Papers by Keyword: Deformation Mechanism

Abstract: By means of creep properties measurement and microstructure observation, an investigation was carried out to study the creep behaviors of the as-cast TiAl-Nb alloy at temperature near 910 oC. Results showed that the microstructure of as-cast TiAl-Nb alloy consisted of γ/α₂ phases with the lamellar feature, and the boundaries with irregular serrated configuration consisted of single γ phase, and located in between the lamellar γ/α₂ phases with different orientations. The as-cast TiAl-Nb alloy displayed a better creep resistance at high temperature and longer creep life. Compared to α₂ -Ti₃Al phase, the γ phase possessed a weaker strength, therefore, the crack was easily initiated along the boundaries at about 45° angles relative to the stress axis, and propagated along the boundaries parallel to the orientation of lamellar γ/α₂ phases up to the occurrence of creep fracture. Thereinto, the tearing edges formed on the surface of the fracture being inclined with the lamellar γ/α₂ phases are attributed to the α₂-Ti₃Al phase with better strength hindering the crack propagation during creep.

Abstract: Fe-Mn-C alloys with different carbon content were investigated. It was found that carbon element effected the SFE of the Fe-Mn-C alloys seriously, SFE increases with increase of carbon concentration. Fe-Mn-C alloys' deformation mechanisms, with SFE increase from 9.04 mJ.m^-2 to 39.99 mJ.m^-2, turn transformation-induced plasticity (TRIP) effect into twinning-induced plasticity (TWIP) effect with carbon concentration increase from 0.16% to 0.98%.

Abstract: Dynamic mechanical properties and microstructures of pure iron and Fe-30Mn-3Si-4Al TWIP (TWinning Induced Plasticity) steel were conducted by SHPB (Split-Hopkinson Pressure Bar), OM (Optical Microscopy) and TEM (Transmission Electron Microscope), at the strain rate ranging from 10² to 10⁵ s^-1 and at room temperature. The effect of high strain rate on the mechanical responses of pure iron and Fe-30Mn-3Si-4Al TWIP steel belonging to BCC (Body Centered Cubic) and FCC (Face Centered Cubic) structures respectively was evaluated. The comparison of deformation mechanism was analyzed between them and it concluded that dislocation gliding is a major deformation mechanism in pure iron with BCC structure and deformation twinning plays a significant role in Fe-30Mn-3Si-4Al TWIP steel with FCC structure.

Abstract: With the development of transportation construction, soft rock tunnel with high geostress construction has become a key problem to overcome of traffic engineering construction. In order to explore the deformation mechanism and control technology of soft rock tunnel with high geostress, Xiakou tunnel engineering as an example, the geological characteristics and deformation characteristics of the tunnel were analyzed, to obtain the deformation mechanism of soft rock tunnels with high geostress, and to develop deformation control technology, the results provide a basis and reference for the domestic and foreign the similar engineering construction.

Abstract: Semi-solid billet of 9Cr18 martensitic stainless steel with globular grains was made by a wavelike sloping plate experimental device, and hot compression tests were carried out in the semi-solid state of 9Cr18 semi-solid billet on Gleeble-1500 thermal simulation testing machine at the temperatures of 1250°C ~1300°C and the strain rates of 0.1 s^-1 ~5.0 s^-1 to investigate the effects of thixoforming parameters on its deformation characteristics and mechanism. According to the true stress-strain curves obtained from the test, the influence of deformation temperature and strain rate on 9Cr18 semi-solid billet deformation resistance was investigated, and the deformation resistance model of specimen with coexistence of solid and liquid phases was established. In this paper, it was found that deformation mechanism changed because of different deformation temperature and strain rate. Dynamic recrystallization occured at 1250°C in different phases separately. So that big fine recrystallized grains were achieved at the soft primary austenite region while small recrystallized grains were achieved at the hard solidified liquid region. The melted metal would be extruded from the centre of the specimen to the free surface completely when the temperature was higher than 1275°C. And then specimen became FGM (functionally graded materials), with phases and properties graded distribution perpendicular to the stress direction. When thixoforming temperature reached 1300 °C, martensitic transformation occurred after rapid cooling. The mathematics models of the relation between stress and temperatures, fraction of solid, deformation rates and deformation degree of 9Cr18 semi-solid billet were regressed and established based on the dates attained from the compression deformation experiments. The R value was 0.991, and the RMSE value was 3.57.

Abstract: To study the relation between surface morphology and deformation mechanism of the target material under the shock, a flexible boundary loading, in laser shock peening (LSP), the macroscopic and microscopic surface morphology of a single crystal copper treated by LSP was investigated. The optical profilometer shows a 200-μm-deep pit forms on the shocked surface under LSP. The optical microscopy shows a set of parallel slip bands appear at the center of the shocked region and many vertical cross slip bands appear at the edge of shocked region. This indicates a large plastic deformation occurs by means of slip for the single crystal copper under LSP and the distributing features of slip bands correspond to the spatial distribution of the shock pressure. The results confirm that the surface morphology of materials under LSP can reflect the deformation mechanism and it can be a new method of studying the deformation mechanism of materials under LSP.

Abstract: Single point incremental forming (SPIF) process is the latest sheet metal forming technique, which developed in the around 1990, this process could generates a local strain on a sheet metal by mean of small rotation forming tool travel follow CNC toolpath on sheet metal blank to form a shell part. The incredible elongating without failure occurs is the main advantage of this process. This paper attempt to explain the deformation mechanism of steel sheet that formed by SPIF in the metallurgical views. The different degree of deformation were investigated by optical microscope, the grain size deformation was used as a data for math modeling of the deformation mechanism.

Abstract: The stress of slope is in dynamic changes from open-pit to underground of the mining excavation . In this article, based on the relationship of space corresponding through the two mining methods, and two types of mining influence dominated overprint and containing characteristics, it can find out its regularity according to the numerical simulation, and also can reveal the induced with mutual interference between two excavation system mechanism, deformation of foundation and its numerical size out of dangerous area from the mining effect of interaction and mutual superposition characteristics; On this basis, it also analyzes its influence on the stability of the slope characteristics and deformation law, and puts forward to the control methods which provide the decisions basis for the mining safety production.

Abstract: Fe-Mn-C alloys with different carbon content were developed as automobile sheet. Their mechanical properties were studies after hot rolled-cold rolled-different temperature annealed. It was found that carbon element effected mechanical behavior of Fe-Mn-C system alloys seriously. With carbon element increasing its deformation mechanisms turned transformation-induced plasticity (TRIP) effect into twinning-induced plasticity (TWIP) effect. Then the Fe-Mn-C alloys with different carbon content showed different mechanical behavior and different microstructure characterization.

Abstract: Twice serious deformation occurred in the Wangxia unstable rock mass in 2010 and 2011 in Wushan country in the Three Gorges Reservoir. It formed a large dangerous factor for the local resident and channel safety. Based on the detailed investigation of the new cracks, deformation history, GPS observations, total station monitoring and crack displacement monitoring data analysis, analyzed comprehensively the deformation and reasons of the unstable rock. The researches show that the deformation type of the unstable rock mass contains gradual change and mutation, should adopt the corresponding monitoring methods and monitoring frequency in different deformation stages based on the geological survey and monitoring the key parts of the unstable rock mass. The destruction of the Wangxia unstable rock was a gradual process, controlled by 5 key cracks, which were crack T11, T12, T13, T16, and T10, consider the Wangxia unstable rock was subsided extrusion type collapse.