Bending shape recovery of unidirectional carbon fiber reinforced epoxy-based shape memory polymer composites

The thermo-mechanical properties of unidirectional carbon fiber reinforced epoxy-based shape memory polymer (SMP) composites with fiber mass fractions of 16%, 23%, 30%, 37% are evaluated by using three-point bending tests. The SMP composites show temperature-dependent flexural modulus and strength, with one order of magnitude difference between 120 degrees C and 20 degrees C. The composites show good shape recovery capability, with measured recovery ratios of more than 93% at 120 degrees C and 100% after 20 min at that temperature. The recovery stresses increase nonlinearly during reheating; the maximum recovery stress is approximately proportional to the fiber mass fraction. The composites show recovery capability under external loads, with the recovery ratio being inversely proportional to the partial load level. The composites feature good shape memory properties during cyclic loading and unloading at 120 degrees C. Their loss factors and stiffness losses decrease significantly during the first three cycles, and then stabilize after ten cycles.