The Measuring Of Spot Welding Residual Stress Of Ultra-high Strength Steel And Numerical Analysis

B1500H ultra-high strength steel has good punching performance and goodcorrosion resistance as well as high strength. It has been widely applied to theautomotive industry, and become an important method to automobiles of light quality.In automobile manufacturing, the resistance spot welding is the most main weldingmethod. The advantage of good welding process is more conducive to automatedproduction. Welding residual stress will appear with the completion of the spotwelding process. The existence of the welding residual stress will affect theperformance of component, reduce its fatigue life, therefore, the study of reducewelding residual stress has become more and more important.In this study, there are mainly two parts of resistance spot welding residual stresstesting and numerical analysis.The research contents of the part of testing: firstly, finished the resistance spotwelding experiments of B1500H steel sheet material under the different weldingprocess. Secondly, measured the surface residual stress of welding components byX-ray diffraction method, the measurement area including nugget, heat affected zoneand the base metal zone. Analyzed the measuring result and find that residual stresshas a symmetric distribution centered on nugget, the maximum value appears in heataffected zone and increase with the increasing of electrode diameter and current.Thirdly, tested the elasticity modulus and poisson ratio of spot welding componentsthe measurement area including nugget, heat affected zone and the base metal zone.At last, finished the overload stretch by universal testing machine on weldedcomponents, then unloaded and analyzed the reduction effect of residual stress by theX-ray diffraction method and find that the stress in nugget and heat affected zone havereleased under5kN stretch force.The research contents of the part of numerical analysis: firstly, resistance spotwelding model is established by the finite element software SYSWELD based on thethermal elastic-plastic theory. Get the temperature field, residual stress field andforecast the diameter of nugget. Secondly, change the welding process includingwelding current, welding time, electrode pressure and studying the influences tonugget temperature, nugget diameter and residual stress field. The result of numericalanalysis show that the nugget diameter increased with the increase of welding currentand welding time, the residual stress reduced with the increase of electrode pressure.Thirdly, import the result of spot welding numerical simulation to finite elementsoftware PATRAN&NASTRAN, and combine with the mechanics propertiesparameters by ultrasonic method. Via the simulation of the spot welding components overload stretching and unloading. The results show that residual stress obviouslyreduced and the reduce effect of nugget is more obviously than the face of weldingstructure.