Method Of Multiaxial Fatigue Life Estimation Of Welded Structures Based On Critical Plane Method

Most of the welded components are subjected to multiaxial loading in the field of naval architecture and ocean engineering. Solely concentrating on the study of simpler uniaxial loading is one of the main reasons that accidents of fatigue and fracture cannot be controlled effectively. However, multiaxial is more closed to practice and the researches on multiaxial can also enrich the knowledge of fatigue’s damage mechanism and failure process. Although the method of mutiaxial is not popular in ship and ocean engineering field, the use of this method must be a trend in the future.The paper aims to analyze the complexity of cyclic stress at the welded joints and comes up with an accurate method of multiaxial fatigue estimation which is more convenient for practice use and more closed to the essence of fatigue. This method which based on the theory of critical plane, explains the physical significance using cyclic deformation theory of monocrystal and conception of crack initiation and comes up with the main stress component which influences the crack initiation and propagation in initiation phase. The present paper estimated the multiaxial fatigue life of the flange-tube specimen made of steel and aluminum under different cyclic loadings (bending, torsion, combination of bending and torsion including in-phase and90degree out-phase) by finite element method and compared the estimating results with experimental results to suggest that this fatigue life estimation technique is accurate and reliable.With the combination of the equivalent hot spot stress method and the Modified Wohler Curve Method, the assessment of multi-axial fatigue life is more convenient and more dependable to be predicted under the given loading path.