Fatigue damage and fatigue limits of a GFRP angle-ply laminate tested under very high cycle fatigue loading

In contrast to fatigue in the low and high cycle fatigue range, the so-called very high cycle fatigue range (>107 cycles) has only been investigated to a minor degree. As very high cycle fatigue testing is challenging in many regards, a special high-frequency four-point bending test rig was developed, set up and validated previously. In this recent study, comprehensive experimental results of an angle-ply laminate tested up to 1.5·108 cycles are presented. In addition to initiation and progression of fatigue damage, stiffness degradation and final failure are investigated at seven load levels. Whereas strain and cycle number show the typical logarithmic dependency in the HCF range, the SN-curve is found to flatten out at lower loads due to slower delamination growth. Neither delamination growth nor final failure are observed at the lowest load level indicating the existence of a delamination threshold load and consequently a fatigue limit. Crack initiation behavior is related to results of a cross-ply laminate by means of a static failure criterion-based master curve approach. Furthermore, the effects of test frequency and specimen heating are investigated.