STUDY OF CREEP-BEHAVIOR OF ULTRA-HIGH-MOLECULAR-WEIGHT POLYETHYLENE SYSTEMS

The short-and long-term creep behaviors of ultra-high-molecular-weight polyethylene (UHMWPE) systems (compression-molded UHMWPE sheets and s elf-reinforced UHMWPE composites) have been investigated The short-ter m (30-120 min) creep experiment was conducted at a load of 1 MPa and a temperature range of 37-62 degrees C. Based on short-term creep data, the long-term creep behavior of UHMWPE systems at 1 MPa and 37 degree s C was predicted using time-temperature superposition and analytical formulas. Compared to actual long-term creep experiments of up to 110 days, the predicted creep values were found to well describe the creep properties of the materials. The creep behaviors of the UHMWPE system s were then evaluated for a creep time of longer than 10 years, and it was found that most creep deformation occurs in the early periods. Th e shift factors associated with time-temperature superposition were fo und to increase with increasing temperature, as per the Arrhenius equa tion. The effects of temperature, materials, and load on the shift fac tors could be explained by the classical free volume theory. (C) 1998 John Wiley & Sons, Inc.