Repeatable self-healing of thermosetting fiber reinforced polymer composites with thermoplastic healant

This paper presents the study of repeatable self-healing capability of thermoplastic healing agent poly-caprolactone (CAPA-6506) and shape memory polymer (SMP) in a fiber reinforced polymer composite structure. This self-healing is inspired by the bio-mimetic process of 'close then heal' mechanism where the thermally actuated SMP causes the closing of cracks and the thermoplastic healing agent performs the healing. In this study, two types of sixteen layered unidirectional carbon fiber reinforced thermoset polymer (SC-780) composites were tested: (1) with SMP (containing 6.4 vol% of CAPA and 0.6 vol% of SMP), and (2) without SMP (containing 6.4 vol% of CAPA only). To quantify the healing efficiency in terms of Mode-I interlaminar fracture toughness, double-cantilever beam tests were carried out for seven separate healing cycles by following the ASTM-D5528-13 standard. The tests yielded promising results as maximum healing efficiency of 73%, and 63% were achieved for with SMP and without SMP specimens, respectively. In addition, increased surface roughness due to the crack deviation, SMP pullout, SMP and CAPA bridging between the layers, and plastic deformation of the matrix that are responsible for crack growth resistance were observed during fractography analysis. Also, the relationships between the composition and material properties of epoxy and healants were thoroughly investigated via Fourier transform infrared (FTIR) spectra and differential scanning calorimetry (DSC).