Effect of Uniaxial Compression on the Shape Memory Behavior of Unidirectional Vitrimer Composite Embedded with Shape Memory Polymer Fibers

A major challenge polymer composites face is micro-cracking that results from various loading conditions. The affected structural members release energy in the form of micro-cracks, which could worsen with time and impair the functionality of the member. In recent studies, these propagating cracks are braced and closed by taking advantage of the shape-recovery property of shape memory fibers or shape memory matrix, before healing. For self-healing composites embedded with tensionprogrammed shape memory polymer fibers as sutures, the composites may be subjected to compression loading during service. Compression loading may reduce the stored strain in the embedded pre-stretched fibers, and thus reduce the shape recovery strain and limit the ability to close cracks. If the matrix is also a shape memory polymer, a compression load to the composite includes the matrix as well. Consequently the matrix would expand when the composite is heated thereby mitigating the shrinking ability of the pre-stretched fibers. The purpose of this study is to investigate the shape memory effect of the composite when pre-stretched shape memory fibers are embedded in a shape memory polymer matrix, in particular, the shape memory effect of the composite if the composite is subjected to compressive load during service. To this purpose, pre-stretched shape memory Polyethylene Terephthalate (PET) fibers with different fiber volume fractions were embedded into a shape memory vitrimer. The shape memory effect of both the PET fiber and the vitrimer was investigated. The effect of compression load on the shape memory behavior of the composite was studied. It is found that, uniaxial compression on the composite along the fiber direction significantly reduced the shrinking ability of the embedded pre-tensioned shape memory polymer fibers, and thus it is a factor that needs to be taken into account when designing such type of self-healing composites.