Effect of Circular Hole Discontinuities on Crushing Characteristics of Combined Geometry Shells of Tailor Welded Blanks

In this research work, two-stage drawing was employed to fabricate combined geometry shells with hemispherical and cylindrical segments using two types of laser welded blanks, namely similar thickness (LWBs) and dissimilar thickness (LWTBs) of extra deep drawing steels. Four diametrically opposing circular holes of 4 mm and 8 mm were drilled in the cylindrical portion. These shells were quasi-statically crushed between two flat platens to investigate the effect of the presence of hole on crush characteristics such as collapse modes and load–displacement response. The collapse of LWTB shells started with an inward dimple in the hemispherical section and followed by uneven and partial folding of the cylindrical section due to the non-uniform thickness variation across the weld zone. However, it was identified that the presence of 8 mm holes promoted progressive folding with a uniform load–displacement response, while uneven and partial folding was observed in shells with 4 mm holes. The use of Stoughton non-associated flow rule (S-NAFR) in finite element modeling predicted the non-uniform thickness variation and earring profile of the LWTB shells better than Hill48 model. Also, the load–displacement response and modes of collapse during the crushing of all the shells were predicted well using the S-NAFR model. Based on the above findings, it was perceived that the circular holes could be inserted as discontinuities in LWTB shells to suppress the effect of non-uniform thickness distribution on the crushing characteristics.