Study On Fatigue Properties Of Butt Welded Joints Considering The Welding Initial Deformation Of Thin Plates

The initial deformation of welding,angular misalignment and axial misalignment are commonly occurred in the thin and slender welded joints.The DNV specification introduces the concept of stress amplification factor considering the influence of the welding defects on fatigue strength.However,the formula for calculating the stress amplification factor recommended by the specification takes only the effect of angular misalignment and axial misalignment into account.That will make the evaluation result inaccurate without taking the influence of the initial deformation of welding into account.Therefore,this paper considers the influence of angular misalignment and initial deformation of welding on fatigue strength,and proposes a new formula for calculating the stress amplification factor.The accuracy of the formula is verified by the experimental data in the literature.Firstly,local angular misalignment is used to represent the initial deformation of welding of the butt joint of thin plate.The calculation model of the stress amplification factor considering the influence of the initial deformation of welding and the angular misalignment is proposed,and the corresponding formula of the stress amplification factor is deduced.By comparing the calculation results of the stress amplification factor formula with the calculation results of the stress amplification factor formula in the specification,it can be concluded that the initial deformation of welding has a great influence on the stress amplification factor.Secondly,Finite element software ANSYS is used to establish a finite element model of a series of butt joints with different welding defects,and the structure hot spot stress of different joints was calculated.By comparing the results of the finite element calculations with the calculated results of the derived stress amplification factor formula,there is a large error in the calculated results of the derived formula.According to the analysis of the stress amplification factor calculation model presented in this paper,the reason for this large error is that the derived formula takes into account the maximum additional bending stress in the calculation model rather than the additional bending stress at the toe of the sheet butt joint.Therefore,the proposed theoretical formula is modified for this problem,and then the modified formula is compared with the numerical analysis result to verify the accuracy of the revised formula of the stress amplification factor.Finally,the fatigue strength of the butt joints of thin plates is reanalyzed based on the calculation formula of the stress amplification factor proposed in this paper.The welded joints have some defects such as angular misalignment,axial misalignment,and the initial deformation of welding.The results show that,it is safe to consider only the assessment results of misalignment of welds and welding angle deformation,but the assessment results are too conservative,and the fatigue strength evaluation results of the two-plate butt joints with different welding processes are more accurate based on the calculation formula of the stress amplification factor proposed in this paper.