Elevated-Temperature Fatigue Testing of Laminated Shear and Tension Coupons for Design of Helicopter Rotor Blades

Paper presents results of testing 100 environmentally conditioned coupons subjected to long-term fatigue loading of up to 10 million cycles. Two different layups were studied consisting of glass and carbon fiber-reinforced epoxy-resin material. Coupons were moisture conditioned prior to test and cycled in an enhanced temperature and moisture environment. Objectives are to provide effects of environment, three different material batches, and two types of loading. In addition a measure of damage growth or stiffness reduction was performed after every 1,000 cycles. Fatigue data curves are typically reduced to account for hot, wet effects based on static test results. Tests will verify this approach with coupons cycled at an elevated temperature and moisture environment. Conclusions are that environmental effects established during static testing are applicable to fatigue results. It was also observed that stiffness degradation did not occur in coupons subject to a large number of axial tension or shear loadings.