Fracture Mechanisms and Residual Strength of Fatigue-Damaged FRPP by Means of Acoustic Emission Technique

Fracture mechanisms and residual strength of fatigue-loaded FRPP with notch are studied by means of acoustic emission technique. The maximum AE cumulative event count and the maximum total AE energy increase in the ratio of number of cycles N to number of cycles to failure Nf, N/Nf, and the load at AE initiation and the loads at change of damage mechanisms decrease similarly to the maximum load, although the degree of damage is varied by the stress amplitude. In the case of small fatigue-damage the many resin crackings occur, but in the case of large fatigue damage the damage mode changes from the fiber debonding to the fiber breaking. The microfractographs prove the estimation by AE frequency analysis. It is found that the residual strength of fatigue-damaged specimen is determined by the load ratios Pi/Pi (N) and Pb/P , where the suffix (N) shows the nondamaged specimen, but the reliability of Pi/Pi (N) is poorer than that of Pb/Pb (N).