Mechanical Characterization of Healable Cross-Ply Composites

Polymers with thermally-reversible Diels-Alder cross-links have been previously shown to heal cracks and regain structural integrity. Complete recovery of fracture toughness has been experimentally observed in neat samples under ideal conditions. In the present work, new healable polymer samples containing glass or carbon reinforcing fibers in [90,0]_s cross-ply orientations are fabricated and characterized using dynamic mechanical analysis (DMA). The DMA results are compared with one-dimensional composite and beam analyses. Transverse cracks observed in microscopy images and attributed to residual thermal stresses are considered using a shear lag method. Crack healing is assumed to be occurring as a function of the sample temperature, where the limits of healing are established by other experiments. By considering the composite constituent properties, sample geometries, and the presence of cracks that heal during the test, the DMA measurements are accurately modeled.