Safety Of Car Body Research Articles

Effect of welding speed on microstructure and mechanical behavior of laser welded Al-Si coated 22MnB5 steel

22MnB5 steel is a high-strength steel which can realize weight reduction and safety of car body. Al-Si coating provides excellent barrier protection for 22MnB5 steel against oxidation and decarburization during hot-stamping, but it deteriorates the weldability of the steel plate. In this paper, the effect of Al-Si coating on the weld bead formation, aluminum (Al) element distribution, the microstructure and mechanical properties of laser welded 22MnB5 steel joint was studied under various welding speed. When the welding speed was increased from 2.4 m/min to 4.8 m/min, the concavity depth of the weld surface was decreased for a given laser power of 2000 W. A flat weld bead was obtained at the welding of 4.2 m/min. During laser welding and hot stamping process, the Al element in the fusion zone (FZ) was not inhomogeneously distributed in a form of Al segregation along the fusion line. After hot stamping, the location of α-ferrite in the FZ corresponded to the Al element distribution location, and long strip α-ferrite was formed at the Al segregation. As a result, the weld was soften and the average hardness value in the FZ was only 420HV, which was 83.6% of the base metal after hot stamping (HSBM). The stress concentration at the long strip α-ferrite was the source of crack initiation and the α-ferrite in the FZ further accelerated the crack propagation along the fusion line. The tensile strength and elongation of the welded joint under the optimized parameters were 1459.65 MPa and 2.0% respectively, which were only 91.0% and 29.0% of the HSBM (1603 MPa, 6.9%).

A Study on the Safety of Carbody for Railway Vehicles

To check the structural strength of the carbody of the newly–made gondola car, load was added to the underframe of the gondola car. The objective of this study is to evaluate whether or not the underframe of a gondola car under the maximal strength is safe. A gondola car for transporting railroad freight is usually designed and made of SM490YA steel and SS400 steel. The carbody of rolling stock is a principal structure that supports major equipment of the underframe and the freight. Therefore, the strength evaluation of this structure is important. Both structural analysis and loading test were performed under the loading condition. Prior to the evaluation of structural strength, finite element method software was used for structural analyses on stress distribution in a carbody of a gondola car. The strain gauges were attached on the carbody based on FEM results. A vertical load test, compressive load test, measurement of deflection amount and a natural frequency measurement test were conducted.

Prediction of Fracture Strains for DP980 Steel Sheets Using a Modified Lou–Huh Ductile Fracture Criterion

This paper is concerned with the prediction of fracture strains for DP980 steel sheets using a modified Lou–Huh ductile fracture criterion. The usage of DP980 steel is significantly increasing in the automotive industry for weight reduction, enhancement of crashworthiness and safety of car body. The material behavior of AHSS show unpredictable and sudden fracture during sheet metal forming process. A modified Lou–Huh ductile fracture criterion is utilized to predict the formability of AHSS because the conventional FLD constructed based on necking is unable to evaluate the formability of AHSS. Fracture loci were extracted from 3D fracture envelopes by assuming the plane stress condition to evaluate equivalent plastic strain up to the point of fracture at a wide range of loading paths. Three different types of specimens such as pure shear, dog-bone and plane strain grooved specimens were used for tensile tests to construct 3D fracture envelopes of DP980. Fracture strain of each loading path was evaluated to show that there is little deviation between predicted fracture strains and experimentally acquired ones. From the comparison, it is concluded that the 3D fracture envelopes can accurately predict the onset of the fracture of DP980 steel sheets in complicated loading conditions including the pure shear condition.

Structural Strength Evaluation of a Stainless Railroad Car

This study is an experimental research on using stainless steel car body structure for urban railway vehicles. The car body used in the experiment was made of stainless steel. To evaluate the structural characteristics and safety of the stainless car body, static load test was carried out by means of "Performance Test Standard for Electrical Multiple Unit" with the reference code JIS E 7105. The structural safety of the car body was evaluated by implementing vertical load, horizontal compressive load, twist load, and 3-point support tests. Test results verified that the structural safety of a car body was very stable and safe under design load conditions.