STRESS-STRAIN-TIME DIAGRAMS, INCLUDING FAILURE ENVELOPES, FOR HIGH DENSITY POLYETHYLENES OF DIFFERENT MOLECULAR WEIGHT.

Abstract

The creep behavior of polyethylene bars under uniaxial loading can be categorized as one of two types. One type occurs for relatively high stresses where after some time necking takes place as a result of plastic flow, and the other occurs for small stresses where the material fractures at small deformations due to crack formation and growth. The latter type of behavior was discussed in the previous paper, where the influence of the ambient environment was also considered. In the present work, the emphasis is on the first type of behavior, where uniaxial creep data are presented for several high density polyethylenes of different molecular weight. Depending upon the molecular weight, there exists a narrow region of stress for which one can obtain extension ratios of up to 25 (at 296K) before fracture occurs. The mechanical properties of the highly drawn material are also discussed.