TWI Frequently asked questions
For structural analysis, welds are modelled to the extent that is needed for the accurate prediction of the performance of the structure. This statement provides the basis for deciding how a weld should be modelled. For example, most arc welds will have relatively sharp and variable features at the weld toe and these tend to reduce the fatigue strength of welds. However, the sharp features do not mean that a very detailed mesh is needed to predict the local stress distribution. This is because the recommended fatigue S-N curves for welds were generated on specimens having these features, and the test results have been expressed in terms of the nominal stresses for simplicity (see for example, BS 7608 1993). However, if the plates being joined are not aligned, there may be additional secondary bending stresses. The accuracy of cross-weld plate alignment may therefore be important.
It is important that the structural performance parameters are fully understood, and that the method of placing the weld in the model yields an accurate and economic prediction of those parameters.
