Rate Dependence and Short Term Creep Behavior of Pmr-15 Neat Resin at 23 and 288-C

This research focuses on experimental investigation of rate-dependent behavior and short-term creep of PMR-15 neat resin at 23 and 288 C. Effect of loading rate on monotonic stress-strain behavior was explored in monotonic tests at constant stress rates of 0.75, 0.075, and 0.0075 MPa/s at 23 and 288 C. In addition, effect of prior stress rate on creep behavior was explored in creep tests preceded by uninterrupted loading to a target stress. At each temperature three creep tests were conducted for a given stress level, where loading rate was changed from test to test. Creep stress levels were 30 and 25 MPa at 23 and 288 C, respectively. Also, the effect of stress and strain at the beginning of the creep period was studied in stepwise creep tests, where specimens were subjected to a constant stress rate loading with 1800 s creep periods at 5 MPa stress intervals. Specimens were loaded to a maximum stress then unloaded to zero stress, with creep periods during loading and unloading. Finally, the effect of loading rate was studied in recovery tests where specimens were monotonically loaded to 30 MPa and unloaded to zero MPa, then recovered for 12 hours.