Fri, 09 February, 2024
Research undertaken as part of a TWI Core Research Programme (CRP) project has been instrumental in updating a European standard for the mechanical testing of welded joints.
TWI Technology Fellow, Mike Troughton has been involved in the revision of the European Standard, ‘EN 12814-7: Testing of Welded Joints of Thermoplastics Semi-Finished Products. Part 7: Tensile Test with Waisted Test Specimens,’ for the past two years.
The updated standard, which was published on 8 February 2024, was based on a CRP project entitled ‘Improvement of the Reduced Section Tensile Test Specimen Geometry for Assessing the Integrity of Butt Fusion Welds in Polyethylene Pipes.’
The issue with the old standard was that it defined a single specimen geometry for all joint thicknesses. However, as the specimen thickness increases, the measured ductility of the joint in the test decreases, meaning that the test was less capable of distinguishing between joints of different quality in thick-walled pipes or sheets.
The CRP project used design of experiments (DoE), finite element analysis (FEA) and experimental trials to determine the effect of specimen geometry on the failure mode and measured energy to break in butt fusion welds in high density polyethylene (HDPE) pipes and sheets. Based on the results of this study, TWI proposed three different geometries for different ranges of specimen thickness as well as proposing that, for thicknesses greater than 30mm, the specimen is cut into two or more equal slices such that the thickness of the slices is less than 30mm. These recommendations were incorporated into the revised European standard.
This provides another example of how our expertise and experts are benefitting not just our Industrial Members, but also industries as a whole on an international level.
You can read a short case study about the CRP work, here.