Polarization Raman spectroscopy characterizations of microscopic stress in 3D angle-interlock woven composites during thermo-oxidative ageing

Abstract

Investigating stress distribution of three-dimensional carbon fiber epoxy woven composites after thermo-oxidative ageing, especially the microscopic stress, is key to safety design of composite materials. Here, polarization Raman spectroscopy combined with the Raman stress sensitivity of carbon fiber was employed to characterize the microscopic stress in the carbon fiber along the warp and weft direction, as well as the microscopic stress mapping in the warp and weft interwoven interfaces. Under thermo-oxidative ageing, the carbon fiber was forced with compressive stress caused by the thermo-oxidative shrinkage of resin. The fitting lines of compressive thermo-oxidative ageing stress (TAS) distribution in the warp and weft were similar to the yarn alignment paths. Meta-regression analysis indicated that the compressive TAS in carbon fibers is positively correlated with ageing time. Furthermore, the correlation between the compressive TAS and ageing time in warp yarns is greater than that in weft yarns. The stress distributed unevenly with the synergistic effect of the structure and ageing time, and interfacial failure was generated where interfacial stresses exceeded the interfacial strength. The interfacial failure further propagated with ageing time, leading to matrix cracking.