Effect of hostile solutions on stress relaxation of carbon/epoxy composites

Polymeric composites are prone to stress relaxation as consequence of the matrix phase viscoelasticity. On the other hand, when this phenomenon is associated to the effect of hostile environments, it reveals to be a great challenge for long-term applications. Therefore, this work intends to study the effect of hostile solutions on the stress relaxation behaviour of carbon fibre reinforced polymers (CFRPs). For this purpose,. hydrochloric acid (HCl) and sodium hydroxide (NaOH) were the selected solutions, and the effects of exposure time (15, 30 and 60 days), temperature (room temperature and 40 degrees C) and solution's concentration (10 and 20% wt.%) are analysed. It was possible to conclude that, independently of the corrosive solution, a decreasing of the stress against time is observed, but strongly dependent of the exposure time, temperature and solution's concentration. For example, the stress decreases about 0.8% from its initial value for the control samples, while 60 days of immersion into HCl and NaOH solutions promote a decrease around 1.7% and 2%, respectively. These values are 33.3% and 16.7% higher when the temperature increases to 40 degrees C and 6.7% and 18.8% when the solutions' concentration increases from 10% to 20%, respectively. Finally, to predict the effect of hostile solutions on stress relaxation, the Kohlrausch-Williams-Watts (KWW) equation was used to fit the experimental results, and good accuracy is observed. (C) 2019 Elsevier Ltd. All rights reserved.