Rapid thermal degradation of polyamide 6 microdroplets and its effect on interfacial shear strength to simulate thermal welding conditions of CFRTP

Abstract

The objective of this study is to investigate the effect of rapid thermal processes on the interfacial strength of carbon fiber-reinforced polyamide 6 (PA6) and to elucidate the influence of such processes. To this end, high-speed thermal degradation tests were performed on microdroplet specimens. Initially, the thermal stability of PA6 in a simulated air environment was examined using isothermal gravimetric analysis to determine suitable thermal degradation test conditions. Then, the oxidation of the microdroplets after thermal degradation was assessed by measuring the total color difference between untreated and thermally treated specimens. Additionally, the effects of temperature and the test duration on the interfacial shear strength (IFSS) of the microdroplet specimens were investigated. Even short-term degradation tests decreased the IFSS of relatively small microdroplets, and the size of the microdroplets significantly influenced the IFSS of the resin–fiber interface. Additionally, thermal degradation at the contact area between the microdroplet and the knife edge influenced the test results. At 300 °C, the decrease in the IFSS resulting from thermal degradation was relatively small. However, at 325 °C, a longer duration of thermal exposure significantly decreased the IFSS. For specimens with an embedment length of at least 60 μm, differences in the IFSS were small when the total color difference was small, regardless of the test temperature.