Abstract
The influence of elastic modulus of weld matal on fatigue strength of welded joints was studied for boxing weld joints under tensile stress. Boxing weld joints with weld metals of carbon steel (elastic modulus: 206GPa), austenitic stainless steel (193GPa) and Invar (150GPa), an Fe-36% Ni alloy, were tested. Furthermore, elasto-plastic finite element analyses (EP-FEA) were carried out on fillet weld joints with weld metals of different elastic modulus to study the strain distributions in the vicinity of the weld toe.
The results are summarized as follows:
(1) Fatigue strength of welded joints with weld metal of Invar is higher than those of carbon steel and austenitic stainless steel. Enhancement of fatigue strength of joints with Invar weld is especially large at high stress ranges for crack initiation life.
(2) The lower elastic modulus of weld metal of fillet weld joints is, the smaller the maximum principal strain in the vicinity of fillet weld toe by EP-FEA is. This phenomenon is explained by the yielding in stress concentration region of weld metal due to the displacement-constant condition in the vicinity of weld toe.
(3) The result of EP-FEA shows that lowering the elastic modulus of weld metal to decrease strain in the vicinity of weld toe is more effective in higher region of nominal stress applied to fillet weld joints. This tendency corresponds to the experimental results of boxing weld joints of Invar.
(4) According to the EP-FEA, mechanical behaviors in the weld toe of joints with weld metal of low elastic modulus qualitatively corresponds to that of the model in which bonded material of weld metal and base metal (and HAZ) in series with a notch is loaded under constant displacement.
