Residual strength of GFRP at high-cycle fatigue

Degradation of the residual strength of a glass-fiber-reinforced polyester composite of a lay-up typical of the wind rotor blade material is studied a t low-cycle fatigue. A gradual reduction of the residual strength is observ ed as expected for GRP, accompanied by an increasing scatter of strength. T he residual strength model based on the strength-life equal rank assumption yields an accurate approximation of experimental data. The strength reduct ion at a stress level corresponding to high-cycle fatigue (N > 10(6) cycles ) appears to correlate Hell with the test results at higher stress levels, which indicates that the strength degradation at the design str-ess level c an be evaluated using low-cycle tests. Assuming that the parameters of the strength degradation model do not depend on the applied stress level, the r esidual strength data obtained in low stress level tests of comparatively s hort duration can be used to estimate the average fatigue life at the same stress thus reducing the total test time.