Effect of Non-Uniform Material De-Cohesion on Crack Initiation From Notches in Crosslinked UHMWPE

Ultra High Molecular Weight Polyethylene (UHMWPE) has been successfully used as a bearing material in total joint arthroplasty for the last 4 decades [1] but about 5%–10% of the implants undergo revision surgery in the first 10 years of implantation [2]. Crack initiation from a stress-concentration design feature (e.g., a sharp corner of a locking mechanism on an acetabular component) has been observed to lead to catastrophic failure in-vivo [3]. Therefore, it is important to understand crack initiation from clinically relevant notches to mitigate the risk of component fracture. UHMWPE is a semi-crystalline polymer and little is known about the physical mechanisms governing crack tip phenomena. The time dependent theoretical expression of fracture mechanics indicates that the critical fracture energy (J_c) varies with crack initiation time (t_i) with an exponent ‘n’ (Equation 1).