Short-term creep and recovery behavior of medical grade ultra-high molecular weight polyethylene (UHMWPE)

Purpose: In this study, short-term tensile creep and recovery behaviors of medical grade ultra-high molecular weight polyethylene (UHMWPE) were investigated to contribute deformation behaviour of UHMWPE components in knee and hip prosthesis during daily life activities of patients. Design/methodology/approach: Tensile test specimens were machined from compression molded UHMWPE sheets having commercial brand name: Chirulen 1020 and they were prepared according to ASTM 527-2. The tensile creep tests were performed at constant stress levels of 5, 9, 13, 18 and 21 MPa as long as 1 hour for each test. Then, the specimens were allowed to recover unloaded for 1 hour. Automatic extensometer was used to measure the deformations precisely for each test. Findings: Results show that creep rate linearly increased with increasing the stress levels. Permanent deformations were observed after recovery. Recovery of the material became difficult with increasing the applied load at intended time interval. Research limitations/implications: UHMWPE components used in prosthesis have been subjected to complex loading conditions during service life. Polymeric materials show the viscoelastic material properties like strain rate sensitivity, relaxation, creep and recovery at room temperature. Because of the viscoelastic material properties of the UHMWPE, it makes difficult to predict the failure of the UHMWPE components in hip and knee prosthesis. Therefore, deformation behavior of medical grade UHMWPE should be investigated in many different loading conditions. Practical implications: Medical grade ultra-high molecular weight polyethylene (UHMWPE) have been used commonly in total hip replacements as acetabular cup and in total knee replacements as tibial insert since early 1960s.