| Summary: | Shape memory polymers (SMPs) have been studied for using in self-healing structures through a bio-mimetic self-healing scheme recently. This scheme requires programming of the SMPs before service. One potential application of SMP based self-healing composites is in impact tolerant lightweight structures. It is desired to know whether the service load such as an impact load at service temperature (usually in glassy state) could serve as programming or not.
Strain rate effects on shape memory behavior of polystyrene-based thermoset SMP were systematically studied in this work. Several groups of polystyrene-based thermoset SMP samples were programmed at glassy state temperature under the strain rate of 1500s-1, 0.1s-1 and 0.0001s-1 respectively with a 12% pre-strain level. Free shape recovery was conducted to investigate the shape recovery behavior. The effect of programming strain rate on other physical/mechanical properties such as dynamic modulus, glass transition temperature, chemical bonds, damage and micro-crack was also investigated using Dynamic Mechanical Analysis (DMA), Differential Scanning Calorimetry Analysis (DSC), Fourier Transform Infrared Spectroscopy (FTIR), Ultrasonic Non-destructive Testing System (C-Scan) and Scanning Electron Microscope (SEM).
Results indicate that this thermosetting shape memory polymer can be programmed at glassy state temperature even at high strain rate. This study suggests that the impact load will not only cause damage to the structure, it may also serve as cold-compression programming to the SMPs and lead to healing of impact damage per the two-step bio-mimetic scheme even without the classical programming process.
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