Analysis of the synergistic regulation mechanism of “stiffness – toughness” and spatial failure mechanisms in epoxy-based composites under low-speed impact

Polymer matrix composites exhibit exceptional performance advantages and a wide range of potential applications. However, these materials are highly susceptible to low-velocity impacts during service, which can induce internal damage such as delamination and matrix cracking, significantly compromising structural integrity and long-term functional reliability. This study investigates the enhancement of low-velocity impact in glass fiber-reinforced polymer (GFRP) composites through modified epoxy resins, focusing on the synergistic effects of resin modulus and toughness on damage behavior, as well as the spatial evolution of failure modes in laminates under impact. A combined methodology of experimental testing, numerical simulation, and parametric analysis was employed. Three distinct epoxy systems were used to fabricate glass fiber laminates, which were subjected to drop-weight impact tests at energy levels of 60 J and 90 J to obtain dynamic response curves and damage morphology. Principal Component Analysis (PCA) was applied to quantify the influence of static mechanical properties on impact behavior and identify key material indicators. A mesoscale finite element model incorporating cohesive elements was developed to elucidate damage propagation mechanisms and failure modes under impact loading. Results indicate that damage evolution through the laminate thickness exhibits distinct zonal characteristics: a compression-dominated impact face, an energy-absorbing intermediate layer, and a tension-dominated failure zone on the back surface. Furthermore, a significant nonlinear relationship exists among resin modulus, toughness, and impact energy. These findings provide theoretical insights and design guidance for developing lightweight impact-resistant composite structures.