Mechanical behavior of transverse fillet welded joints of high strength steel using digital image correlation techniques

Abstract

Mechanical behavior of 24 lap-welded fillet joints and 20 cruciform fillet joints made of high strength steels (HSS) under tension load is investigated by experimental study. Traditional deformation measurements for transverse fillet weld joints have many weaknesses, which can be solved by digital image correlation techniques (DIC). The strain distribution development over the specimen along the whole loading process were analyzed by using DIC measurement. Test specimens were prepared using four classifications of filler metal and two weld sizes were included in each type of transverse fillet welded specimens. The effect of parameters (e.g. weld size and mismatch ratio) on mechanical properties (e.g. failure modes, fracture angle, ultimate strength and weld ductility) of those two types transverse fillet weld were compared. Due to the softening and other metallurgical effects, cruciform type specimens are more prone to fail around fusion lines than weld metal. Generally, because of the existence of friction force, mean strength of lap-welded specimens are higher than that of cruciform type specimens. The mean ductility of lap-welded specimen is similar to that of cruciform type specimen. Two load-deformation curve features, “rise” feature and “platform” feature, were identified. Most lap-welded specimens have “rise” feature load-deformation curve while most cruciform type specimens have “platform” feature load-deformation curves. Generally, the specimens with “rise” feature load-deformation curve are more likely to suffer sudden fracture. The instantaneous and simultaneous fracture was observed at fracture surface of lap-welded specimen. Joint misalignment has significant impact on the deformation patterns of cruciform type specimens. Based on load-deformation curves of cruciform type specimens, three deformation patterns were proposed. Due to the existence of three deformation patterns, the variability of strength and ductility are much larger than lap-welded joints. Moreover, it is confirmed that EC3 and AISC Specification are conservative for all mismatched filler metals.