DEFORMATION AND TOUGHNESS OF POLYMERIC SYSTEMS .4. INFLUENCE OF STRAIN-RATE AND TEMPERATURE

The influence of testing speed and temperature on the brittle-to-tough transition of non-adhering core-shell rubber-modified polystyrene-pol y(2,6-dimethyl-1,4-phenylene ether) (PS-PPE) blends was studied. The v alidity of the concept of a network density dependent, critical matrix ligament thickness (ID(c), as introduced in this series and verified mainly by slow-speed uniaxial tensile testing) is demonstrated for not ched high-speed (1 m s-1) tensile testing at different temperatures. T he influence of testing speed and temperature on the absolute value of ID(c) can be quantitatively understood in terms of a strain rate and temperature dependence of the yield stress. The simple model introduce d in part 2 of this series proves to be valid under all testing condit ions studied varying from temperatures of 50 to 150-degrees-C below th e glass transition temperature of the PS-PPE blends. The absolute valu e of the tensile toughness, on the contrary, is a not yet quantified f unction of the test geometry applied and, consequently, cannot be dire ctly derived from a simple strain-to-break argument.