The hot deformation behavior of TC18 alloy at strain rates ranging from 1 × 10-4 to 1 x 10-2 s-1 and temperatures ranging from 25 to 800 ℃ was studied using a WDW-300 electronic universal testing machine. The re...The hot deformation behavior of TC18 alloy at strain rates ranging from 1 × 10-4 to 1 x 10-2 s-1 and temperatures ranging from 25 to 800 ℃ was studied using a WDW-300 electronic universal testing machine. The relationships between true flow stress decreases with stress and true strain show that the increase of temperature and increases as strain rate increases. The effect of strain rate on the flow stress becomes pronounced at higher temper- atures. At room temperature, the river pattern characteristic of brittle fracture and the dimple pattern typical of ductile fracture are found to exist in different regions of fracture surfaces of the samples. An improved constitutive rela- tionship is proposed to accurately describe the flow stress of TC18 by considering the effect of strain. And a micro- scopic model is also deduced which can link the physical mechanisms to the macroscopic experimental results. A good agreement is obtained between the predictions of the microscopic model and the results of the macroscopic experiment.展开更多
Ecological reactive powder concrete (ECO-RPC) with small sized and differentvolume fraction steel fibers was prepared by substitution of ultra-fine industrial waste powder for50% to 60% cement by weight and replacemen...Ecological reactive powder concrete (ECO-RPC) with small sized and differentvolume fraction steel fibers was prepared by substitution of ultra-fine industrial waste powder for50% to 60% cement by weight and replacement of ground fine quartz sand with natural fine aggregate.The effect of steel fiber volume fraction and curing ages on the static mechanical behaviour ofECO-RPC was studied. Using the split Hopkinson pressure bar technique, the dynamic mechanicalbehaviour of ECO-RPC was investigated under different strain rates. The results show that the staticmechanical behaviour of ECO-RPC increases with the increase of steel fiber volume fraction andcuring ages. The type of ECO-RPC with the substitution of 25% ultra-fine slag, 25% ultra-fine flyash and 10% silica fume is better than the others with compressive strength, flexural strength, andfracture energy more than 200 MPa, 60 MPa and 30 kJ/m^2, respectively. ECO-RPC has excellent strainrate stiffening effects under dynamic load. Its peak stress, peak strain and the area understrain-stress curve increase with the increase of strain rate. Its fracture pattern changes frombrittleness to toughness under high strain rates.展开更多
The work hardening and dynamic softening behaviors of Cu-6 wt pct Ag binary alloy were studied by hot compression tests under temperature range of 700-850℃ at strain rates of 0.01-10s-1.The critical conditions for th...The work hardening and dynamic softening behaviors of Cu-6 wt pct Ag binary alloy were studied by hot compression tests under temperature range of 700-850℃ at strain rates of 0.01-10s-1.The critical conditions for the onset of dynamic recrystallization （DRX） were determined based on the conventional strain hardening rate curves （dσ/dε versus σ）.The progress of DRX was analyzed by constructing a model of volume fraction of DRX based on flow curves.The strain rate sensitivity （SRS） and activation volume V were calculated.The results show that the DRX almost can happen under all deformation conditions even at high Z deformations where dynamic recovery （DRV） is the main softening mechanism.The DRX fraction curves can well predict the DRX behavior.The strain has significant effects on SRS at the strain rates of 0.01s-1 and 10s-1 which are mainly due to off-equilibrium saturation of dislocation storage and annihilation while the effects of the temperature on the SRS are based on the uniformity of microstructure distribution.The formation of ＂forest＂ of dislocation is contributed to the low activation volume V＊（about 168b3） which is independent of Z values at the initial deformation.The cross-slip due to dislocation piled up beyond the grain boundaries or obstacles is related to the low activation volume under the high Z deformation conditions at high strain （ε=0.6） while the fine DRX grains coarsed is the main reason for the high activation volume at low Z under the same strain conditions.展开更多
The creep behavior of the plasma sprayed NiCr and NiCrA1 coating/Nickel alloy 690 substrate systems at 1033 K was investigated. Results showed that there was almost no difference in the creep lives between the NiCr an...The creep behavior of the plasma sprayed NiCr and NiCrA1 coating/Nickel alloy 690 substrate systems at 1033 K was investigated. Results showed that there was almost no difference in the creep lives between the NiCr and NiCrA1 coated specimens at a given stress level, since the contents of Cr used in the NiCr and NiCrA1 powders are almost same. The relationship between the minimum creep rate and the applied stress followed the well-known Norton＇s power law, εmin=Aσ^n, with the values of A=2.66×10^-16 MPa^-n·h^-1 and n=6.48. The relation between the applied stress and time to rupture of the coated specimens can be estimated by using Larson-Miller equation. The θ projection method can be used to accurately characterize the creep behavior of the coated specimens.展开更多
A transient molecular network model is built to describe the non- linear viscoelasticity of polymers by considering the effect of entanglement loss and regeneration on the relaxation of molecular strands. It is an ext...A transient molecular network model is built to describe the non- linear viscoelasticity of polymers by considering the effect of entanglement loss and regeneration on the relaxation of molecular strands. It is an extension of previous network theories. The experimental data on three thermoplastic polymers (ABS, PVC and PA6) obtained under various loading conditions are used to test the model. Agreement between the theoretical and experimental curves shows that the suggested model can describe successfully the relaxation behavior of the thermoplastic polymers under different loading rates by using relatively few relaxation modes. Thus the mi- cromechanism responsible for strain-rate dependence of relaxation process and the origin of nonlinear viscoelasticity may be disclosed.展开更多
According to the ＂Netlike Plastic-Flow （NPF）＂ continental dynamics model, the transition of the deformation regime from brittle in shallow layers to ductile in deep layers in the lithosphere, and the controlling e...According to the ＂Netlike Plastic-Flow （NPF）＂ continental dynamics model, the transition of the deformation regime from brittle in shallow layers to ductile in deep layers in the lithosphere, and the controlling effect of NPF in the lower lithosphere result in intraplate multilayer tectonic deformation. NPF is a viscous （plastic） flow accompanied by shear strain localization, forming a plastic-flow network in the lower lithosphere. The strain rates in the seismogeulc layer can be estimated using the ＂earthquake-recurrence-interval＂ method, in which the strain rate is calculated in terms of the recurrence interval of two sequential earthquakes and the seismic probability of the second earthquake. The strains in the lower lithosphere are estimated using the ＂conjugate-angle＂ method, which takes the relationship between the conjugate angles and the compressive strains of the network, and calculates the characteristic strain rates in this layer from the strains and the durations of deformation inferred. The contour map of characteristic maximum principal compressive strain rates in the lower lithosphere in central-eastern Asia given in the paper shows strain rates with magnitudes on the order of 10^-15 - 10^-14/s in this region. The strain rates within the plastic-flow belts, which control seismic activities in the seismogeulc layer, are greater than the characteristic strain rates of the network and, in addition, the strain rates and seismic activities in the seismogeulc layer are also influenced by other factors, including the directive action of driving boundary along the upper crust, the effects of plastic-flow waves and the existence of the transitional weak layer distributed discontinuously between the upper and lower layers. The comparison between the strain rates in the seismogeulc layer and the characteristic strain rates in the lower lithosphere for 11 potential hypocenter areas in the region from the Qinghai-Xizang （Tibet） plateau to the North China plain indicates that, except for 展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.91016013 and 11221202)the Opening Research Fund of State Key Laboratory of Porous Metal Materials(No.PMM-SKL-1-2012)the Project of State Key Laboratory of Explosion Science and Technology(No.SKLEST-13-07)
文摘The hot deformation behavior of TC18 alloy at strain rates ranging from 1 × 10-4 to 1 x 10-2 s-1 and temperatures ranging from 25 to 800 ℃ was studied using a WDW-300 electronic universal testing machine. The relationships between true flow stress decreases with stress and true strain show that the increase of temperature and increases as strain rate increases. The effect of strain rate on the flow stress becomes pronounced at higher temper- atures. At room temperature, the river pattern characteristic of brittle fracture and the dimple pattern typical of ductile fracture are found to exist in different regions of fracture surfaces of the samples. An improved constitutive rela- tionship is proposed to accurately describe the flow stress of TC18 by considering the effect of strain. And a micro- scopic model is also deduced which can link the physical mechanisms to the macroscopic experimental results. A good agreement is obtained between the predictions of the microscopic model and the results of the macroscopic experiment.
文摘Ecological reactive powder concrete (ECO-RPC) with small sized and differentvolume fraction steel fibers was prepared by substitution of ultra-fine industrial waste powder for50% to 60% cement by weight and replacement of ground fine quartz sand with natural fine aggregate.The effect of steel fiber volume fraction and curing ages on the static mechanical behaviour ofECO-RPC was studied. Using the split Hopkinson pressure bar technique, the dynamic mechanicalbehaviour of ECO-RPC was investigated under different strain rates. The results show that the staticmechanical behaviour of ECO-RPC increases with the increase of steel fiber volume fraction andcuring ages. The type of ECO-RPC with the substitution of 25% ultra-fine slag, 25% ultra-fine flyash and 10% silica fume is better than the others with compressive strength, flexural strength, andfracture energy more than 200 MPa, 60 MPa and 30 kJ/m^2, respectively. ECO-RPC has excellent strainrate stiffening effects under dynamic load. Its peak stress, peak strain and the area understrain-stress curve increase with the increase of strain rate. Its fracture pattern changes frombrittleness to toughness under high strain rates.
基金supported by the Chongqing Natural Science Foundation(No.CSTC2009BA4065)
文摘The work hardening and dynamic softening behaviors of Cu-6 wt pct Ag binary alloy were studied by hot compression tests under temperature range of 700-850℃ at strain rates of 0.01-10s-1.The critical conditions for the onset of dynamic recrystallization （DRX） were determined based on the conventional strain hardening rate curves （dσ/dε versus σ）.The progress of DRX was analyzed by constructing a model of volume fraction of DRX based on flow curves.The strain rate sensitivity （SRS） and activation volume V were calculated.The results show that the DRX almost can happen under all deformation conditions even at high Z deformations where dynamic recovery （DRV） is the main softening mechanism.The DRX fraction curves can well predict the DRX behavior.The strain has significant effects on SRS at the strain rates of 0.01s-1 and 10s-1 which are mainly due to off-equilibrium saturation of dislocation storage and annihilation while the effects of the temperature on the SRS are based on the uniformity of microstructure distribution.The formation of ＂forest＂ of dislocation is contributed to the low activation volume V＊（about 168b3） which is independent of Z values at the initial deformation.The cross-slip due to dislocation piled up beyond the grain boundaries or obstacles is related to the low activation volume under the high Z deformation conditions at high strain （ε=0.6） while the fine DRX grains coarsed is the main reason for the high activation volume at low Z under the same strain conditions.
基金the support by the National Natural Science Foundations of China (Nos.50835003,50805047 and 10972078)National High Technology Research and Development Program of China (No.2009AA04Z421)+1 种基金the support by Shanghai Chenguang Planning Project(No.2008CG36)Ph.D. Programs Foundation of Ministry of Education of China(No.20090101120021)
文摘The creep behavior of the plasma sprayed NiCr and NiCrA1 coating/Nickel alloy 690 substrate systems at 1033 K was investigated. Results showed that there was almost no difference in the creep lives between the NiCr and NiCrA1 coated specimens at a given stress level, since the contents of Cr used in the NiCr and NiCrA1 powders are almost same. The relationship between the minimum creep rate and the applied stress followed the well-known Norton＇s power law, εmin=Aσ^n, with the values of A=2.66×10^-16 MPa^-n·h^-1 and n=6.48. The relation between the applied stress and time to rupture of the coated specimens can be estimated by using Larson-Miller equation. The θ projection method can be used to accurately characterize the creep behavior of the coated specimens.
基金The project supported by the National Natural Science Foundation of China and Doctorial Fund
文摘A transient molecular network model is built to describe the non- linear viscoelasticity of polymers by considering the effect of entanglement loss and regeneration on the relaxation of molecular strands. It is an extension of previous network theories. The experimental data on three thermoplastic polymers (ABS, PVC and PA6) obtained under various loading conditions are used to test the model. Agreement between the theoretical and experimental curves shows that the suggested model can describe successfully the relaxation behavior of the thermoplastic polymers under different loading rates by using relatively few relaxation modes. Thus the mi- cromechanism responsible for strain-rate dependence of relaxation process and the origin of nonlinear viscoelasticity may be disclosed.
基金Supported bythe Joint Earthquake Science Foundation of China(grant 199061) Contribution No.2005B0011 of the Institute of Geology,China Earthquake Administration.
文摘According to the ＂Netlike Plastic-Flow （NPF）＂ continental dynamics model, the transition of the deformation regime from brittle in shallow layers to ductile in deep layers in the lithosphere, and the controlling effect of NPF in the lower lithosphere result in intraplate multilayer tectonic deformation. NPF is a viscous （plastic） flow accompanied by shear strain localization, forming a plastic-flow network in the lower lithosphere. The strain rates in the seismogeulc layer can be estimated using the ＂earthquake-recurrence-interval＂ method, in which the strain rate is calculated in terms of the recurrence interval of two sequential earthquakes and the seismic probability of the second earthquake. The strains in the lower lithosphere are estimated using the ＂conjugate-angle＂ method, which takes the relationship between the conjugate angles and the compressive strains of the network, and calculates the characteristic strain rates in this layer from the strains and the durations of deformation inferred. The contour map of characteristic maximum principal compressive strain rates in the lower lithosphere in central-eastern Asia given in the paper shows strain rates with magnitudes on the order of 10^-15 - 10^-14/s in this region. The strain rates within the plastic-flow belts, which control seismic activities in the seismogeulc layer, are greater than the characteristic strain rates of the network and, in addition, the strain rates and seismic activities in the seismogeulc layer are also influenced by other factors, including the directive action of driving boundary along the upper crust, the effects of plastic-flow waves and the existence of the transitional weak layer distributed discontinuously between the upper and lower layers. The comparison between the strain rates in the seismogeulc layer and the characteristic strain rates in the lower lithosphere for 11 potential hypocenter areas in the region from the Qinghai-Xizang （Tibet） plateau to the North China plain indicates that, except for
