Study On The Assessment Methods Of Fatigue Failure In Aluminum Alloy Welded Joints

S-N curves of welded joints made by 3A21 aluminum alloy are studied based on the results of fatigue tests. The influence of the different joint geometries and weld toe radius on S-N curve is discussed by the test result of welded joints. It indicates that the constant m and the fatigue resistance value which is at 2×106 cycles are different from the value recommended by IIW obviously. The fatigue assessment result of aluminum alloy welded joints that is given by IIW S-N curve is conservative. In addition, the different joint geometries lead to the difference of local stress concentration of welded joints, so nominal stress S-N curve is affected evidently. The stress averaging approach (SAA) is one of the local stress approaches. Fatigue behavior of 3A21 aluminum alloy welded joints is assessed by this approach here. It calculates the local stress by the finite element and establishes S-N curve assessed by SAA. It shows that SAA can reasonably assess the fatigue behavior and predict the sites of fatigue fracture of welded joints. The result is conservative. According to Neuber's proposal, the weld toe was regarded as a sharp notch, namely, ρ=0mm and ρ*=0.15mm, which has certain applicability in engineering. With the way, bigger stress will be concentrated in the weld toe, thus the local stress by calculating is bigger than actual one. The weld toe is important to fatigue properties of welding joints and it also leads to the biggest stress among stress concentration zone. The Critical Distance Method (CDM) consists of the Point Method (PM), Line Method (LM) and Area Method (AM). The Point Method (PM) is applied to the fatigue assessment of 3A21 aluminum alloy welded joints for two different joint geometries here. ANSYS software was used to calculate the local stress and S-N curve is established by the result. The influence of the different mesh and joint geometries on the result is discussed. It is shown that PM can reasonably assess the fatigue behavior and predict the sites of fatigue fracture of welded joints. For welded joints, PM local stress ?σ PM is a universal fatigue restraining parameter, the fatigue intension expressed by ?σ PM is independent of the joint geometries. PM is dependent of the FE mesh size. Under the same stress, fatigue life for type C is higher than type D2's, namely, fatigue failure is easier to produce on type D2.