Materials Science Forum Vols. 654-656

Abstract: In this presentation, a novel phase field grain growth model combined with a micro-elasticity effect including elastic anisotropy and inhomogeity is presented to demonstrate the effect of micro-elasticity on grain growth and texture evolution. We report on texture evolution and abnormal grain growth induced by external elastic load from the viewpoint of micro-elasticity and first demonstrate that the previous mechanism (macroscopic viewpoint) on the effect of external elastic load on grain growth does not work in strain-controlled system. In contrast to the macro-elastic descriptions, strong localization of strain energy density and inhomogeneous distribution even inside grains are observed. Moreover, elastically soft grains with a higher strain energy density grow at the expense of the elastically hard grains to reduce the total strain energy. It is observed that strong <100>//ND fiber texture was developed in poly-crystalline Cu with initial random texture by biaxial external strain while <111>//ND fiber texture evolved in biaxial external stress condition. Even, grain growth of <100>//ND textured grains is occurred as abnormal grain growth when <100>//ND textured grains are surrounded by <111>//ND fiber textured grains.

Abstract: Material-technological modelling has made great progress over recent years, thanks to the new possibilities opened up by developments in sensor technology, and especially in new methods of control, supported by innovative electronic elements and electronic circuits. One such device, developed for material-technological modelling, is the thermomechanical simulator which was established in the laboratories of the Research Centre of Forming Technologies FORTECH, in Pilsen, in the Czech Republic. Thanks to new knowledge and technical equipment the majority of technological processes or even technological chains can be modelled. The most considerable and most important innovation in the material-technological modelling process is the significant acceleration and increased precision of the modelling process. The present technology even allows modelling of highly dynamic processes, such as wire rolling including all thermodynamical effects. This paper presents the broad possibilities of the most modern material-technological modelling. The process of detecting technical and manufacturing problems during rolling and the possibilities of failure elimination are introduced in a practical example.

Abstract: Isothermal compression of near alpha Ti-5.6Al-4.8Sn-2.0Zr alloy is conducted on a Thermecmaster-Z simulator at the deformation temperatures ranging from 1173 K to 1333 K, the strain rates ranging from 0.001 s-1 to 10.0 s-1 at an interval of an order magnitude and the height reductions ranging from 50% to 70%. The primary grain size is measured at an OLYMPUS PMG3 microscope with the quantitative metallography SISC IAS V8.0 image analysis software. A multi-scale constitutive model coupling the grain size, volume fraction and dislocation density is established to represent the deformation behavior of near alpha Ti-5.6Al-4.8Sn-2.0Zr alloy in high temperature deformation, in which the flow stress is decomposed a thermal stress and an athermal stress. A Kock-Mecking model is adopted to describe the thermally activated stress, and an athermal stress model accounts for the working hardening and Hall-Petch effect. A genetic algorithm (GA)-based objective optimization technique is used for determining material constants in this study. The mean relative difference between the predicted and experimental flow stress is 5.98%, thus it can be concluded that the multi-scale constitutive model with high prediction precision can efficiently predict the deformation behavior of near alpha Ti-5.6Al-4.8Sn-2.0Zr alloy in high temperature deformation.

Abstract: In twin-roll thin strip casting, the temperature of casting roll affects the roll thermal stress, and influences the thermal deformation, the generation of roll surface cracks, the strip shape and the service life of casting roll. In this paper, the features of the casting roll materials have been analysed, the effects of the clad materials and thickness on temperature field of the casting roll have been simulated and discussed. The developed temperature model of casting roll is helpful in optimising processing parameters and the design of casting roll during twin-roll thin strip casting.

Abstract: The friction is a key factor that influences the surface quality in metal forming. To figure out the relationship between the friction and the surface roughening, a finite element model is employed in the commercial finite element software ABAQUS to simulate the surface roughness of top side of Al plate during uniaxial planar compression. With the change of friction conditions, the surface roughening varies. The average surface roughness (Ra) shows a relationship with the friction coefficient. During the surface roughening process, the grain slip takes place in the “soft orientation”, and the “hard orientations” become the barrier of the slip.

Abstract: In the cross wedge rolling process, many factors must be controlled to obtain the required plastic strain and desired tolerance values. The major factors include the wedge relative velocity, the forming angle, the spreading angle, and sectional reduction. This paper uses rigid-plastic finite element (FE) DEFORMTM 3D software to investigate the plastic deformation behavior of an aluminum alloy (A7075) workpiece as it is processed for cross wedge rolling. This study analyzes the effective strain, the effective stress, and the X-axial load distribution of the workpiece under various rolling conditions. Furthermore, using simulation software to analyze the changes to the microstructure by the rolling process, this study presents analytical results that confirm the suitability of the current finite element software for cross wedge rolling.

Abstract: the aid of commercially available software MSC.SuperForm, a 3-D finite element model has been established to simulate the rolling process of steel tubes on the stretch reducing mill (SRM) with group centralized differential drive in certain factories. A special effort was made to analyze the fluctuation of transverse wall thickness uniformity. It was found that the wall thickness of each stand was accumulated in the original pass 50°~60° along the circumferential direction, which caused the formation of the inner hexagon defects and worsen. In view of this, this paper proposes a modified roll pass design method which uses the interactive technology of CAD graph curve and MATLAB equation. By means of decreasing the lateral curvature of roll pass contour curve to enlarge the contact length between the tube and groove, also the rolling process using the new pass system were simulated and analyzed. The results indicate that the design of such polygonal roll pass can be effective in improving the inner hexagon defects.

Abstract: Heavy forgings are the essential parts of some nuclear, electrical power generation, rolling mill equipments. Based on the experimental results, one thermo-mechanica1 coupled finite element model was developed to study the effects of forging processing parameters, including the deformation degree, tool width ratio, and blank width ratio, on the axial effective strain during stretching process of heavy forgings. Results show that: (1) The effective strain around the central point rapidly increases as the deformation degree was increased. When the deformation degree is larger than 15%, there are little changes of the effective strain along the deformed block centerline. (2) The effective strain in central point increases and then decreases with the increase of tool width ratio, and the critical tool width ratio is 0.8, which is valid for most stretching processes. (3) The effective strain increases with the increase of initial blank width ratio, and the effects of blank width ratio on the effective strain in axial centerline are most obvious near the central point.

Abstract: The main aim of this work is the computer aided design of the new orbital forging process. The finite element model was developed and used in research on possibility of modification of the classical orbital forging technology based on the Marciniak press to obtain more effective process. Obtained numerical results from simulations of the new orbital process are compared with the experimental analysis, performed on the orbital press with the developed device. However, due to the novelty of the developed approach the investigation on direction of material flow during deformation is of particular interest in this work. Direction of material flow and strain path change effect due to incremental character of deformation is analyzed. Obtained results confirm good predictive capability of the FE model and are the basis for the comparison of the two processes and discussion on the effectiveness of the modified incremental forming process.

Abstract: The thin helical tube of Pd-Y alloy was mainly used to high purity hydrogen preparation. The physical phenomenon was comprehensively considered during the winding process on the thin helical tube of Pd-Y alloy. Analysis the reason of wrinkling and depression is emerged on the inner of thin helix tube during the winding process on the thin helical tube of Pd-Y alloy. Stress state was analysed on the winding process of the thin helical tube through the elastoplastic finite element method; the stress distribution law was obtained. And then, the stress state was comparative studied on the thin helical tube of Pd-Y alloy by different tension action, the control conditions of tension was presented, it was between sixty-five to seventy-five Newton. Therefore, the numerical simulation study provided theory basis for the process control of the thin helical tube’s manufacture. It was no wrinkling and depression by winding simulation test on the thin helical tube of Pd-Y alloy, satisfies requirement of using.