The use of crack layer theory to predict the lifetime of the fatigue crack growth of high density polyethylene

In the case of high density polyethylene (HDPE), the fatigue crack propagates in a discontinuous manner, which can be observed by distinct striations. In this article, fatigue crack growth (FCG) experiments were conducted on two grades of HDPE pipe with compact-tension (CT) and cracked round bar (CRB) specimens. The effects of the stress ratio (R-ratio) which is defined as the ratio of minimum stress and maximum stress of fatigue loadings and the frequency on FCG behavior were experimentally studied. Although FCG rates showed a great dependence on the R-ratio in terms of the range of the stress-intensity factor, the effect of the frequency may be considered to be significant in the low crack growth region. In addition, these experimental data were employed for predicting the lifetime on the basis of the crack layer (CL) theory. Only a few steps of FCG are needed to determine all necessary parameters for CL theory, and the FCG behavior can be reconstructed based on a computer program that has been developed for the application of CL theory. The predictions from this program accord with experimental data.