Effect of thermal cycle on mechanical properties of aluminium laminated composites reinforced with different synthetic fibers

In this study, the effect of thermal cycling process on the mechanical properties of aluminum layered composite materials reinforced with different fibers was investigated experimentally. Within the scope of the research, ten different layered composite structures (Arall, Carall, Glare, Barall, Ar-Carall, Ar-Glare, Ar-Barall, Car-Glare, Car-Barall and Gl-Barall) consisting of a total of five layers were fabricated using 2024-T3 aluminum alloy sheet and glass, carbon, basalt and aramid fibers individually or in combination by vacuum bagging method. The 1st, 3rd and 5th layers of the composites were made of aluminum sheets, while the 2nd and 4th layers were made of determined fiber reinforcement combinations. Some of the fabricated composite samples were separated for direct mechanical testing; the other part was subjected to different numbers of thermal cycling processes. Thermal cycling was applied between –45 °C and +75 °C with a temperature difference of 120 °C and these cycles were carried out in the 5th, 15th, 25th, 50th, 100th and 150th cycle numbers, respectively. After the cycling, the mechanical behaviors of the composite samples were evaluated by tensile test, flexural test, notch impact test, short beam shear (SBS) test and quasi-static penetration test (QSPT). In this direction, the effects of both the layered composite structure composition and the applied number of thermal cycles on the mechanical performance were analyzed comparatively and systematically. The findings revealed that thermal cycling has complex and structure-specific effects on the mechanical performance of fiber metal laminate (FML) composites. In general, it was found that while a slight increase in strength was observed in some composite types at the first cycles, this increase was partially lost with increasing cycle numbers and a recovery tendency emerged at the end of long cycles. Thermal cycling was generally found to have positive effects on the amount of elongation and energy absorption capacity. In particular, it was determined that some hybrid FML composites exhibited more stable or improved mechanical properties against thermal cycling compared to composites containing single fibers. These results show that considering thermal cycling effects in the design and application processes of FMLs is of critical importance. In addition, understanding the damage mechanisms such as internal stresses, microcrack formation and delamination resulting from the mismatch of thermal expansion coefficients between different materials will guide the development of more durable and long-lasting composite structures.