Deformation Stability of GH4033 Superalloy in the Hot Continuous Rolling Process Based on Dynamic Material Model and Finite Element Model

The flow stress behavior of GH4033 superalloy was determined by the hot compression tests at the temperatures of 1223-1473 K and the total strains of 0.6 with the strain rates of 0.001-30.0 s^(-1) by using cylindrical samples.The processing maps based on the dynamic material model(DMM)combined with the corresponding microstructure observations indicate the reasonable processing domain locating at the strain rates of 0.1-1.0 s^(-1) and the deformation temperature of 1273-1423 K.Meanwhile,the numerical simulation based on finite element model(FEM)described the variation of the effective strain,effective strain rate and the temperature for the core node,and unveiled the influence of the hot rolling parameters considering the initial temperature(T_(0))range of 1223-1473 K and the first-stand biting velocity(v_(0))range of 0.15-0.35 m·s^(-1).Furthermore,the deformation stability of GH4033 superalloy in the round rod hot continuous rolling(HCR)process is described and analyzed by coupling the three-dimensional(3-D)processing map,and the spatial trajectory lines were determined by the numerically simulated temperatures,the strains and the strain rates.Finally,the results show that the hot deformation stability of GH4033 can be achieved by the rolling process parameters located at T_(0)=1423 K and v_(0)=0.25 m·s^(-1).Additionally,the practical HCR processes as T_(0)=1423 K and v_(0)=0.15,0.25,0.35 m·s^(-1) were operated to verify the influence of the hot rolling parameters on the hot deformation stability by the microstructure observation of the final products.

Hot Deformation Stability of Extruded AZ61 Magnesium Alloy Using Different Instability Criteria

The hot deformation stability of extruded AZ61 magnesium alloy was investigated by means of hot com- pression tests at the temperature range of 250-400 ℃ and strain rate range of 0.001-1 s^-1. The 3D instability maps considering the effect of strain were developed to delineate the regions of unstable flow on the basis of Jonas＇s, Semiatin＇s, Prasad＇s, Murty＇ s, Gegel＇s and Alexander＇s criteria. Since non-uniform deformation occurs due to the initial microstructure inhomogeneity, the friction, etc., finite element simulations were performed to determine the position of the specimens which can mostly represent the preset deformation parameter. Detailed microstructural investigation on such position was carried out to examine the validity of the instability maps, and the results indicate that for extruded AZ61 magnesium alloy： （1） Jonas＇s and Semiatin＇s criteria conservatively predict the instability regions; （2） Gegel＇s and Alexander＇s criteria inadequately predict the instability regions; （3） Prasad＇s and Murty＇s criteria provide more effective predictions of the instability regions than Jonas＇s, Semiatin＇s, Gegel＇s and Alexander＇s criteria,

Analysis of mechanical behavior of soft rocks and stability control in deep tunnels

Due to the weakness in mechanical properties of chlorite schist and the high in situ stress in Jinping II hydropower station, the rock mass surrounding the diversion tunnels located in chlorite schist was observed with extremely large deformations. This may significantly increase the risk of tunnel instability during excavation. In order to assess the stability of the diversion tunnels laboratory tests were carried out in association with the petrophysical properties, mechanical behaviors and waterlweakening properties of chlorite schist. The continuous deformation of surrounding rock mass, the destruction of the support structure and a large-scale collapse induced by the weak chlorite schist and high in situ stress were analyzed. The distributions of compressive deformation in the excavation zone with large deformations were also studied. In this regard, two reinforcement schemes for the excavation of diversion tunnel bottom section were proposed accordingly. This study could offer theoretical basis for deed tunnel construction in similar geological condition~

Deep-seated large-scale toppling failure in metamorphic rocks：a case study of the Erguxi slope in southwest China

Deep-seated large-scale toppling failure presents unique challenges in the study of natural slope deformation process in mountainous regions.An active deep-seated toppling process was identified in the Erguxi slope located in southwest China,which affected a large area and damaged critical transportation infrastructure with the volume of the deforming rock mass exceeding 24×10~6 m^3.It poses significant risks to the downstream Shiziping Hydropower Station by damming the Zagunao River.Field investigation and monitoring results indicate that the deformation of the Erguxi slope is in the advanced stage of deep-seated toppling process,with the formation of a disturbed belt but no identifiable master failure surface.It was postulated that the alternating tensile and shear strength associated with the hard/soft laminated rock strata of metasandstone and phyllite layers preclude the development of either a tensile or shear failure surface,which resulted in the continuous deformation and displacement without a catastrophic mass movement.The slope movement is in close association with the unfavorable geological conditions of the study area in addition to the construction of transportation infrastructure and the increase of the reservoir level.On the basis of the mechanism and intensity of the ongoing toppling deformation,a qualitative grading system was proposed to describe the toppling process and toevaluate the slope stability.This paper summarized the field observation and monitoring data on the toppling deformation for better characterizing its effect on the stability of the Erguxi slope.The qualitative grading system intends to provide a basis for quantitative study of large-scale deep-seated toppling process in metamorphic rocks.

Study on gob-side entry retaining in fully-mechanized longwall with top-coal caving and its application

Based on the engineering background of gob-side entry retaining in fully-mechanized longwall with top coal caving(GER-FLTC) on N2105 working face of Yuwu coal mine, by adopting the methods of theoretical analysis and numerical calculation, the control techniques of surrounding rocks in GER-FLTC working face are studied in this paper. The two main difficulties of stability of surrounding rocks at gob-side retained entry in fully-mechanized longwall working face are the stability control of top coal and control of large deformation of GER-FLTC working face. Interaction mechanical model between roofing and roadside backfilling in GER-FLTC is established and the equations for the calculation of roof-cutting resistance of roadside backfilling are derived. Results of numerical calculation show that the damage zones of top coal can be categorized into the delaminating zone of top coal above the backfilling, tensile damage zone of top coal above the retained roadway and shear damage zone of the upper rib of the solid coal. Stability control of top coal is the critical part to success of GER-FLTC. With consideration of large deformation of surrounding rocks of gob-side retained entry in fully-mechanized longwall, the support technique of‘‘roofing control and wall strengthening'' is proposed where high strength and highly prestressed anchor rods and diagonal tensile anchor cables support are used for top coal, high strength and highly prestressed yielding anchor rod support is used for solid coal and roadside prestressed load-carrying backfilling is constructed by high-water material, in order to maintain the integrity of the top coal, transfer load, high resistance yielding load-carrying of solid coal, roof-cutting of roadside backfilling and support,and to achieve GER-FLTC. Results from this study are successfully applied in engineering practice.

Dynamic deformation behavior of a face-centered cubic FeCoNiCrMn high-entropy alloy

In this study, mechanical tests were conducted oil a face-centered cubic FeCoNiCrMn high-entropy alloy, both in tension and compression, in a wide range of strain rates （10^-4-10^4 s^-1） to systematically investigate its dynamic response and underlying deformation mechanism. Materials with different grain sizes were tested to understand the effect of grain size, thus grain boundary volume, on the mechanical prop-erties. Microstructures of various samples both before and after deformation were examined using elec-tron backscatter diffraction and transmission electron microscopy. The dislocation structure as well as deformation-induced twins were analyzed and correlated with the measured mechanical properties. Plastic stability during tension of the current high-entropy alloy （HEA）, in particular, at dynamic strain rates, was discussed in lights of strain-rate sensitivity and work hardening rate. It was found that, under dynamic conditions, the strength and uniform ductility increased simultaneously as a result of the mas-sive formation of deformation twins. Specifically, an ultimate tensile strength of 734 MPa and uniform elongation of-63% are obtained at 2.3×10^3 s^-1, indicating that the alloy has great potential for energy absorption upon impact loading.

High‑Performance Stretchable Supercapacitors Based on Centrifugal Electrospinning‑Directed Hetero‑structured Graphene–Polyaniline Hierarchical Fabric

Stretchable supercapacitors(S-SCs)are of considerable interest as prospective energy-storage devices for wearable electronics and smart products.However,achieving high energy density and stable output under large deformations remains an urgent challenge.Here,we develop a high-performance S-SC based on a robust heterostructured graphene–polyaniline(G-PANI)anchored hierarchical fabric(G-PANI@pcPU).By precisely manipulating centrifugal electrospinning and PANI-induced two-step self-assembly process,the G-PANI@pcPU features an inter-linkage porous backbone,which open ions migration/intercalation pathways,high mechanical flexibility(elongation:400%),and large production area(>90 cm^(2)).The resultant G-PANI@pcPU presents ultra-large specific areal capacitance(Careal)of 5093.7 mF cm^(-2)(about 35 mg cm^(-2)mass loading of G-PANI)and redox reversibility in 1 M H_(2)SO_(4) electrolyte.Additionally,the G-PANI@pcPU fabric-based solid-state S-SCs show a high energy density of 69.2μWh cm^(-2)and capacitance of 3113.7 mF cm^(-2).More importantly,the superior stretchable stability(84.1%capacitance retentions after 5000 cycles)and foldable performance(86.7%capacitance retentions after 5000 cycles)of S-SCs are impressively achieved.Finally,the S-SCs realize potential applications of steady powering light-emitting diode(LED)lights at 100%strain,smart watch at bending deformation,toy car,and lamp.This work can offer an overwhelming foundation for designing advanced flexible electrodes toward new energy and smart wearable applications.