Study On Fatigue Performances Of Overlap Non-penetrating Laser Welded Stainless Steel Carbody Plates

ABSTRACT:301L series of cold-rolled stainless steel plate is the main material in manufacturing railway body, it’s more suitable for low heat input welding way due to its cold hardening characteristics.Currently spot welding is the main welding way for the railway body, but poor air-tightness structure is not conducive to the use of bullet train. The emergence of laser welding can not only meet the requirements of plate welding of low heat input, but also it is able to resolve spot welding defects of air tightness poor, so it has wider application.In this paper, the study is based on non-penetrating laser welding lap joints to carry static tensile and fatigue test, which is made for three series of301L strength of cold-rolled sheet.The static tensile mainly provides a reference for fatigue testing loads, the paper focuses on the study of the fatigue properties of laser welded joints.It includes fatigue life analysis of trials, researching the relationship between fatigue load and fatigue life of different combinations lap specimens, and comparative study of the optimum fatigue properties of welded sheet metal category, the determination of the S-N curve. It compares each lap weld fatigue performance from multiple perspectives, analyzes fatigue fracture mode and fatigue fracture morphology. The fatigue crack initiation region, the expansion path and other aspects of specimens combine with exhibited fatigue performance to study and compare different plate combinations. Using finite element simulation of stress concentration specimen, affecting of the stress distribution on the penetration depth to predict the location of fatigue failure, and the affecting of weld joint geometry parameters on fatigue performance.Testing and researching showed that:For three series of301L, the higher the intensity of the plate used for the test series in three301L cold rolled sheet is, the better welded joint fatigue performance is, and the load of beyond fatigue life is relatively high; fatigue life of welded specimens mainly consists of initiation life and crack propagation life. Fracture analysis showed that, for the high life welded specimens, crack initiation life account for more than90%, sheet strength has a greater impact on the fatigue properties of the weld; specimen fracture locations are near the weld edge of the outer panel, special structural position leads to severe stress concentration. Finite element analysis, which has tensile stress, which is easy to crack initiation.Welding penetration has small affect for maximum stress, but it has a great impact on the actual specimen fatigue life.Generally it has a recommended penetration rate between20%and40%.