Abstract
AbstractExtensive studies of the creep and recovery behaviour of oriented polyethylene have been undertaken because of the potential engineering applications of high modulus polyethylene fibres and large section oriented materials made by the Leeds die‐drawing process. Two primary requirements are a valid protocol for the practical assessment of the creep behaviour and an adequate formal representation which can provide the basis for a physical interpretation of the creep processes in terms of the structure of the oriented materials.The practical requirements of improved creep performance lead to examination of the effects of molecular weight and copolymerisation on creep and recovery, together with studies of the effects of radiation cross‐linking either before or after drawing. A particular new feature has been the development of a process for cross‐linking in acetylene, where it has been shown that diene bridge crosslinks are produced with very little chain scission.The protocol adopted for assessing creep behaviour is to construct creep strain rate/strain (Sherby‐Dorn) plots which, for highly oriented fibres, show constant strain rates after an initial period. These equilibrium strain rates can be modelled by two thermally activated processes acting in parallel.In recent research these studies have been extended to fibres of lower draw ratio and to isotropic polyethylene. It has been possible to establish links between creep and yield behaviour, and to show that slow crack propagation can be understood in terms of a combination of yield and creep to failure.
Published Version
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