In-situ Healing of Mode-I Fatigue Crack in CFRP Composite Using Thermoplastic Healant

Abstract

The healing performance of Mode-I interlaminar fracture of a carbon fiber-reinforced polymer (CFRP) composites subjected to fatigue loading is investigated in this research. Laminated composites are highly susceptible to delamination, and delamination due to fatigue loading is one of the most critical damage modes in composite structures that may lead to a catastrophic failure. Hence, it is paramount to investigate and quantify the delamination crack growth behavior due to fatigue loading and explore methods to heal the delamination. To this end, double cantilever beam (DCB) specimens of a carbon fiber-reinforced polymer (CFRP) composite containing thermoplastic healants were manufactured, and the Mode-I fatigue delamination experiments were carried out for virgin and five healing cycles. In this study, in-situ healing performance of Mode-I interlaminar fracture of CFRP composites subjected to fatigue loading up to seven healing cycles was investigated. The main purpose of using thermoplastic healants (polycaprolactone (PCL) and shape memory polymer (SMP)) was to heal the cracks formed during fatigue loading as well as to regain its load-carrying capacity. To establish proof of concept, the healing was initially achieved with the help of a convection oven where the heating is provided to close the cracks using thermoplastic healants. From experimental data for virgin and healed specimens, the Paris law parameters were extracted, and the results obtained from different specimens were found to be repeatable upon the comparison. Furthermore, the slope parameter of the Paris law for the healed specimens was found to be almost 75% ~ 86% of the virgin specimen, thereby indicating slower crack growth in the healed specimens under fatigue loading. Subsequently, in-situ delamination healing was performed by activating macro fiber composite (MFC) actuators attached to the DCB specimen after 5000 cycles of loading. For the fifth, sixth, and seventh healing cycle, the crack closure observed after insitu healing was significant with 10% ~ 12% reduction in crack growth after 21000 cycles with respect to the virgin cycle. These findings are envisioned to be very helpful in extending the service life of self-healing composite smart-structures and thereby provide huge repair cost savings.