Use of acoustic emission to characterize corrosion fatigue damage accumulation in glass fiber reinforced polyester laminates

The acoustic emission technique has been used to characterize fatigue damage accumulation in glass fiber woven roving (0/90 degrees) polyester laminates after prolonged exposure in sea water. Comparisons were made with fatigue tests of "as-received" laminate under similar loading conditions. Pre-exposure has been found to substantially reduce the fatigue strength of the composite. Acoustic emission monitoring during fatigue testing has shown that the amplitude distribution of the acoustic events shifts from predominantly low amplitude (40-55 dB), associated with matrix cracking, in as-received specimens, to intermediate amplitude (55-75 dB) associated with delamination and debonding after pre-exposure. Optical microscopy of fatigued samples has verified these failure mode changes. The number of recorded high amplitude events (greater than or equal to 80 dB) associated with fiber fracture is the same in both cases, which indicates that the glass reinforcement is unaffected by pre-exposure.