Abstract
The real weld toe geometry is generally not mathematically perfect, resulting in obvious stress concentration effects, both on the weld section and along the longitudinal direction of the weld toe. The true stress-strain state at the local weld toe directly affects the fatigue performance and behavior of the welded structure. Therefore, a Fiber Bragg Grating (FBG) sensor based method for testing the cyclic strain at the weld toe was proposed. Cruciform welded joints were fabricated as specimens on which FBG sensors were arranged at several characteristic points along the weld toe curve. Strains at all the characteristic points under cyclic tensile load were measured and recorded, which showed the proposed measuring method could accurately obtain the complete local strain time histories along the weld toe. The strain time histories clearly reflected the cyclic hardening phenomenon in the early stage and the plastic yielding phenomenon in the final stage. Furthermore, based on the cyclic stress-strain constitutive model of the weld material, the stress-strain response curves of all the characteristic points were drawn. Combined with the fatigue fracture morphology, the mechanism of the unsynchronized initiation of the multiple cracks in the weld toe was investigated.
Highlights
Welding is one of the most common methods in manufacturing for the joining components
The results showed that the longitudinal discontinuities along the weld geometry have significant influence on the fatigue performances of the weld joints
All the three cracks have crack fronts with semi-elliptical shape, whose centers correspond to the crack initiating positions. Relating these three positions with the weld toe geometry captured before testing, it can be seen that three cracks were all initiated in the positions with a larger stress concentration factor (SCF)
Summary
Welding is one of the most common methods in manufacturing for the joining components. It has the main advantages of simple structure, easy process, low costs, superior performance and high reliability. Engineering application shows that welded structures are prone to develop fatigue cracks under cyclic loads. Once the cracks appear and the welded structure can’t be repaired in time, it will probably cause vital damage. A great deal of research [1,2,3,4,5] has shown that the fatigue performance of welded structures mainly depends on the type of weld joints and the loads. Fatigue cracks often appear in the local position of the weld, especially at the stress concentration position along the weld toe. It is significant to understand the stress-strain state and its response behavior at the weld toe of the welded joint to accurately predict the fatigue life of the welded structure, enhancing the fatigue performance of the welded structure and improving the welding procedure
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