Improvement of fatigue strength in heavy steel constructions through arc brazing

The possibility of arc brazing of non-loaded attachments with the filler material CuAl7 instead of welding on cyclically stressed steel constructions was investigated. The notch effect under cyclic loading was significantly reduced for non-loaded arc brazed plates on base material of S355 and therefore the fatigue strength improved. The specimens did not show sensitivity to changes of the thickness and size of the non-loaded arc brazed plates during fatigue testing. Furthermore, no negative thickness effect by increasing the thickness of the base material was observed. Microstructural analysis showed that the dimension of the heat affected zone was reduced through reduced heat input and that liquid metal penetration (LMP) occurs in the base metal, which has no negative effect on fatigue strength. Measurements of residual stresses in the weld / braze toe area showed that tensile residual stresses have not significantly been reduced, which can be attributed to comparable reactional forces of the copper alloy during cooling through a higher coefficient of thermal expansion. Numerical analysis showed that compared to a welded detail, the stress concentrations on the weld toe of the arc brazed fillets drop significantly due to the lower Young's Modulus of the alloy. The static testing of the load bearing capacity of arc brazed attachments showed that high tensile and shear stresses, which are comparable to the strength of the base metal, can be reached before fracture.