Stress and energy release rate analysis of cross-ply carbon fiber-reinforced plastic laminate with transverse cracks subjected to ultrasonic vibration using a variational approach

Application of carbon fiber reinforced plastics (CFRP) to structures that are subjected to increasingly high numbers of cyclic loads is expected to expand, so evaluation of fatigue properties up to the very-high cycle regime is essential to prove their long-term reliability. Conventional fatigue testing is not practical for such conditions owing to the excessive time required; ultrasonic fatigue testing, which can be performed at a frequency of 20 kHz, is an effective alternative. Stress distribution in ultrasonic fatigue testing differs from that in conventional fatigue testing because the specimen is resonated. The stress distribution of cross-ply laminates with transverse cracks subjected to resonance was calculated using a variational approach. The energy release rate was calculated based on the results of a previous study on transverse crack initiation. The results of the stress analysis are in good agreement with those of finite-element analysis. Quantitative evaluation of transverse crack initiation was also conducted.