Stochastic Fatigue Damage Accumulation of FRP Laminates and Joints

Abstract

Results are presented from a study on fatigue damage accumulation in fiber-reinforced plastic coupons and joints. The main objective of the study is to investigate the effectiveness of the Palmgren-Miner linear damage accumulation model in predicting the fatigue lives of FRP structures under stochastic loading histories. The coupon specimens used in the study are configured four ways: with the laminate laid up in two loading directions (0/90° and ±45°), and with the load transferred by two types of bearing (passive and active). The joint specimens considered represent bonded, bolted, and bonded-bolted butt-strap configurations. The results of the constant-amplitude fatigue tests are fitted to two types of S-N curve models: power-law and exponential. Variable-amplitude fatigue tests using narrow-band stochastic stress histories with various root-mean-square stresses are carried out. Rayleigh approximation formulas corresponding to both types of S-N curves are used to predict the fatigue lives based on the S-N curve and loading parameters. The analytical fatigue life predictions are compared with the experimental results. It is shown that the analytical predictions may overestimate or underestimate the actual fatigue lives, depending on the specimen configuration and the root-mean-square stress level.