Research On Notch Stress Field Of Thin Plate Structure And Evaluation Of N-SIF Method Under Coupling Loads

When damage happened to the ship or bridge structure,it will cause serious accidents.Based on analyzing a large number of accidents,it is found that the damage of the structure often occurs in the positions where there are incisions,such as sharp corners,grooves,and weld toes.Also,the phenomena of stress concentration appear in these positions,which affect the fatigue performance of the structure seriously.At present,the hot spot stress method is recommended by the classification societies for fatigue strength analysis on typical welded structures,but this method does not take the stress concentration into consideration caused by the nonlinear stress near the notch.The notch stress method can be used to analyze the local stress,including the notch or crack position,and it is suitable to evaluate the stress field of a typical welded joint.However,this traditional evaluation formula is complex and the calculation process is cumbersome,which is not conducive to the practical application of engineering,so it is necessary to find a simpler algorithm.In view of the above problems,researches are mainly conducted in the following aspects in this paper:（1）Based on the singular strength theory,the concept of singular strength factor is introduced,and a simple formula for calculating the stress field of V-notch is proposed,which can be applied to the calculation of bending or tensile loads.A series of finite element models with different geometric parameters are established.The stress field under tensile and bending loads is analyzed,and a simple formula for singular strength factoras₁ is obtained by fitting,which can be used for fast evaluating the stress field of the notch.Based on the finite element results,the formula proposed in this paper and the formulas in other literatures are compared and verified,and high calculation accuracy is obtained.（2）Considering the combined action of tensile load and bending load,a series of finite element models with different geometric parameters are established.The stress field of the notch under tension and bending load is analyzed.A simple formula for singular strength factoras₁ is obtained by fitting,which can be used to fast evaluate the notch stress field under complex loads.Based on the finite element results,the formula in this paper is compared and verified with the formulas in other literatures,and high calculation accuracy is obtained.（3）On the basis of the simple formula for the notch stress field of the plate specimen with the notch,the simple formula for the plate notch is applied to evaluate the notch stress field and fatigue strength of typical welded joints.The evaluation results show that,compared with the nominal stress method,the N-SIF curve obtained by the simple formula has a smaller scatter band index,which verifies the formula in this paper.