Materials Science Forum Vols. 575-578

Abstract: In order to understand the solidification behavior in the semi-continuous casting process of 7B50 aluminum alloy, a thermo-mechanical model for the analysis of 7B50 aluminum alloy solidification process is presented, this model considering liquid-solid phase-change effects for the solidification alloy. The thermal contact conductance between the mould wall and the ingot, the convective heat transfer coefficient are taken into account in the model. The distribution of temperature and stress in the process of semi-continuous casting of 7B50aluminum alloy are analyzed in three-dimensional finite element methods based on the above models. The variation of casting speed to influence the temperature and stress of the ingot in the process of semi-continuous casting is studied.

Abstract: In order to meet the demand of steelmakers, series of experimental facilities such as thermo-mechanical simulator, pilot hot rolling mills, controlled cooling system, pilot cold rolling mills, simulator for continuous annealing of strips, and hot-dip galvanizing simulator have been developed and applied by the RAL. These instruments can be used to simulate different processing technologies of steel forming which include continuous casting, hot rolling, controlled cooling, cold rolling, annealing and surface treatment(such as coating), etc. They provide unique research means for the R&D activities of China’s iron and steel industries. The characteristics, experimental functions, performance parameters and application of these facilities are introduced in the paper.

Abstract: The fracture development during wire drawing operation is an important phenomenon governing the productivity as well as the mechanical properties of the drawn wire. The wire drawing processes was investigated in present paper in two separate levels - using the 2-dimensional rigid-plastic finite element method (macro-level) and modelling the microstructure changes (micro-level) by the Representative Volume Elements (RVEs). To predict fracture initiation the phenomenological theory of fracture is used. The influence of initial cementite lamellas orientation on triaxity factor and localization of deformation in micro-level is investigated. Obtained results are helpful for a fundamental understanding of pearlitic deformation during development of high strength steel wires for tire cord applications.

Abstract: The warm compaction process is simulated by the finite element analysis software which is MSC/MARC. The thermal mechanically coupled analysis method is applied based on the updated Lagrangian Method to simulate powder warm compaction process under different frictional condition and different strain rate. The influence of different friction condition and strain rate is researched on the density and the mechanics behavior of powder green. The results indicate that for cylindrical powder metallurgic products, with the increasing of pressing velocity (namely strain rate), work hardening of powder is gradually evident, and leads to larger distribution grads of density and equivalent stress of green. The improvement of friction condition is propitious to reduce the disadvantage of work hardening and improve the uniformity of distribution of density.

Abstract: The paper reveals information about crack behavior during hot rolling of heavy-gauge products. FEM-based mathematical modeling has been used to investigate the impact of crack shape and rolling parameters on the distribution of the principal tensile stress and the Cockroft-Latham fracture criterion value and on the crack closing capacity. The results clearly show that the crack shape has the most powerful influence on the observed quantities followed by the rolling geometry factors. To find a critical value of the LCK for a specific steel grade and an actual rolling process, a laboratory experiment has been conducted, in which problems related to propagation of initial cracks were detected. It consisted in rolling of wedge-shaped specimens with a notch, which was introduced for the purpose of raising the probability of crack occurrence. In order to find the Critical LCK value in the area of the notch, an additional computer simulation was performed. Results of these experiments led to the conclusion that the steel possesses excellent formability. The Critical LCK values were up to 300 MPa, which is, essentially, an order higher than in actual rolling. As the critical value of LCK depends, among others, on the metallurgical characteristics of the metal, the key to the issue is in the steel microstructure. The findings brought the conclusion that in this specific case the rolling itself affects the crack propagation to a small extent only. The heating process poses a much greater challenge, as it is the likely stage involving the steel overheating.

Abstract: Dyes are colored organic compounds that are used to pigment fiber or other materials. Dyes are mainly calssified into natural and synthetic dyes in terms of the origin. Natural dyes include animal dyes, plant dyes and mineral dyes with such defects as incomplete chromatogram, inconvenient use and color fading, and thus have been gradually eliminated. In 1856, the 18-year-old young British scientist Perkin successfully invented the world's first synthetic dyes. He built his own factory and industrialized synthetic dye production. Over 100 years since then, dye industry has undergone rapid development, and by 2001 synthetic dyes already have been up to nearly 10,000 varieties. In 2004, the output of total dyes in the world has reached 900,000 tons. Synthetic dyes are used comprehensively, not only to dye synthetic fibers, but also natural fibesr, fur, leather and man-made fibers.

Abstract: Hot ring rolling (HRR) is a 3D unsteady-state and coupled thermo-mechanical process, the metal undergoes complicated unequal deformation and microstructure evolution. In this paper a 3D rigid-plastic and coupled thermo-mechanical FEM model for hot ring rolling was developed based on DEFORM3D platform, taking dynamic recrystallization (DRX) volume fraction, DRX grain size, recystallization volume fraction and average grain size as objects, the mechanism of material microstructure evolution and distributions in HRR process are thoroughly studied. The results show that: with the HRR progressing, the DRX volume fraction, volume fraction, DRX grain size and average grain size have the similar distributing characteristic, and the distribution zones expand from a small local area into the whole ring strip, then diffuse to the mid-layer of ring with small deformation, their distributions become more uniform. Meanwhile with increase of deformation, the values of the DRX volume fraction and recrystallization volume fraction augment, i.e. the degree of recystallization increases. The DRX grain size also augments due to local high temperature, while the average grain size decreases. In general during HRR process the distributions of DRX volume fraction, recrystallization volume fraction, DRX grain size, and average grain size are ununiform due to unequal deforming in HRR process.

Abstract: Railcar wheels and axles belong to the most critical components in railway vehicles. The service conditions of railway vehicles have been more severe in recent years due to speed-up. Therefore, a more precise evaluation of railcar wheel life and safety has been requested. Wheel/rail contact fatigue and thermal cracks due to braking are two major mechanisms of the railcar wheel failure. One of the main sources influencing on the contact zone failure is residual stress. The residual stress in wheels formed during heat treatment in manufacturing changes in the process of braking. Thus the fatigue life of railcar wheels should be estimated by considering both thermal stress and rolling contact. Also, the effect of residual stress variation due to manufacturing process and braking process should be included in simulating contact fatigue behavior. In this paper, an evaluation procedure for the contact fatigue life of railcar wheels considering the effects of residual stresses due to heat treatment, braking and repeated contact load is proposed. And the cyclic stressstrain history for fatigue analysis is simulated by finite element analysis for the moving contact load.

Abstract: Based on the calculation formulas of heat treatment temperature field of the narrow strip spot of laser beam passing a scanning rotating mirror, the effect of scanning frequency on temperature field was analyzed in this study, and the math model of the temperature field with scanning frequency was derived applying the superposing principle of the temperature field. The value simulation and figures description were given. The relationship between scanning frequency and temperature distribution was studied, and the best extent of frequency was given for carbon steel laser quenching with laser rotating mirror. The value simulation shows that the higher the scanning frequency is, the more evenly distributed the temperature field gets. At a certain laser power and a certain length of laser scanning line spot, for non-melting laser heat treatment under the spot, a maximum thickness of the high- temperature layer can be get at some certain scanning frequency range which depends on thermal diffusion coefficient of the material.

Abstract: An approach of numerical modeling and simulation algorithm is presented to predict dynamic behaviors of one kind of antenna radomes materials efficiently. Considering the dynamic behaviors in the lateral and interior of the antenna radomes materials, the dynamic simulation equations of the antenna radomes materials is established based on a dynamic boundary element method (DBEM) by using the domain reducing to decrease computational scale and costs of the equations greatly, and the dynamic behaviors of the antenna radomes materials can be gotten effectively. Numerical simulation calculating and experiments show that the presented method not only saves computational efforts, raises analytical efficiency and simulation accuracy but also can provide the theoretical bases for avoiding the weak pose of the antenna radomes materials. It has very important reference value for improving theoretical calculation and design level of the antenna radomes materials.