Abstract
Residual stresses in welded joints are supposed to change during fatigue loading. Residual stresses can be, depending on the loading conditions, relaxed as well as build up and they can be affected by fatigue crack growth. Furthermore residual stresses are supposed to affect the fatigue strength of welded steel structures. However, tensile residual stresses decrease and compressive residual stresses increase the fatigue strength. This residual stress effect on the fatigue strength is mostly explained with different crack propagation rates.The presented work is on welded longitudinal stiffeners, made of unalloyed fine grained carbon steel, with different fatigue crack lengths in which residual stresses have been determined. The residual stress measurement was conducted using Neutron diffraction. The results of the diffraction measurement show that the initial tensile residual stresses near the weld toe are, caused by phase transformation at low temperatures, below the base materials yield strength. Tensile residual stresses in the order of the yield strength can be found below the materials surface. These areas of high residual stresses are moving with the propagating crack tip through the specimen during fatigue loading.
Highlights
Welding is commonly used for joining of cyclically loaded steel or aluminum structures
The crack length and the experimental S-N data indicate that the “medium crack” sample was at approximately 50 % of the expectable life time and “long crack” sample was at approximately 75 % respectively
Residual stress fields have been determined in steel plates with longitudinal fillet welded attachments in different conditions; “as welded”, “medium crack” and “long crack”
Summary
Welding is commonly used for joining of cyclically loaded steel or aluminum structures These structures must be investigated regarding their fatigue strength. The crack propagation rate is a measure of fracture mechanics and often investigated in small scale C(T) (compact tension) samples This sample type is fairly small and macro residual stresses are rather low [2]. Samples with higher residual stresses, for instance welded steel plates, allow studying residual stress effects on crack propagation in larger scale. Such investigations on welded plates have been published by different authors, examples of which are given in [1,2,3,4]
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