Impact response and failure behavior of adhesive-bonded aluminum-wood lightweight composites

Metal-wood composites are promising lightweight materials for substituting traditional steels or aluminum alloys in automotive applications. This study investigates the pendulum impact response of 4 mm-thick solid birch plates and laminates made of 1 mm-thick birch veneers adhesive-bonded to a 1 mm-thick 6016-T4 aluminum alloy sheet. Unidirectional wood fiber orientations (longitudinal, 0°, or transverse, 90°) and bidirectional (alternating, 0°/90°) layups were considered. Maximum impact forces were determined from force-displacement curves, whereas absorbed energies were recorded by an instrumented pendulum impact tester. High-speed camera images were correlated with force-displacement curves to analyze failure behavior. Regression analyses showed that wood fiber orientation had the strongest influence on the impact response, while the impact side significantly affected absorbed energy but not maximum force. Impact loading parallel to the wood fiber (0°) increased maximum force by 353-474% and absorbed energy by 92-223% compared with loading perpendicular to the wood fiber (90°). When impacted on the wood side, the aluminum alloy sheet effectively mitigated wood splintering, resulting in higher absorbed impact energy. In contrast, impact on the aluminum alloy side caused brittle tensile failure of wood and substantially decreased the absorbed impact energy. Aluminum-wood composites impacted on the wood side exhibited 139% higher maximum force and 247% higher absorbed energy than pure aluminum alloy sheets of equivalent weight, with only slight debonding between the aluminum alloy and wood. These results demonstrate the high lightweight potential of aluminum-wood composites and highlight the strong dependency of impact performance from the failure mechanisms of the composites.