TEMPERATURE AND STRAIN-RATE DEPENDENCE OF YIELD STRESS OF POLYETHYLENE

The yield stress behavior of a range of polyethylene materials which d iffer with respect to their short chain branch content has been studie d. Measurements carried out over a wide range of temperatures have sho wn that there is a sudden transition in the behavior of the yield stre ss at a temperature which is dependent on both the grade of material a nd the applied strain rate. These results are in agreement with previo us results found from analysis of the yield strain behavior. Above the transition temperature the materials all behave in a nonlinear viscoe lastic manner, and the yield process is considered as being propagatio n controlled. Below the transition temperature the materials all behav e in an elastic-plastic manner, and the yield process is considered as being nucleation controlled. Below the transition temperature the tem perature dependence of the yield stress is determined by the thickness of the crystalline lamellae. (C) 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2177-2189, 1998.