Previous work by the authors has indicated that crack behaviour in PMMA (and thus probably in other materials as well) shows a secondary dependence on the degree of in-plane stress biaxiality, in addition to its established primary dependence on K~, the elastic stress intensity factor. Data published here shows the crack-length dependence of a parameter expressing the degree of stress biaxiality inherent to a number of standard specimen geometries. This should help to determine to what, if any, extent a given material's sensitivity to stress biaxiality is responsible for K~-independent variations in crack behaviour between specimens.
A detailed description of a new numerical method for the solution of dynamic fracture problems is presented. The method employs finite volume discretization of the equilibrium equations.The present work considers the analysis of rapid crack propagation (RCP) in two-dimensional geometries only. The simulation of steady-state RCP in a peeling-strip geometry, and an economical approach which allows the calculation of the crack driving force from a 'snapshot' computation of the displacement field are described. Also presented is the modelling of transient RCP in single edge notch tensile specimens, based on a fixed-mesh 'node release' technique and a 'holding back' force concept. It is shown that finite volume results are in very good agreement with both analytical and finite element predictions. The accuracy, simplicity and efficiency of this novel method are also demonstrated.
Conventional tensile testing applied to high density polyethylene can lead to erroneous impressions of the tensile response of the material due to a local reduction in cross section of the sample. Several workers have developed novel tensile testing techniques to measure the response of a small element as it deforms. The true stress true strain curve that results describes tensile deformation of the material in a geometry‐independent manner. Here, results from previous workers, together with some of our own, are interpreted in terms of the Haward‐Thackray spring‐dashpot model, in which the spring defines a strain hardening process according to the theories of high elasticity and the dashpot describes a strain‐independent viscous process. The effects that temperature, strain rate, and molecular mass have on each process are investigated. For a pipe‐grade, modified high density ethylene copolymer, sufficient data have been measured to interpret the effects of strain rate and temperature in accordance with an Eyring flow process, where the parameters for the two mechanisms are found to be similar.
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