Experimental investigation of the very high cycle fatigue of GFRP [90/0]s cross-ply specimens subjected to high-frequency four-point bending

In contrast to low cycle and high cycle fatigue, very high cycle fatigue of fibre-reinforced composites has only been explored in part. Knowledge of degradation behavior, damage mechanisms and phenomenology of damage initiation and growth in the range up to 108 cycles and beyond is rare. A special high-frequency four-point bending test rig has been set up to circumvent common problems such as specimen heating. As tests can be conducted in a frequency range between 50 and 80 Hz, load cycle numbers of up to 108 are reached within acceptable testing times. In the presented test series, the very high cycle fatigue behavior of a [90/0]s glass fibre-reinforced laminate is tested at six different load levels. The use of online transmitted light photography and stiffness monitoring provides the correlation of stiffness degradation with transverse cracking and delamination. The effect of load level is examined. Damage growth differs for high- and low load levels. At low loads, degradation is shifted to higher cycle numbers. Delamination onset is delayed by slower crack growth in thickness direction. At the lowest loads, cracks initiate marginally indicating a threshold for transverse cracking in fatigue.