No abstract

Continuously welded rails are widely used in the Iran railway network, which are generally built using the flash-butt welding process. To accurately model the flash-butt welding process, thermal analysis, and prediction of the welding residual stresses, the influence of upsetting force on the total electrical resistance and a material model with consideration of the influence of temperature on the material properties are included in the numerical modeling. In this paper, numerical and experimental studies, including the finite element method, thermography, metallography, and hardness testing are performed to determine the characteristics of the welded UIC60 rail. By studying the fractured flash-butt welded UIC60 rails, it is shown that the location of the crack initiation and the rail failure in the web and heat affected zone of the welded rails was similar as compared to the maximum tensile residual stress calculated by numerical simulation. According to the numerical and experimental results, it is shown that four key parameters – such as the maximum temperature during the welding process, the total welding time, the upsetting time, and the upsetting force – control the size, microstructure, and the hardness profile of the heat affected zone which directly affects the characteristics and quality of welding.

No abstract

The external shape of a high-speed train nose is usually designed according to the aerodynamic considerations and to minimise the drag forces and noises. Crashworthiness of the nose is another aspect that is important from the passive-safety point of view. To improve the crashworthiness characteristics, usually there are not many options for changing the external shape of a high-speed train nose; therefore, a systematic study has been conducted to examine possible strategies in order to design crashworthy external and internal structures for a high-speed train nose. It is observed that the longer and slender noses show better crashworthiness characteristics. In addition, various multi-layer noses are studied, and the best internal-layer geometry is proposed. At the last step the effects of foam usage in different spaces between internal and external layers of the nose are shown.

No abstract

A boundary element method based on the Laplace transform technique is developed for transient coupled thermoelasticity problems with relaxation times in a two-dimensional finite domain. The dynamic thermoelastic model of Lord and Shulman (LS) is selected to show how mechanical and thermal energy conversion takes place in a coupled field. The Laplace transform method is applied to the time domain and the resulting equations in the transformed field are discretized using the boundary element method. The nodal dimensionless temperature and displacements in the transformed domain are inverted to obtain the actual physical quantities, using the numerical inversion of the Laplace transform method. The creation and propagation of elastic and thermoelastic waves in a finite domain and their effects on each other are investigated for the first time in this paper. Different relaxation times are chosen to show briefly the events that take place in temperature, displacement and stress fields considering the LS theory. Details of the formulation and numerical implementation are presented.

The present paper deals with the collapse simulation of aluminium alloy extruded polygonal section columns subjected to oblique loads. Oblique load conditions in numerical simulations are applied by means of impacting a declined rigid wall on the tubes with no friction in this task. The explicit finite element code LS-DYNA is used to simulate the crash behaviour of polygonal section columns that are undergoing both axial and bending collapse situations. In order to validate LS-DYNA results the collapse procedure of square columns is successfully simulated and the obtained numerical results are compared with actual available experimental data. Mean crush loads and permanent displacements corresponding to load angles have been investigated, considering columns with square, hexagonal, octagonal, decagonal, and circular cross-sections. It is shown that the octagonal cross-section has better characteristics from the point of view of vehicle crashworthiness under oblique load conditions.

Flash butt welding is commonly used in the manufacture of continuously welded rails. It is a resistance welding method, often performed in stationary plants, which consists of electrical heating and hydraulic forging of the rail ends. This method introduces a residual stress field in the foot, web and head of the rail. This investigation performs an electrothermo-mechanical analysis using finite element techniques to analyze the residual stress in two continuously welded rails. The residual stress results are compared with ASTM E837-99 standard test data.