- Use design of experiments (DoE) and finite element analysis (FEA) to predict the optimal reduced section specimen geometries, in order to generate ductile failures in both parent pipe and good quality BF joints, and minimise the elongation in the loading holes during the test, for all pipe wall thicknesses, and verify these geometries experimentally
- Determine the effect of specimen thickness, on the value of energy to break per unit cross-sectional area (CSA), using the above modified specimen geometries
In order to improve the geometry of the reduced section tensile test specimen defined in EN 12814-7, this project used two different approaches.
Firstly, tensile tests were carried out on specimens cut from unwelded sheets of HDPE, where the specimen geometry parameters were varied based on a DoE approach. Secondly, the stress field in the specimen was modelled during the tensile test using FEA for different geometry parameters (Figure 2).
To verify the improvement brought about by the DoE and FEA results, tensile specimens with the original geometry, and with the modified geometries, were machined from both BF joints in HDPE pipes of different diameters and wall thicknesses, and from the pipes themselves, and tensile tested to compare their tensile properties and fracture modes.