Fatigue delamination propagation: Various effects on results

In this investigation, three subjects are considered. First, the effect of the human factor is examined. In carrying out analyses of fatigue delamination propagation tests on laminate composites, the delamination length must be measured. The human effect on measurement of the delamination length (Formula presented.) by different investigators is discussed. A limited influence of the human factor on the measurement of the delamination length (Formula presented.), as well as on delamination propagation rate (Formula presented.), is observed in this study. Secondly, the paper proceeds to discuss the influence of the (Formula presented.) ratio on the fatigue delamination growth rate. It is found that a higher rate of crack/delamination propagation is associated with lower (Formula presented.) ratios which appears to contradict conventional wisdom. This behavior is confirmed in tests. Thirdly, a comparison between the fatigue propagation rates of two material systems is considered. It is concluded that the energy release rate used to assess these materials should not be normalized.