Influences of thermal cycling and low-energy impact on the fatigue behavior of carbon/PEEK laminates

Effects of low-energy impact and cyclic thermal loading on fatigue behavior of carbon fiber reinforced polyetheretherketone (carbon/PEEK) laminates ha ve been examined. The fatigue behavior of the virginal composites, low-ener gy impacted composites, and low-energy-impacted and thermally exposed compo sites were investigated. Cyclic thermal loading was performed in the temper ature range between 60 and -60 degrees C. Residual tensile strength was mea sured to aid in understanding the influence of low-energy impact on the ret ention of tensile strength. Fatigue testing involved a stress ratio of 0.1, with a frequency of 3 Hz. The Weibull distribution function was used to ev aluate the ultimate tensile strength and fatigue life. S-N curves were plot ted and the influence of thermal cycling and the low-energy impact on the f atigue sensitivity of the carbon/PEEK laminates was investigated. Stiffness variation during fatigue testing was monitored and differences in stiffnes s reduction for three rest conditions were compared. C-scan was used to inv estigate the damage zone under different low-energy impacts and to understa nd damage propagation during fatigue testing. Moreover, scanning electron m icroscopy (SEM) was used to examine the fracture morphologies of carbon/PEE K composites in both tensile failure and fatigue failure conditions. (C) 19 99 Elsevier Science Ltd. All rights reserved.