Weld zone representation during the formability prediction of friction stir welded blanks with similar thickness sheets

摘要

During formability prediction of friction stir welded (FSW) blanks, it is necessary to incorporate nugget zone and heat-affected zone (HAZ) properties separately for better accuracy. In general, it is observed that the weld zone is represented as a single entity, in which only global weld zone properties are implemented. In this work, it is proposed that there is a domain of weld conditions in which the single-zone assumption (nugget and HAZ are modelled without incorporating their individual properties) breaks down and the double-zone assumption (nugget zone and HAZ are represented separately) should be followed. During limiting dome height simulations, a representative base material is considered from the literature with changing nugget zone and HAZ properties. The punch displacement at failure and maximum load are compared between FSW blanks modelled with single- and double-zone assumptions. It is observed that modelling FSW blanks with double-zone assumption plays a vital role for accurate formability prediction. The single-zone assumption is not valid for all the FSW conditions. Both in transverse and longitudinal weld orientations, there are possibilities of multiple domains in which the double-zone assumption is valid. It is found that there exists a relationship between the thickness distribution and availability of single-zone or double-zone models. Whenever the thickness distribution of a particular double zone is closer to the reference case modelled with single zone, it is sufficient to model that weld zone case with a single zone. Double-zone representation is required in cases when the thickness distribution is very different. The domains for weld zone modelling in FSW blanks are sensitive to failure location. Put simply, it is advisable to model HAZ separately, when failure occurs in it. But this is not always the case. It depends on a compromise between the accuracy and availability of HAZ properties.