Effect of the crack layer theory parameters on the discontinuous slow crack growth of high density polyethylene under fatigue loading

For engineering thermoplastics, particularly high density polyethylene (HDPE), the crack layer (CL) theory is an effective proposition for modeling slow crack growth and predicting their lifetime. Nevertheless, the associated excessive input parameters needed in its implementation sets a difficulty for its use. Therefore, an understanding of the role of each parameter and how they affect the CL growth is needed. The effect of the parameters has been studied in the past, however, under creep conditions only. Their effects under other loading conditions, e.g., fatigue, and geometries, e.g., compact tension (CT) specimen, is still unclear. For instance, increasing the natural drawing ratio λ was found to non-linearly reduce failure time t_f, whereas a rise in the drawing stress σ_dr increased t_f which correlates logarithmically with the loading frequency f. Furthermore, t_f was found to increase with the transformation energy γ^tr, specimen thickness B, plane stain elastic modulus E^′, drawing stress σ_dr, characteristic time t^∗, and the specific fracture energy γ₀. Therefore, outcomes of this work extend the applicability of the CL theory in the design and lifetime prediction of various industrial products within oil and gas, nuclear, automotive, and aerospace.