Residual strength in notched composite materials

Abstract

The main objective was to understand the stress concentration factor of fatigue damage for centrally notched composite laminates of various lay-ups in the proportion of 45, −45, 90 and 0 deg plies. The application of fatigue stress concentration factor was used to predict the residual strength. The Whitney-Nuismer (WN) extended point stress fracture criterion and the extended average stress fracture criterion were adopted. The characteristic length is not necessarily a constant; it depends on the shape of the damage zone, the number of applied cycles, the hole radius, etc. The tests were performed at low-frequency tension-tension (T-T) fatigue loading with constant stress amplitude at room temperature. In simple terms, after thousands of cycles, because of the geometric change of a circular hole to the deformed laminate, the stress concentration factor decreases with the increasing number of applied cycles, which is the reason for the increase of residual strength of the notched laminate. The correlation of the residual strength as predicted by the numerical methods and the fatigue stress concentration analysis is found to be satisfactory, in comparison with the experimental data.