Impact resistance and damage mechanisms of CFRP/foam/aluminum sandwich structures under impact loading by fragments

To enhance the impact resistance of composite sandwich structures subjected to high-velocity fragment impacts, a thin aluminum alloy plate was embedded into a conventional carbon fiber reinforced polymer (CFRP)/foam sandwich. Seven CFRP/foam/aluminum (CFA) configurations with varying aluminum alloy positions were designed and fabricated. High-velocity impact tests were conducted to investigate the dynamic response, energy absorption characteristics, and failure mechanisms of these structures. The results showed that the position of the aluminum alloy plate significantly influenced the impact resistance. Configurations with the aluminum alloy plate positioned near the front CFRP facesheet demonstrated superior performance, as the plate effectively dissipated energy through plastic deformation without contacting the rear facesheet throughout the impact event, thereby avoiding compression stress concentrations and aggravated damage. This configuration led to improved energy absorption and overall impact resistance. As the aluminum alloy plate was moved closer to the rear facesheet, the foam failure mode transitioned from compaction to fragmentation and plug formation, reducing the structure’s energy absorption efficiency. However, when the aluminum alloy plate was located within the rear half of the core, its exact position had a less pronounced effect. Across all configurations, the front facesheet consistently exhibited brittle fracture, while failure of the rear facesheet evolved from fiber breakage to a mixed mode involving fiber fracture and interlaminar delamination as the aluminum plate shifted rearward. Significant interfacial debonding between the aluminum alloy plate and adjacent layers was also observed. Numerical simulations corresponding to the experiments were performed using PAM-CRASH software, and the calculated results showed good agreement with the experimental data, confirming the rationality and accuracy of the numerical model. By combining the fitted correlation equation between the aluminum alloy plate embedding position and the structural energy absorption, the study further revealed the damage evolution of the CFA sandwich structure during the impact process.