Influence of internal temperature development during manufacturing on thick laminates compression fatigue properties

Abstract

Thick laminates (above 6 mm) are increasingly present in large composite structures such as wind turbine blades. Blade designs are based on static and fatigue coupon tests on 14mm thick laminates. However, a thickness effect has been observed, showing significantly shorter fatigue life in thick laminates. Different factors are suspected to be involved in the decreased static and dynamic performance of thick laminates. These include the effect of selfheating during fatigue testing, scaling effects, and the influence of residual stresses due to temperature gradients during manufacturing. This work studies the influence of the temperature gradients during resin infusion on the through-thickness fatigue properties in thick laminates. Coupons from thick laminates cured at different curing rates have been tested in fatigue. The work reports the compression fatigue properties of a thick laminate and relates the results with the curing rate. Safety factors between 1.23 and 1.60 regarding the influence of the curing cycles in thick laminates are reported.