Effect of heat treatment on mechanical properties of carbon-fiber-reinforced themoplastic

Abstract

In this study, the bending properties and damage accumulation behavior of carbon-fiber-reinforced thermoplastics (CFRTP) were investigated to understand the effect of heat treatment on crystallization. Further, three-point bending tests using the acoustic emission technique were performed. Results indicated that a short period of heat treatment increased the CFRTP bending strength; however, for an excessively long heat treatment (30 h), the CFRTP bending strength decreased. To understand cause for the increase and decrement in the bending strength via heat treatment, surface observations using a laser microscope and thermal property measurement using differential scanning calorimetry were performed. Results showed that the 30-h heat-treated specimens exhibited fiber-matrix debonding before bending tests because of matrix shrinkage caused by crystallization and thermal degradation. Fourier transform infrared spectroscopy analysis revealed that the cause of deterioration was oxidation, and oxidation cleaved the molecular chains and embrittled the matrix. Consequently, we could control the bending properties by crystallization, and the relationship between crystallization and strength agreed with the formulated constitutive equation. However, we must address the thermal degradation when the materials are subjected to heat treatment.