Effect of Foam Filling and Holes on In‐Plane Compressive Failure Behavior of <scp>FML</scp> Face Sheet Grid Sandwich Structures

ABSTRACT To investigate the effects of foam filling and central hole on the in‐plane compressive failure behavior of fiber‐metal laminate face sheet grid sandwich structures, this study employs a combined experimental and numerical simulation approach to systematically analyze the mechanical response and damage mechanisms of three structural types, including pure foam, unfilled foam, and filled foam, considering both their no hole and open hole states. Real‐time non‐destructive monitoring of the entire in‐plane compression process was conducted using digital image correlation and acoustic emission techniques. A three‐dimensional finite element model incorporating progressive damage to carbon fiber reinforced polymer layers, cohesive layers, and polymethacrylimide foam was established on the ABAQUS/Explicit platform using the User Material Subroutine. The model demonstrated good agreement with experimental results upon validation. The results indicate that the combination of foam and fiber grid has a reinforcing effect, thereby enhancing load‐bearing capacity and stability. Central holes induce stress concentration, leading to premature damage and reduced performance. Acoustic emission analysis using K‐means++ identified four damage modes: matrix damage, interfacial debonding, delamination, and fiber fracture. Combined with numerical simulations, this reveals the failure mechanisms for each core structure, providing theoretical and data support for designing high‐performance composite sandwich structures.