Papers by Keyword: Deformation Mechanism

Abstract: Titanium alloys typically exhibit a limited ductility (typically 20%) and little strain-hardening. An alloy design with new concept was conducted aiming at improving both ductility and strain hardening while keeping the mechanical resistance at an excellent level. An experimental validation was illustrated with the Ti-12(wt.%)Mo alloy, exhibiting true stress - true strain values at necking, of about 1000MPa and 0.38, respectively, with a large strain hardening rate close to the theoretical limit. In order to clarify the origin of this outstanding combination of mechanical properties, detailed microstructural investigation and phase evolution analysis were conducted by means of in-situ synchrotron XRD, in-situ light microscopy, EBSD mapping and TEM microstructural analysis. In the deformed material, combined Twinning Induced Plasticity (TWIP) and Transformation Induced Plasticity (TRIP) effects are observed. Primary strain/stress induced phase transformations (β->ω and β->α’’) and primary mechanical twinning ({332}<113> and {112}<111>) are simultaneously activated in the β matrix. Secondary martensitic phase transformation and secondary mechanical twinning are then triggered in the twinned β zones. The {332}<113> twinning and the subsequent secondary mechanisms are shown to be dominant at the early stage deformation process. The evolution of the deformation microstructure results in a high strain hardening rate (~2GPa) bringing both a high tensile strength and a large uniform elongation.

Abstract: The creep behavior of a Re-free single crystal Ni-base superalloy at high temperature has been investigated by means of creep property measurement and microstructure observation. The experimental results show that the creep life of the alloy under the testing condition of 1040 oC/137 MPa was measured to be 556h. In the primary stage of creep, the deformation mechanism of the alloy is dislocations slipping within the γ matrix, and the γ′ phase in the alloy is transformed into the rafted structure along the direction vertical to the stress axis. In the latter stage of creep, the alternate activation of the main/secondary slipping dislocations may twist the rafted γ′ phase to promote the initiation and propagation of the cracks along the interfaces of γ′/γ phases up to the creep fracture. And the various configurations of the rafted γ′ phase appeared in the different regions of the sample, thereinto, the coarsening and twisting of the rafted γ′ phase in the regions near the fracture may be attributed to the bigger plastic deformation.

Abstract: The deformation and failure problems in soft rock supporting cannot be effectively controlled with conventional methods. This paper put forward the coupling support technologies by the use of large deformation constant-resistance bolt, large deformation constant-resistance cable and bottom-grouting pipes, with the analysis of deformation and failure reseasons, combing with verifications in field-test project at B103W01 working face, State Grid Energy abundance Coal Limited Shajihai Coal Mine. It also provides the reference for the tunnels supporting under similar conditions.

Abstract: Steel casing damage in oil wells is the primary hazards of oil production in China. There are two main reasons for the steel casing damage, one is the displacement loads on the external interface which primary come from rock creep, and another reason is temperature load on the internal surface which comes from steam injection. In this article, rock creep under fluid-solid interaction is calculated, and the displacement loads on external interface of steel casing is worked out. Then, steel casing deformation and crack propagation with temperature load is investigated. Underground rocks can be treated as porous media and rock creep is controlled by fluid-solid interaction for porous media. The method of fluid-solid interaction for finite element analysis is the calculation of two-way fluid-solid coupling for porous media; it means fully coupling between the solid and fluid solution variables. This method is analyzed and the displacement load is worked out as an example application. Finite element model is constructed; deformation and crack propagation of steel casing under multiple actions of outer loads and inner temperature load are calculated. Finally, fracture mechanism of steel casing in oil wells is analyzed, and some advice is proposed.

Abstract: The aim of the present study was to investigate the role of deformation temperature on the active deformation mechanisms in a 0.6C-18Mn-1.5Al (wt%) TWIP steel. The tensile testing was performed at different temperatures, ranging from ambient to 400°C at a constant strain rate of 10^-3 s^-1. The microstructure characterization was carried out using a scanning electron microscopy. The deformation temperature revealed a significant effect on the active deformation mechanisms (i.e. slip versus twinning), resulting in different microstructure evolution and mechanical properties. At the room temperature, the mechanical twinning was the dominant deformation mechanism, enhancing both the strength and ductility. Dynamic strain aging (DSA) effect was observed at different deformation temperatures, though it was more pronounced at higher temperatures. The volume fraction of deformation twins significantly reduced with an increase in the deformation temperature, deteriorating the mechanical behavior. There was a transition temperature (~300°C), above which the mechanical twinning was hardly observed in the microstructure even at fracture, resulting in low ductility and strength. The current observation can be explained through the change in the stacking fault energy with the deformation temperature.

Abstract: The precision turning experiments of aluminium composites reinforced with SiC whisker reinforcements were done by polycrystalloid diamond (PCD) tools. The measure analysis of the machined surface was carried out with Atom Force Microscope (AFM) and Scan Electronic Microscope (SEM). The roughness values of the machined surface were measured by Talysurf-6. The results show that the orientation of reinforcements in the machined surface will directly affect the deformation mechanism of SiC whiskers, microstructures of the machined surface, and to determine the quality of the machined surface. In the five types from A to E of SiC whisker orientation, the orientation of case A easily makes to produce SiC whisker deformation by cutting off directly, and to result in the best machined surface. However, for the orientation of case E, it easily makes to induce SiC whisker deformation by pulling out or pressing into aluminium matrix, and to produce the worst machined surface.

Abstract: For the soft rock roadwaysupporting problems, using the conventional methods cannot effectively controlthe deformation and failure. This paper took B103W01 transport gateway projectin Shajihai coal mine as example and analyzed its deformation failure reasonand deformation mechanism and determined the specific measures of transformingcompound mechanism of deformation mechanics into a single type. In the end, weput forward coupling support technology of constant resistance and largedeformation bolt + hollow grouting anchor + corner grouting steel pipe, whichhad been applied to engineering practice. The monitoring results showed thatthe supporting effect was good. So it can be used for reference for the similarconditions of roadway supporting.

Abstract: The pressure control of soft-rock and roadway support has been one of the challenges of underground mines. Soft-rock support is very difficult in many places in China and is becoming a kind of main influencing factors in the development and economic of mining community. Numerical simulation research on the deformation mechanism of soft-rock tunnel contributes to the development of soft-rock support theory. The numerical calculation model of shallow buried soft-rock is based on Hongya coalmine; ANSYS is used to analysis the deformation law inward to find out how to control the soft-rock deformation. Hence we can know the main influence in the shallow soft-rock tunnel stability. The results are of great importance to the mines that have similar geological conditions.

Abstract: B1 coal seam located at -550m level in Liangbei Coal Mine is a typical "three-soft" seam. The coal roadway with a depth of 610-750m lies under the critical softening depth of the roadway, and its support difficulty coefficient is 1.5-2.0. The coal has poor air permeability, high gas content and high gas pressure, so danger degree of the gas outburst is relatively strong. The coal seam was destroyed in a disastrous state by more than 100 boreholes for gas outburst prevention during the excavation. This results in the difficulty in the roadway support. Engineering geological characteristics of the coal roadway at 11 mining area are introduced. Based on the engineering geo-mechanics method, the reasons of deformation and failure of the coal roadway are analyzed. In view of problems in excavation and support, as well as the type of the coal roadway deformation mechanism, the borehole parameters are optimized for the gas outburst prevention, and bolt-net-cable coupling support with high convex steel-belt is used to control the coal roadway stability at 11 mining area. Practice shows that the effect is fine.

Abstract: TG6 alloy is a new titanium alloy which has been designed to reach the service temperature of 600°C. The microstructural evolutions of TG6 alloy under different thermal mechanical treatments were studied. It was found that lamellar microstructures with basketweave α lamella are obtained for TG6 alloy forged in β field. The evolution mechanism is transformed from dynamic recrystallization to dynamic recovery and the thickness of α lamella increases with increasing forging temperature. The aspect ratio of α lamella decreases firstly and then increases with increasing deformation degree. Grain boundary α lath appears when the deformation degree is less than 40%. The thermal mechanical treatments, including deformation in β field firstly and then deformation in α+β field result in the transformations of the microstructures drastically. The deformation degree in α+β field decides the final microstructure. The deformation degree of 20% in α+β field results in partial globular α phase.