Some aspects of the mechanical response of BMI 5250-4 neat resin at 191°C:: Experiment and modeling

The inelastic deformation behavior of BMI-5250-4 neat resin, a high-temperature polymer, was investigated at 191 degrees C. The effects of loading rate on monotonic stress-strain behavior as well as the effect of prior stress rate on creep behavior were explored. Positive nonlinear rate sensitivity was observed in monotonic loading. Creep response was found to be significantly influenced by prior stress rate. Effect of loading history on creep was studied in stepwise creep tests, where specimens were subjected to a constant stress rate loading followed by unloading to zero stress with intermittent creep periods during both loading and unloading. The strain-time behavior was strongly influenced by prior deformation history. Negative creep was observed on the unloading path. In addition, the behavior of the material was characterized in terms of a nonlinear viscoelastic model by means of creep and recovery tests at 191 degrees C. The model was employed to predict the response of the material under monotonic loading/unloading and multi-step load histories. (c) 2007 Wiley Periodicals, Inc.