Fatigue Life Research For Welded Frame Based On Notch Stress Method

The fatigue reliability of mechanical structure is the key factor to determine the quality of the product,how to make use of structural fatigue design and analysis method is an effective way to guarantee fatigue reliability of mechanical structure.traditional nominal stress method and structural stress method(hotspot stress method)are widely adopted in domestic and foreign countries.The nominal stress neglects structural influences of weld details.It has a difficulty to confirm parameters of nominal stress and match with the typical welded joints in standards.The structural stress method considers the size of welding line details,but the notch of weld toe and weld root have the strong mesh-sensitivity,which is easy to result in singularity of local stress.In order to overcome the defect of traditional anti-fatigue design method,a more accurate and reliable notch stress method is introduced to study fatigue life of vehicle welding structure.1?References welded joint fatigue test data,establish welding structure fatigue life curve,and compare parameters of the fatigue life curve to the data of welding structure design specification,analysis the differences and the reasons.2?Compare the difference between the formula and the numerical method,calculate the stress concentration coefficients of two samples.And discussed the influence of plate thickness and weld angle on stress concentration.and calculate the stress concentration of the butt joint was calculated as 1.61;The stress concentration factor at the corner welding toe is 2.71,and the stress concentration factor at the welding root is 4.42.3?The research object is the bogie of a moving vehicle,the nominal stress model and the notch stress model of the bogie are established.By comparing the stress states of the two models,the advantages and disadvantages of the two models are discussed;According to the life test procedure of graded loading in EN13749 standard and S-N curve,analysis the key points fatigue cumulative damage.4?The research object is to a movable tube joint,analysis the influence of different welding Angle,welding throat depth and grinding radius on cumulative damage,give the optimum grinding radius of the welded joint;compare the test S-N curve and the IIW standard S-N curve,analysis the effects of two curves on cumulative damage.