression and bending, fiber breakage, rubber tearing, and core failure from sand particle crushing and matrix cracking, with a river like pattern suggesting brittle failure.