Materials and Their Characteristics
Plastic Pipes Conference Association # 1985 York
Moore, Prediger, Stephenson
Fracture mechanics techniques are applied to UPVC pipe compositions in order to obtain quantitative and credible toughness results. The influence of polymer molecular weight and pipe age-in-service is then examined.
The techniques are also applied to considerations of material toughness and pipe toughness.
Plastics pipes, particularly those manufactured from PVC and polyethylene, have been in service successfully for many years. The continuing interest and activity in predicting the service life of pipe indicate that a full understanding of the numerous factors influencing pipe lifetimes has not yet been achieved. Whilst it would seem reasonable to expect that pipe toughness could be easily measured and directly related to service performance this has proven not to be the case. Nevertheless significant advances in testing techniques and prediction methods have been made in recent years. A sound basis for the consideration of toughness is essential if further progress is to be made. In this paper we consider four aspects of toughness.
- what to measure
- how to measure it
- what might influence it
- how to use it
Fracture mechanics concepts have been established as quantitative methods for measuring toughness (1). They have been applied to a range of materials with considerable success.
Despite the marriage of a linear elastic theory to non-linear viscoelastic materials, fracture mechanics may usefully be applied to thermoplastics. There has been recent progress in the identification of appropriate geometry and size factors in order to achieve objective and valid measurements of fracture mechanics parameters. These ideas are documented in the literature (2,3 ), but because they are an important consideration in this work, it seems appropriate to define the main steps in the argument.
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