Effect of high temperature on mechanical properties and porosity of carbon fiber/epoxy composites

In this study, the mechanical behavior and porosity of a T700/epoxy composite material under high temperature conditions were investigated. The 0°/90° compression, tensile, interlaminar, and in-plane shear experiments of composite samples were performed at temperatures from 23°C to 170°C. The true strain–stress curves of composite samples were obtained. The cross section and fracture regions of the tested samples were analyzed by Scanning Electron Microscopy and X-ray tomography to understand the microstructure property relationships. It was observed that the mechanical performance of carbon fiber/epoxy composites generally decreased with increasing temperature. By comparing the fracture morphology, it was found that the fracture mechanism of the composites changed from interfacial debonding to matrix failure with increasing temperature. Three-dimensional visualization of porosities after mechanical experiments under high temperature conditions was reconstituted from X-ray tomography scan images. The results showed that the porosity fraction of the tested samples under high temperature conditions was generally higher than that under lower temperature conditions. Moreover, for the 90° tensile test, the diameter of the pores was mainly located at 4–12 μm and was almost constant along different distances to the failure edge. Meanwhile, compared with the tensile test, larger size of pores in samples of 90° compression tests were observed.