DEVELOPMENT OF A MODEL FOR LOW-CYCLE FATIGUE ASSESSMENT OF 347 SS BUTT-WELDED JOINTS

This contribution deals with the low cycle fatigue behavior of butt-welded joints of austenitic stainless steel (1.4550, type 347). The focus is on the problem how to model these welded joints adequately with the objective of its assessment. Thereby, the differences between as-welded and machined weld are considered, in addition. The considerations presented here are based on previous investigations reported by Lang et al. [10]. Therein, a new approach was proposed in order to determine the local strains and the LCF relevant influence of the butt weld. It is based on material mechanics and includes an accurate modeling of the real weld geometry based on 3D scans with very high resolution. Originating from this detailed model an idealized model is derived that takes into account significant parameters of a butt weld. In addition, the inhomogeneity of the weld is considered in the model, now, that has previously been ignored. Therefore, the part around the weld was partitioned in material zones according to their hardness. The underlying hardness measurements revealed significant influences of the load history. The results of the numerical simulations based on the new model are compared to them of the scan-based model and the measuring results from related fatigue tests. Considering further fatigue influences as the size and surface roughness the new approach is intended to be adopted in a global design and calculation concept for low-cycle fatigue assessment of buttwelded joints applicable for normal users.