The Effect of Tension-tension Fatigue and Lay-up Configuration on Damage Accumulation in Carbon/epoxy Composites

The effect of tension-tension fatigue (T-T) on carbon/epoxy composites (CFC) has been investigated in this paper. Load controlled fatigue tests were conducted in the tension-tension (T-T) cyclic mode with the R-ratio values of 0.1 and 0.3 and subsequently the specimens with the fatigue life over 10 cycles have been studied by means of tensile testing, ultrasonic inspection and quantitative data of the internal damage accumulation. Different damage mechanisms under cyclic loading are expected for the chosen lay-up configurations and are reported herein. INTRODUCTION Different fatigue models have been established for the life time prediction of CFC. First fatigue life model extract information from the S-N curves or Goodman-type diagrams and propose a fatigue failure criterion [1]. Phenomenological models were established to predict residual stiffness and strength; meaning that the failure occurs when the applied stress equals the residual strength. In order to predict damage growth of CFC, the progressive damage models have to be used, that are based on actual damage mechanisms [2]. Additionally nondestructive techniques for monitoring the integrity of CFC, ultrasonic testing of fully cured composites and acoustic emission (AE) have been reported [3, 4]. The present work reflects a number of further references and the occurrence of the different mechanisms will be shown.