Ultimate strength and failure modes for fillet welds in high strength steels

A study has been carried out on the effect of strength mismatch in weld metal and penetration ratio on the ultimate strength capacity of fillet welds and their failure modes. The ultimate strength capacity evaluated with nonlinear Finite Element Analysis (FEA) and testing is compared with the ultimate strength capacity predicted by standards: Eurocode3, BSK 07 (Boverkets handbok om StålKonstruktioner) and AWS (American Welding Society) D1.1 Structural welding code-Steel. Test results are used to establish correct material properties, to be input into the finite element model. A criterion for selection of consumables has been developed, when two different grades of high strength steels are to be joined. The results show that fully penetrated joint with under-matched filler material is more ductile and the ultimate strength capacity of base plate can be achieved. It is observed that joints with under-matched filler material are more sensitive to penetration ratio. The test data correlates reasonably well to the results predicted by FEA software and design codes. It is also concluded that joint preparation has an effect on the ultimate strength capacity of the joint.