Effect of the electric current on the stress relaxation behaviour of CFRP composites

Abstract There are no studies about stress relaxation of composite laminates after long exposure to low value electric currents. This phenomenon is very important because significant effects are expected in those materials when used in long-term applications. Therefore, the present study aims to analyse and quantify the effect of exposure to DC electric currents flowing through-thickness of the sample on the stress relaxation behaviour of carbon/epoxy laminates. For this purpose, flexural and stress relaxation tests were performed on the bending mode. It was possible to conclude that the residual flexural strength is significantly affected by the exposure time and magnitude of the electric currents. Comparatively to control samples, for example, 4 h of exposure to an electric current of 3 A promote a decrease in bending stress around 5 times higher than that observed for 1 A. From the stress relaxation tests, a decreasing of the stress over the time was observed and this tendency increases with the exposure time and the electric current magnitude. In this case, the decrease observed after 4 h of exposure is 28.6% and 30.8% higher than those observed for 1 h of exposure for currents of 1 A and 3, respectively. The Kohlrausch-Williams-Watts (KWW) model fits the experimental data with good accuracy, and it shows to be a good methodology to predict the stress relaxation against the time.