Notch sensitivity of polymers

Abstract

AbstractThe influence of notches on the static tensile strenght, low‐cycle fatigue strength, and creep rupture strength was investigated for selected polymeric materials. This investigation was prompted by the unusual phenomena of necking and notch strengthening observed in some glass fiber reinforced plastic materials. Two types of epoxy resin, polymethyl methacrylate and polycarbonate, were studied under static tensile loading. Three sizes of semicircular symmetrical side notch on flat specimens were investigated. It was observed that one of the epoxies was very notch sensitive, while the other exhibited significant (and maximum, out of all the polymers tested) notch strengthening in tensile loading. Perspex and polycarbonate showed a small notch sensitivity for the smallest and intermediate notches but notch strengthening for the biggest notch. The epoxy resin which exhibited notch strengthening was also tested with different percentages of hardener; for the biggest and the intermediate notches, there was a notch strengthening effect and unnotched as well as notched tensile strength showed a peak around 14% hardener. The epoxy which exhibited notch strengthening in tensile loading was next tested in low‐cycle fatigue and creep loading. The behavior in low‐cycle fatigue and creep loading was remarkably similar: it was found that for this polymer, the notch sensitivity was small in the case of the smallest and intermediate notches, whereas there was a significant notch strengthening effect in the case of the biggest notch. It is recommended that notch‐strengthening behavior be added to the other criteria for the selection of matrices for composite materials.