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Material, structural and pressurising fluid models for RCP tests on

 

Fracture # 1995 Edinburgh

The development of pipe-grade materials to resist slow crack growth and ductile rupture has been spectacularly successful. It is a measure of this success that concern with Rapid Crack Propagation (RCP) has increased to the level evident at this conference. Stronger materials encourage the use of higher operating pressures, thinner walls and/or lower operating temperatures : it is important to know which strategy can effectively exploit them without approaching the RCP regime, but this has proved to be quite difficult to predict. This paper surveys progress on three fronts. Firstly, the distinction between impact and RCP resistance has, at least for polyethylene, been clarified by the development of a model which successfully predicts both 'properties' from more basic ones. Secondly, a new computational method has allowed the crack driving force in a pipeline to be computed for small-scale a n d large-scale test configurations, so that fracture resistance data can be used to translate critical pressure results from one to the other. Finally, experiments using water and waterlairpressurised pipes have demonstrated the complex and crucial role of decompression within the contained fluid. The 'decompression length', over which the pressure drops to zero behind a running crack, srrong :y affects  :he crack driving force, so that it is essential to model it accurately.

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