Evaluation of the bending strength of preloaded CF/PEKK at high temperature

Abstract

Carbon fiber-reinforced polymer composites employed in practical aerospace applications are subjected to harsh temperature changes and preloads (PLs) simultaneously. Thus, it is important to analyze the mechanical behavior of carbon fiber/polyether-ketone-ketone (CF/PEKK) composites under such conditions. Therefore, this study first performed bending tests on CF/PEEK samples at room temperature (RT), 80[Formula: see text]C, and 120[Formula: see text]C. Subsequently, bending tests were performed on CF/PEEK samples preloaded with 30%, 50%, and 70% of the ultimate load for 24 h and 72 h. Finally, bending tests were conducted on CF/PEKK samples subjected to both temperature and PL variations. The results show that as temperature increased from RT to 120[Formula: see text]C, the strain values increased, but the modulus ([Formula: see text]) and strength ([Formula: see text]) decreased. As PL increased, the flexural stress, [Formula: see text], and strain ([Formula: see text]) decreased. The samples preloaded with 30% of the ultimate load at 80[Formula: see text]C had the highest [Formula: see text], [Formula: see text], and [Formula: see text] values. However, the [Formula: see text], [Formula: see text], and [Formula: see text] values at 120[Formula: see text]C were only slightly lower than those at 80[Formula: see text]C. This proves that preloaded CF/PEKK composites maintain their high strength, toughness, and plastic behavior at high temperatures, and thus, they are suitable for aerospace applications.