Sandwich beam with flexible core and FML face sheets under drop-weight impact and three-point bending tests

The investigation of the impact resistance of sandwich structures plays a crucial role in their safe design and reliable performance under dynamic loading conditions. Combining metal and composite layers enhances strength and impact resistance of the structure. The incorporation of nanosilica (NS) into the composite matrix enhances both the impact and flexural resistance of sandwich structures. The novelty of this study lies in the use of NS reinforced FML face sheets and the evaluation of the mechanical behavior of sandwich beams through three-point bending (3PB) and low velocity impact (LVI) tests under various energy levels. The beam surfaces consist of aluminum (Al) layers and a composite made with an epoxy (Epx) matrix that is reinforced with glass fibers (FG) and NS particles. The samples vary in the percentage of nanoparticles utilized. Initially, the efficacy of adding NS on the mechanical characteristics of pure Epx and Epx/FG composites is examined. By performing simple extension tests, the Young’s modulus (YM), tensile strength (TS), yield stress (YS), and elongation at break (EB) are assessed. Subsequently, beam sandwiches are fabricated with fiber metal laminate (FML) surfaces and flexible cores, and LVI as well as quasi-static tests were carried out on them. The samples are subjected to drop-weight impact (DWI) at seven different energy levels: 2.5, 5, 7.5, 10, 15, 20, and 25 J. The impact characteristics of the sandwich beam with varying percentages of NS are analyzed based on contact force (CF), energy absorption (E ab ), and indentation depth. These sandwich beams undergo 3PB test, and their behavior are evaluated. By analyzing the force-displacement graphs produced from this experiment, the specific energy absorption (SE ab ) and collapse force efficiency parameters are investigated. The experimental results revealed that adding 1%wt. NS to the FML structure led to a substantial improvement in energy absorption, reaching up to 36% enhancement relative to the control specimen.