Plastic Pipes Conference Association # 1995 Edinburgh
Van der Grinten, Wichers-Schreur
Hydrostatic pressure testing 1s still the established method in evaluating the performance of plastics pipes. However, the introduction of new plastics materials with greatly improved properties causes hydrostatic pressure failure times to increase considerably. Evaluation of a new material delays introduction onto the market. Thats why fast and accurate test methods are needed. Several concepts have been developed, such as the Notch test, Cone test and PENT test. Further, application of fatigue loading for long term performance tests may also accelerate evaluation.
To apply fatigue loading in evaluating long term performance under constant load conditions the relationship between fatigue and static performance must be known. At GASTEC extensive research has been carried out to analyse this relationship. Three types of polyethylene have been considered. The effects of parameters describing the loading conditions and thus goveming fatigue crack growth, like the stress intensity factor K, AK, frequency and temperature, were analysed. By reducing AK results were extrapolated to static conditions.
AK is the principal parameter describing the loading conditions. Ranking of materials based on fatigue results may change with test temperature. At this stage it is not possible to relate fatigue crack growth to static crack growth.
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