Experimental assessment of effects of elevated temperature and hygrothermal aging on the axial impact response of CFRP laminated tubes

This study investigates the effects of elevated temperature and hygrothermal aging on the dynamic axial crushing response of carbon fiber-reinforced polymer (CFRP) tubes. Cross-ply and angle-ply tubes, manufactured from the same unidirectional CFRP/epoxy material, were evaluated to assess the influence of laminate stacking sequence on crashworthiness under environmental degradation. Two conditioning protocols were employed: (i) thermal exposure at 50°C and 75°C, and (ii) hygrothermal aging through water immersion at 25°C and 75°C for 50 days. Dynamic axial crushing tests were conducted using a drop-weight impact system at an impact velocity of approximately 6 m/s. To examine the reversibility of moisture-induced degradation, a subset of the specimens aged in water at 75°C was subsequently re-dried at 40°C for three days. The crushing performance of conditioned and unconditioned tubes was evaluated in terms of macroscopic failure modes, specific energy absorption (SEA), and mean crushing force. Both thermal and hygrothermal conditioning reduced crashworthiness, with elevated temperature producing the most pronounced degradation. Although the overall crushing mechanisms remained unchanged, conditioned specimens exhibited evidence of increased ductility. The limited recovery observed after re-drying indicates that hygrothermal aging induces irreversible mechanical degradation. Moisture uptake was strongly influenced by the laminate architecture, with angle-ply tubes absorbing approximately 45% more moisture than cross-ply tubes after aging at 75°C. Furthermore, stacking sequence significantly affected impact performance, as cross-ply tubes consistently exhibited higher crushing stability and energy absorption under elevated-temperature conditions. This superior performance is attributed to their fiber-dominated crushing mechanism, which is less sensitive to matrix degradation than the matrix-dependent response of angle-ply laminates. These findings demonstrate that environmental exposure and laminate architecture should be considered jointly when designing CFRP energy-absorbing structures, as crashworthiness assessed under unconditioned conditions may not adequately represent in-service performance. The results provide practical guidance for the selection of laminate configurations for crashworthy composite components operating in thermally and hygrothermally demanding environments, with relevance to transportation and aerospace structures.