Application of Laser Welding to Stainless Steel Light Rail Vehicle

Liu

et al. 2021

Chin. J. Mech. Eng.

Penetration and non-penetration lap laser welding is the joining method for assembling side facade panels of railway passenger cars, while their fatigue performances and the difference between them are not completely understood. In this study, the fatigue resistance and failure behavior of penetration 1.5+0.8-P and non-penetration 0.8+1.5-N laser welded lap joints prepared with 0.8 mm and 1.5 mm cold-rolled 301L plates were investigated. The weld beads showed a solidification microstructure of primary ferrite with good thermal cracking resistance, and their hardness was lower than that of the plates. The 1.5+0.8-P joint exhibited better fatigue resistance to low stress amplitudes, whereas the 0.8+1.5-N joint showed greater resistance to high stress amplitudes. The failure modes of 0.8+1.5-N and 1.5+0.8-P joints were 1.5 mm and 0.8 mm lower lap plate fracture, respectively, and the primary cracks were initiated at welding fusion lines on the lap surface. There were long plastic ribs on the penetration plate fracture, but not on the non-penetration plate fracture. The fatigue resistance stresses in the crack initiation area of the penetration and non-penetration plates calculated based on the mean fatigue limits are 408 MPa and 326 MPa, respectively, which can be used as reference stress for the fatigue design of the laser welded structures. The main reason for the difference in fatigue performance between the two laser welded joints was that the asymmetrical heating in the non-penetration plate thickness resulted in higher residual stress near the welding fusion line.

Section: Introductionmentioning

confidence: 99%

Fatigue Resistance and Failure Behavior of Penetration and Non-Penetration Laser Welded Lap Joints

Liu

et al. 2021

Chin. J. Mech. Eng.

“…Due to the different amount of strain-induced martensite transformed in the cold rolling process, the yield strength of cold-rolled plates ranges from 200 MPa to 700 MPa, which determines that the welding methods used in the vehicle manufacture are resistance spot welding and laser welding with concentrated heat input to reduce the deterioration of the mechanical properties of cold-rolled plates caused by welding heat [1][2][3][4]. The penetration and non-penetration laser welded lap joints are common joining method in rail passenger cars, and the non-penetration laser lap welding is an assembling method for side facade panels of passenger cars, which can not only improve corrosion resistances but also provide vehicle body with a weld-free appearance [5]. However, unlike penetration laser welded lap joints, the fatigue fracture of non-penetration laser welded lap joints usually occurs in the non-penetrated plate even if its nominal stress is much smaller than the penetration plate, which results in a large difference in fatigue performance between the two lap joints [6][7][8][9].…”

Section: Introductionmentioning

confidence: 99%

Fatigue resistance and failure behavior of penetration and non-penetration laser welded lap joints

Liu²,

et al. 2020

Preprint

The fatigue resistance and failure behaviour of penetration 1.5 + 0.8-P and non-penetration 0.8 + 1.5-N laser welded lap joints prepared with 0.8 mm and 1.5 mm cold-rolled 301L plates were investigated. The weld beads showed a solidification microstructure of primary ferrite with good thermal cracking resistance, and their hardness was lower than that of the plates. The 1.5 + 0.8-P joint exhibited a better resistance to high-cycle fatigue failure, while the 0.8 + 1.5-N joint showed a higher resistance to low-cycle fracture. The failure modes of 0.8 + 1.5-N and 1.5 + 0.8-P joints were 1.5 mm and 0.8 mm lower lap plate fracture, respectively, and the primary cracks were initiated at welding fusion lines on the lap surface. There were long plastic ribs on the penetration plate fracture, but not on the non-penetration plate fracture. The fatigue resistance stress of the penetration and non-penetration plates in the crack initiation areas calculated based on the mean fatigue limits is 408 MPa and 326 MPa, respectively. The main reason for the difference in fatigue performance between the two laser welded joints was that the asymmetrical heating in the non-penetration plate thickness resulted in higher residual stress near the welding fusion line.

“…Light weight railway passenger cars made of cold-rolled 301LN austenitic stainless steel have been widely used in subways and intercity express trains [1][2][3][4] . Non-penetrating laser lap welding is an assembling method for the side facade panels of passenger cars, which can provide vehicle bodies with a weld-free appearance and improve corrosion resistances 5,6 .…”

Section: Introductionmentioning

confidence: 99%

The effect of angular distortion on the fatigue behavior of non-penetrating laser welded lap specimens of 301LN stainless steel

Liu²,

Li³

et al. 2020

Preprint

In this work, the fatigue behaviors of non-penetrating laser welded lap specimens of cold-rolled 301LN austenitic stainless steel were investigated based on experiments and numerical analyses. The experiments showed the unequal-thickness specimens failed in the thicker bottom sheet under low fatigue loads, even though the mean stress in the thinner top sheet was higher, when the applied loads were high enough, the failure location changed from the bottom sheet to the top sheet. This phenomenon could be successfully explained through traction stress analysis considering the effect of angular distortion. However, the equivalent traction stress representation of fatigue data is below the ASME master S-N curve scatter band since the stress exceeds the yield limit of the base metal at low-cycle fatigue regime. The structural strain approach was then used to consider the effect of plastic deformation, and all fatigue data fall into ASME master E-N curve scatter band. This indicates the structural strain approach in conjunction with the master E-N curve is suitable for correlating both low-and high-cycle fatigue data of the non-penetrating laser welded lap specimens.