Thermal cycling and ultraviolet radiation effects on fatigue performance of triaxial CFRP laminates for bridge applications

Environmental processing such as thermal cycling and ultraviolet (UV) exposure contributes to degradation of polymer composites mechanical properties. This study focuses on assessing fatigue life of both unstressed and stressed triaxial carbon/epoxy composite laminates exposed to both thermal cycling and UV radiation. In this study, five test series were conducted to assess such effects on fatigue life of carbon fiber reinforced polymer laminates exposed to tensile-compressive (T-C) fatigue loading. This included the following: (i) Pre-exposure (baseline) test group tests; (ii) unstressed thermal cyclic aging; (iii) stressed (tensioned) thermal cyclic test group; (iv) stressed (compressed) thermal cyclic test group; and (v) UV radiation exposure test group. Fatigue life with 95%, 97.7%, and 99% guarantee rates is calculated based on stochastic analysis. In terms of different guarantee rates, the material parameters of S-N curves are fitted after transforming the data to a log-log space. Experimental results indicated that the difference of parameter sigma(0) is relatively small for different guarantee rates, and that the coefficient m decreased with increasing probabilistic guarantee rate. Furthermore, the ratio N-x/N-50 decreases with larger guarantee rates and increases as the stress range increases. Results of this study indicated that UV radiation exposure has the largest effect on fatigue life stress range less than 500.0 MPa. Also, fatigue life of pre-compressed specimens exposed to thermal cyclic is most affected when exposed to stress levels larger than 500.0 MPa. For stress ranges less than 500.0 MPa, the effects on fatigue life of unstressed and pre-compressed thermal cycled specimens are relatively large as compared to baseline group.