Effects of thickness on the fatigue-behavior of quasi-isotropic carbon/epoxy composites before and after low energy impacts

[[abstract]]© 1999 Elsevier - The effects of laminate thickness on the tension-compression fatigue behavior of [0/45/90/-45]ns (n = 2,4,6) T300/976 carbon/epoxy composites damaged by low-energy impact have been investigated. The penetration impact properties and the residual tensile strength under various low-energy impacts were tested. The initial slope during penetration impact reveals that the thicker laminate has a higher stiffness than the thinner one. Moreover, the results also show that the total energy required to penetrate the composite is not proportional to the thickness. The static tensile strength measurements and tension-compression fatigue tests at various stress levels were also carried out on the impacted and unimpacted laminates. The median-rank method and Weibull distribution function were applied to predict the failure probability of the composites under given applied loading and fatigue cycles. The relationship between stress levels and fatigue life (S-N curve) was established and reductions in fatigue life of the impacted laminates at various stress levels were compared. The different slopes of the S-N curves imply that different fracture mechanisms may occur, depending on the laminate. The S-N curves of the composites with different thicknesses were also compared. Ultrasonic C-scanning was used to examine the damage zones in composites subjected to various impact energies and fatigue loadings.[[department]]電機工程學