Adhesive bonding in impact crushing of automotive Al-CFRP hybrid tubes: a theoretical, experimental and numerical investigation

This study investigates the crashworthiness of Aluminum-Carbon Fiber Reinforced Polymer (Al-CFRP) hybrid tubes, which are bonded with adhesive and subjected to quasi-static and impact loading. The research introduces a novel approach to enhance energy absorption in automotive structures. To predict the average crushing force of these hybrid designs, theoretical models were developed and validated, combining the high strength and specific stiffness of composites with the structural rigidity of metals. Validation through experimental testing and finite element analysis showed strong alignment with theoretical predictions. The results suggest that increasing the fiber orientation angle, the thickness of the layers, and the quantity of CFRP layers generally boosts the energy absorption capacity. A finite element model was developed to evaluate these hybrid structures, focusing on five different composite ply angles: [+15/-15], [+45/-45], [90/90], [0/90], and [90/0]. The number of composite layers ranged from 2 to 8, with both uniform and variable thicknesses considered. Furthermore, an alpha factor was applied to evaluate local reinforcement effects. Findings showed that in comparison to energy absorbers made from aluminum or aluminum/composite materials, the adhesive bonding in the locally reinforced (Al-CFRP) specimen enabled the composite to enhance its energy absorption by conforming to the aluminum's collapse behavior, resulting in a consistent collapse mode. It was also found that the loading rate has minimal influence on the deformation pattern in both hybrid and single-material tubes. However, the energy absorption capacity of hybrid and CFRP tubes was considerably lower under dynamic loading compared to quasi-static loading. The effects of impact velocity and stacking sequence on the Dynamic Amplification Factor (DAF) were analyzed, This factor is important in simple design procedure as it can be used to estimate the dynamic effect from the static analyses without con ducting actual dynamic analyses or tests. Interestingly, the DAF for hybrid structures was lower than that of aluminum tubes, suggesting that lateral inertia effects in hybrid structures are diminished relative to empty tubes.