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 damag e accumulation in glass fiber woven roving (0/90 degrees) polyester laminat es after prolonged exposure in sea water. Comparisons were made with fatigu e tests of "as-received" laminate under similar loading conditions. Pre-exp osure has been found to substantially reduce the fatigue strength of the co mposite. Acoustic emission monitoring during fatigue testing has shown that the amplitude distribution of the acoustic events shifts from predominantl y low amplitude (40-55 dB), associated with matrix cracking, in as-received specimens, to intermediate amplitude (55-75 dB) associated with delaminati on and debonding after pre-exposure. Optical microscopy of fatigued samples has verified these failure mode changes. The number of recorded high ampli tude 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.