The R1MS approach

Even if two seam welds are created using the same manufacturing process, there will always be variations in the weld geometry. The following figure shows these variations for two seam welds, used to connect 1 mm metal sheets. Both seam welds have a created by the same manufacturer and have the same gap, width, height and melting of the lower sheet. Next to statistical scatter in the weld geometry, there is also a scatter on material properties, for example, the SN-curves of the welded material. Because it is impossible to create a numerical model that is able to account for all these variations, the local approach was refined in order to account for the "worst case" scenario, in which the mean and scatter of the above parameters are taken into account. This translates to an RxMS finite element model with a "nominal" weld geometry, like it was defined during the design of the seam weld. The statistical variations such as the mean and scatter bands are then taken into account by SN-curves, created for the RxMS method. [1]

Weld Geometry Variations - 1 mm Sheets, Same Manufacturer, Gap, Width, Height, Melting of the Lower Sheet

The initial version of the RxMS models, that already included the mean and scatter concept, was published in 1991. [2] At that time, the development of this method was focused on seam weld applications with a sheet thickness varying between 8 and 40 mm, which was at that point more-or-less the standard in industrial engineering. For this type of applications fine seam weld models with nominal weld geometry of radius R = 1 mm at the weld root and weld toe notches were developed. These first models were given the name R1MS. The R1MS method was verified in a large experimental project that compared the results of more than 250 fatigue life experiments with the equivalent data of the R1MS approach. The results were very good which resulted in the R1MS approach becoming a part of the IIW Recommendations. [1]

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