Chun Yuan Shi

Mechanical Properties of SUS301L Stainless Steel Welded Joints for Railway Vehicles

The tensile and the fatigue tests of three different rolling states of SUS301L stainless steel welded joints were investigated, and their S-N curves were obtained and analyzed. The typical fracture morphology of fatigue specimens were observed by scanning electron microscopy (SEM). The results indicate that the tensile strength and the yield strength of three kinds of SUS301L stainless steel welded joints increase with increasing of rolling degrees, while only the elongation rate decreases with the increasing of rolling degrees; the median fatigue limit of SUS301L-DLT、SUS301L-ST、SUS301L-MT for fatigue life 2×106 cycles are 247.5MPa, 331MPa, 266.7MPa.

Influence of Cooling Intensity on Residual Stress State of TIG Dressing Zone for T-Joint Welded Toe

Using finite element method, the residual stress distribution of the TIG dressed welded toe followed by spray treatment with different cooling intensity was calculated. And the residual stresses of welded toe were also measured by using the blind-hole method. The results indicate that with the increase of cooling intensity, the longitudinal residual stresses in welded toe are gradually transited from tensile residual stresses to compressive ones, and there is no significant change for transverse residual stresses, and the depth of compressive stress layer increases at the welded toe region.

New Application of Lap Laser Welding on Stainless Steel Railway Vehicles

Recently the problems of resistance spot welding (RSW) stainless steel railway vehicles are causing more attention for poor surface quality. Lap laser welding of stainless steel is investigated with OED(Orthogonal experimental designing ) in this study to replace RSW with the aim of to increase the aesthetics of the car body by eliminating visible indentation on the surface and the flatness of the skin reducing welding deformations. After welding tensile tests and microstructure analysis are performed. The optimization of process parameters were: laser power =2.5kW；welding speed=2.2m/min, focal position=0mm. The fusion zone is symmetrical about the axis of the laser beam and no welding cracks or porosity can be found in any of the welds. This work has great significance of improving the manufacturing level of stainless steel railway vehicles.

The Investigation of Partial Penetration Lap Laser Welding Applied on Stainless Steel Railway Vehicles

The current stainless steel railway vehicles body and structure are usually assembled by resistance spot welding process. The weak points of this process are the poor surface quality and bad airtight due to the pressure of electrodes. In this study, the partial penetration lap laser welding process was investigated to resolve the problems. The effects of the laser welding process parameters such as laser power, welding speed and focused distance to the shape of the weld seam and the shear tensile strength were discussed to find the optimal parameters. And the mechanical tests and microstructure analysis were also taken in this study. The optimal parameters are P=2.0kW，S=22mm/s，F=0mm. This work has great significance of improving the manufacturing level of stainless steel railway vehicles.

Heat Source Model of Lap Laser Welding of Stainless Steel Vehicle

Resistance spot welding (RSW) is being taken place by partial lap laser welding for the poor surface quality and bad airtight due to the pressure of electrodes. The shape of partial lap laser welding is similar to the vase. When the penetration of the joint is in a certain range, there is no welding trace on the outer surface. Laser welding temperature field numerical analysis based on Abaqus finite element analysis software is committed to obtain a suitable range of process parameters to improve production efficiency and automation by determining the joint penetration. To master the laser lap welding of stainless steel weld penetration state, the combination of three-dimensional positive cone + three-dimensional inverted cone + half-ellipsoid heat source model was established simulating stainless steel lap laser weld pool shape and forecasting the range of process parameters .

Investigation of TIG Dressing and Chilling Treatment for Improving the Fatigue Strength of Welded Joints

The negative temperature field with a certain strength is exerted on the TIG dressing zone in welding toes, which could decrease and offset the residual stress. When the temperature of TIG dressing zone is or above 450 °C, the chilling treatment could produce the stress field of biaxial compression. The chilling treatment is performed when the temperature of dressing zone is 550 °C. The fatigue strength of joints can be increased more than twice comparing with those after welding.

Numerical Analysis of Controlling Welding Deformation of the Wall Plate of Large Cylindrical Structure by Pre-Stress Method

During the welding of the wall plate of cylindrical structure, the edges of cylinder generates obvious wave-like deformation and affects subsequent assembly. In this paper, based on the numerical simulation method, welding deformation controlling by pre-stress method is studied. The effects of the pre-stress level and the welding sequence on the final deformation are discussed. The results show that the level of pre-stress can obviously control the welding deformation of the longitudinal beams, but can not control the welding deformation of transverse beams. Using the selected welding sequence: welding transverse beams firstly, exerting pre-stress, and then welding longitudinal beams, this welding sequence can reduce the wave-like deformation after welding.

Study on the Dimensional Stability of Aluminum Alloy Welded Joint under Space Thermal Cycling Conditions

Experimental and numerical investigation on the dimensional stability of aluminum alloy welded joint in thermal cycling conditions are presented. Accumulated deformation have been found during the tests. Analytical results demonstrated that the dimensional instability of the welded joint under thermal cycling is governed by the internal plastic flow rather than creep mechanisms. A finite element unit cell model is used to predict the behaviors of dimensional instability.

Fatigue Life Prediction of Stainless Steel Laser Lap Joints Based on Natural Frequency Changes

In this paper, fatigue damage and life prediction of laser lap joints were investigated based on natural frequency as the damage variable. At each fatigue stage, damage degree of laser welded specimen was monitored by the fatigue test and dynamic response tests. The results show that in the fatigue process during the increase in the number of fatigue cycles, each order natural frequency of test specimen decreased at different rate. There was almost no damage before the number of cycles reached 60% of the fatigue life, and then cracks began to initiate. When the number of cycles reaches 80% of the life, macroscopic cracks appeared and the predicted damage degree reached to 50%. Based on relation between the change rate of the natural frequency and the fatigue damage, a new fatigue life prediction model was established. The results from experimental tests were consistent with the fatigue life prediction model.

Numerical Investigation on Void Nucleation around Inclusions under Combined Mechanical and Thermal Cycling Conditions

In this paper a numerical investigation on the void nucleation behaviors under combined mechanical and thermal cycling conditions have been performed. A finite element unit cell model is conduct to calculate the local stress-strain field and describe the process of void nucleation from inclusion. Numerical results show that the thermal mismatch stress between the particles and matrix can assist the external load to cause interface debonding. Under certain mechanical and thermal cycling conditions, complicated stress and strain hystereses developed in the matrix. Both the plastic strain and plastic energy density of the interface will be accumulated during every thermal cycle. The plastic energy accumulation of the interface will first reach the debonding value and failure occurs. Based on the numerical calculation, a new energy based failure criteria is proposed to characterize the behaviors of void nucleation under combine mechanical and thermal cycling conditions.