EXPERIMENTAL INVESTIGATION OF FATIGUE-CRACK GROWTH-BEHAVIOR AND DAMAGE MECHANISMS OF FIBER METAL LAMINATES UNDER UNIAXIAL AND BIAXIAL LOADING

The response of the aramid reinforced aluminum-epoxy-laminate to uniaxial and biaxial fatigue loading has been investigated. The fracture process in the laminates propagates mainly in the form of cracks in aluminum layers, delaminations between the resin-rich and fiber-rich prepreg layers, splitting in prepreg layers and fiber fracture. Ultrasonic microscopy has been used to evaluate the shape and size of the damage zone. The ultrasonic images have been calibrated by means of SEM and optical microscopy of the laminates with sequential removal of the layers. Microscopic examination reveals a direct correlation between delamination, fiber fracture, and fatigue crack growth in the aluminum layer. The results of this investigation strongly suggest that the laminate resistance to tension-tension biaxial fatigue Is superior to that under uniaxial loading conditions.