Damping as measure of damage in composites

Abstract

The increase of damping with damage induced by static and fatigue loading of a glass fiber reinforced composite has been measured and is shown to be greater than the corresponding decrease in stiffness. A simple test rig was designed to measure damping and was calibrated using aluminum beam specimens. The loss factor for undamaged specimens was measured for 0° , 15°×, 30°, 45° fiber orientations and was found to be independent of the strain amplitude up to 0.04 per cent strain. Damage was induced by static and cyclic preloading. Static preloading was done at 50, 60, 75, 85 percent of the fracture strength while cyclic preloading was carried out at 50 percent of the fracture strength for 1, 5, 10, 25 cycles. Both types of preloading increased the specimen loss factor. For comparable levels of preloading, the loss factor increased in the order of 0°, 15°, 30°, 45° fiber orientation; for a given fiber orientation, the loss factor was more for greater number of cycles and level of prestressing.