Influence of molecular weight on fatigue behavior of polyethylene and polystyrene

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Abstract
Fatigue tests in reversed tension‐compression have been carried out on samples of polyethylene and polystyrene of widely varying molecular weights, extending up to 2, 000, 000. All tests on polystyrene specimens were made at 1600 rpm. For polyethylene, tests speeds had to be reduced to 100 rpm in order to avoid serious temperature effects. For both materials, increasing molecular weight leads to improved resistance to alternating loading. For polystyrene, this improvement in ultimate properties even continued well beyond molecular weight values where Tg, becomes effectively independent of molecular weight. For polyethylene, samples of high molecular weight did not fail even after 107 cycles of alternating loading at a stress level of 3000 psi.