On the Cumulative Fatigue Damage in Roving Glass Cloth FRP

Abstract

One and two-stress level fatigue tests have been conducted to investigate the fatigue properties of glass fiber reinforced plastics, especially the relation between cumulative fatigue damage and residual strength. The materials used for the experiment were FRP laminates made of polyester resin and plain woven roving glass cloth. The tests were performed in repeated tension with the minimum value of cyclic stress equal to 5 percent of the cyclic stress amplitude.
The tensile strength of the material under fatigue loading decreased with increaing the number of stress cycles, and fatigue failure occured when the residual strength became equal to the maximum value of cyclic stress.
The reduction of the residual strength at a given stress level has been determined as a function of number of cycles. The experimental results show that for the high-low stress cumulative damage test the Miner's sum, (n₁/N₁)+(n₂/N₂), is greater than unity and for the low-high stress test less than unity.
These observations agree both qualitatively and quantitatively with the predicted values of fatigue lives based on the strength reduction theory.