On the basis of continuum mechanics and the Mori-Tanaka mean field theory, a micro-mechanical flow stress model that considered both the transformation-induced plasticity (TRIP) effect and the inelastic strain recov...On the basis of continuum mechanics and the Mori-Tanaka mean field theory, a micro-mechanical flow stress model that considered both the transformation-induced plasticity (TRIP) effect and the inelastic strain recovery behavior of TRIP multiphase steels was presented. The relation between the volume fraction of constituent phases and plastic strain was introduced to characterize the transformation-induced plasticity effect of TRIP steels. Loading-unloading-reloading uniaxial tension tests of TRIP600 steel were carried out and the strain recovery behavior after unloading was analyzed. From the experimental data, an empirical elastic modulus expression is extracted to characterize the inelastic strain recovery. A comparison of the predicted flow stress with the experimental data shows a good agreement. The mechanism of the transformation-induced plasticity effect and the inelastic recovery effect acting on the flow stress is also discussed in detail.展开更多
Effects of deformation temperature on the mechanical properties and microstructure of lean duplex stainless steels B2102 and S32101 have been investigated. It was found that the strength decreased continuously with in...Effects of deformation temperature on the mechanical properties and microstructure of lean duplex stainless steels B2102 and S32101 have been investigated. It was found that the strength decreased continuously with increases in temperature from -60 ℃ to 100 ℃. The strength of S32101 was higher than that of B2102 owing to its higher nitrogen content. Plasticity of B2102 increased with an increase in deformation temperature from - 60 ℃ and reached the optimal elongation ratio of 49% - 54% after deformation at 20 - 50 ^(2. Martensite transformation was observed during deformation due to the transformation-induced plasticity effect. The optimal elongation was achieved at deformation temperatures close to the Md(3O/50) temperatures of 62 ℃ and 6 ℃ for B2102 and S32101. respectively.展开更多
Grapevine embodies a fascinating species as regards phenotypic plasticity and genotype-per-environment interactions.The terroir,namely the set of agri-environmental factors to which a variety is subjected,can influenc...Grapevine embodies a fascinating species as regards phenotypic plasticity and genotype-per-environment interactions.The terroir,namely the set of agri-environmental factors to which a variety is subjected,can influence the phenotype at the physiological,molecular,and biochemical level,representing an important phenomenon connected to the typicality of productions.We investigated the determinants of plasticity by conducting a field-experiment where all terroir variables,except soil,were kept as constant as possible.We isolated the effect of soils collected from different areas,on phenology,physiology,and transcriptional responses of skin and flesh of a red and a white variety of great economic value:Corvina and Glera.Molecular results,together with physio-phenological parameters,suggest a specific effect of soil on grapevine plastic response,highlighting a higher transcriptional plasticity of Glera in respect to Corvina and a marked response of skin compared to flesh.Using a novel statistical approach,we identified clusters of plastic genes subjected to the specific influence of soil.These findings could represent an issue of applicative value,posing the basis for targeted agricultural practices to enhance the desired characteristics for any soil/cultivar combination,to improve vineyards management for a better resource usage and to valorize vineyards uniqueness maximizing the terroir-effect.展开更多
In the present study, a rat model of chronic neuropathic pain was established by ligation of the sciatic nerve and a model of learning and memory impairment was established by ovariectomy to investigate the analgesic ...In the present study, a rat model of chronic neuropathic pain was established by ligation of the sciatic nerve and a model of learning and memory impairment was established by ovariectomy to investigate the analgesic effect of repeated electroacupuncture stimulation at bilateral Zusanfi (ST36) and Yanglingquan (GB34). In addition, associated synaptic changes in neurons in the paraventricular nucleus of the hypothalamus were examined. Results indicate that the thermal pain threshold (paw withdrawal latency) was significantly increased in rats subjected to 2-week electroacupuncture intervention compared with 2-day electroacupuncture, but the analgesic effect was weakened remarkably in ovariectomized rats with chronic constrictive injury. 2-week electroacupuncture intervention substantially reversed the chronic constrictive injury-induced increase in the synaptic cleft width and thinning of the postsynaptic density. These findings indicate that repeated electroacupuncture at bilateral Zusanfi and Yanglingquan has a cumulative analgesic effect and can effectively relieve chronic neuropathic pain by remodeling the synaptic structure of the hypothalamic paraventricular nucleus.展开更多
Plastic instability, called Portevin-Le-Chatelier(PLC) effect, manifests itself as an unstable plastic flow during tensile tests of structural materials. This phenomenon has a strong influence on diverse properties, l...Plastic instability, called Portevin-Le-Chatelier(PLC) effect, manifests itself as an unstable plastic flow during tensile tests of structural materials. This phenomenon has a strong influence on diverse properties, leading to unexpected vulnerabilities in the service environment.Among various magnesium-based alloys, PLC phenomenon is most prominently observed in the Mg-Mn-Nd alloy under elevated temperature and low strain rate conditions. An important aim of the study is to clarify and compare the significance of the RE and Ca addition, which are known to cause a formation of a largely weakened non-basal type texture, in the occurrence of plastic instability. Due to the PLC phenomenon, there is a risk of weakening texture and formability improvement by the addition of RE and Ca elements in Mg alloys. Based on the understanding of the role of Nd to the PLC phenomenon in Mg-Mn alloy identified in previous studies, the PLC characteristics according to alloying elements and deformation conditions were compared and analyzed. To identify the micromechanical mechanisms of the PLC phenomenon, varies in the microstructure and mechanical properties during deformation of Mg-Mn binary and Ca or Nd-containing Mg-Mn-based ternary alloys in various conditions were systemically analyzed. The addition of Ca did not show a marked PLC effect due to the formation of low number density Mn-Ca and Ca-Ca solute clusters and an unbalanced Mn:Ca ratio. In contrast, the addition of Nd leads to the formation of a higher number density of Nd-Nd and Mn-Nd solute clusters than that of Ca-Ca and Mn-Ca solute clusters of the Mg-Mn-Ca alloy, resulting in a stable solute-dislocation interaction atmosphere under specific ranges of deformation temperature and strain rate. The deformation in the regime of PLC phenomenon, results in a decrease in ductility and an increase in strength, despite deformation at elevated temperatures with maintaining the weakened texture.展开更多
Effect of austempering on the transformation induced plasticity (TRIP) of hot rolled multiphase steel was investigated. Polygonal ferrite, granular bainite, and a large amount of stabilized retained austenite could ...Effect of austempering on the transformation induced plasticity (TRIP) of hot rolled multiphase steel was investigated. Polygonal ferrite, granular bainite, and a large amount of stabilized retained austenite could be obtained in the hot rolled multiphase steel. Strain induced martensite transformation (SIMT) of retained austenite and TRIP effectively occur under straining owing to austempering after hot rolling, and mechanical properties of the present steel remain at a relatively high constant value for austempering at 400℃. The mechanical properties of the steel exhibited a good combination of tensile strength (791MPa) and total elongation (36%) because the stability of retained austenite is optimal when the steel is held for 20min.展开更多
Temperature compensatory effect, which quantifies the increase in cumulative air temperature from soil temperature increase caused by mulching, provides an effective method for incorporating soil temperature into crop...Temperature compensatory effect, which quantifies the increase in cumulative air temperature from soil temperature increase caused by mulching, provides an effective method for incorporating soil temperature into crop models. In this study, compensated temperature was integrated into the AquaCrop model to investigate the capability of the compensatory effect to improve assessment of the promotion of maize growth and development by plastic film mulching(PM). A three-year experiment was conducted from2014 to 2016 with two maize varieties(spring and summer) and two mulching conditions(PM and non-mulching(NM)), and the AquaCrop model was employed to reproduce crop growth and yield responses to changes in NM, PM, and compensated PM. A marked difference in soil temperature between NM and PM was observed before 50 days after sowing(DAS) during three growing seasons. During sowing–emergence and emergence–tasseling, the increase in air temperature was proportional to the compensatory coefficient, with spring maize showing a higher compensatory temperature than summer maize. Simulation results for canopy cover(CC) were generally in good agreement with the measurements, whereas predictions of aboveground biomass and grain yield under PM indicated large underestimates from 60 DAS to the end of maturity. Simulations of spring maize biomass and yield showed general increase based on temperature compensation, accompanied by improvement in modeling accuracy, with RMSEs decreasing from 2.5 to 1.6 t ha^(-1)and from 4.1 t to 3.4 t ha^(-1). Improvement in biomass and yield simulation was less pronounced for summer than for spring maize, implying that crops grown during low-temperature periods would benefit more from the compensatory effect. This study demonstrated the effectiveness of the temperature compensatory effect to improve the performance of the AquaCrop model in simulating maize growth under PM practices.展开更多
The Bauschinger and size effects in the thinfilm plasticity theory arising from the defect-energy of geometrically necessary dislocations (GNDs) are analytically investigated in this paper. Firstly, this defect-ener...The Bauschinger and size effects in the thinfilm plasticity theory arising from the defect-energy of geometrically necessary dislocations (GNDs) are analytically investigated in this paper. Firstly, this defect-energy is deduced based on the elastic interactions of coupling dislocations (or pile-ups) moving on the closed neighboring slip plane. This energy is a quadratic function of the GNDs density, and includes an elastic interaction coefficient and an energetic length scale L. By incorporating it into the work- conjugate strain gradient plasticity theory of Gurtin, an energetic stress associated with this defect energy is obtained, which just plays the role of back stress in the kinematic hardening model. Then this back-stress hardening model is used to investigate the Bauschinger and size effects in the tension problem of single crystal Al films with passivation layers. The tension stress in the film shows a reverse dependence on the film thickness h. By comparing it with discrete-dislocation simulation results, the length scale L is determined, which is just several slip plane spacing, and accords well with our physical interpretation for the defect- energy. The Bauschinger effect after unloading is analyzed by combining this back-stress hardening model with a friction model. The effects of film thickness and pre-strain on the reversed plastic strain after unloading are quantified and qualitatively compared with experiment results.展开更多
This paper presents an improved strain-softening constitutive model considering the effect of crack deformation based on the triaxial cyclic loading and unloading test results.The improved model assumes that total str...This paper presents an improved strain-softening constitutive model considering the effect of crack deformation based on the triaxial cyclic loading and unloading test results.The improved model assumes that total strain is a combination of plastic,elastic,and crack strains.The constitutive relationship between the crack strain and the stress was further derived.The evolutions of mechanical parameters,i.e.strength parameters,dilation angle,unloading elastic modulus,and deformation parameters of crack,with the plastic strain and confining pressure were studied.With the increase in plastic strain,the cohesion,friction angle,dilation angle,and crack Poisson's ratio initially increase and subsequently decrease,and the unloading elastic modulus and the crack elastic modulus nonlinearly decrease.The increasing confining pressure enhances the strength and unloading elastic modulus,and decreases the dilation angle and Poisson's ratio of the crack.The theoretical triaxial compressive stress-strain curves were compared with the experimental results,and they present a good agreement with each other.The improved constitutive model can well reflect the nonlinear mechanical behavior of granite.展开更多
The paper concerns the issue of size law,localized deformation and dilation or compaction due to shear localization. It is assumed that the shear localization initiates at the peak shear stress in the form of single s...The paper concerns the issue of size law,localized deformation and dilation or compaction due to shear localization. It is assumed that the shear localization initiates at the peak shear stress in the form of single shear band,and based on gradient-dependent plasticity,an analytical solution on size effect or snap-back is obtained. The results show that the post peak response becomes steeper and even exhibits snap-back with increasing of length. For small specimen,the relative shear displacement when specimen failure occurs is lower than that of larger specimen and the shear stress-relative displacement curve becomes steeper. The theoretical solution on non-uniformity of strains in shear band is obtained and evolution of the relative shear displacement is represented. By resorting to the linear relation between local plastic shear strain and local plastic volumetric strain,the dilation and compaction within shear band are analyzed. Relation between apparent shear strain and apparent normal strain and relation between shear displacement and vertical displacement are established.展开更多
An investigation on the plastic behavior of AZ31 magnesium alloy under ultrasonic vibration(with a frequency of 15 kHz and a maximum output of 2 kW) during the process of tension at room temperature was conducted to...An investigation on the plastic behavior of AZ31 magnesium alloy under ultrasonic vibration(with a frequency of 15 kHz and a maximum output of 2 kW) during the process of tension at room temperature was conducted to reveal the volume effect of the vibrated plastic deformation of AZ31.The characteristics of mechanical properties and microstructures of AZ31 under routine and vibrated tensile processes with different amplitudes were compared.It is found that ultrasonic vibration has a remarkable influence on the plastic behavior of AZ31 which can be summarized into two opposite aspects:the softening effect which reduces the flow resistance and improves the plasticity,and the hardening effect which decreases the formability.When a lower amplitude or vibration energy is applied to the tensile sample,the softening effect dominates,leading to a decrease of AZ31 deformation resistance with an increase of formability.Under the application of a high-vibrating amplitude,the hardening effect dominates,resulting in the decline of plasticity and brittle fracture of the samples.展开更多
Detecting stress concentration, especially critical stress state leading to structure damage or failure, is one of the most important tasks of equipment diagnosis. Metal magnetic memory technique needs further researc...Detecting stress concentration, especially critical stress state leading to structure damage or failure, is one of the most important tasks of equipment diagnosis. Metal magnetic memory technique needs further research to evaluate stress concentration quantitatively due to ambiguous physical mechanism, though it has potential to detect early defects in ferromagnetic materials. Mild Q235 steel defective specimens in demagnetization state were loaded in tension up to visible necking, with magnetic memory signals measurement made at increasing stress levels. Magnetic signals varied greatly under first several loadings and subsequently tended to stability in the elastic region, which showed that the magnetization always approaches the anhysteretic magnetization curve and was explained by the theory of magnetomechanical effect. In the plastic stage, an abnormal wave occurred in the stress concentration zone and its height value was sensitive to plastic deformation levels and dependent on the distance between the probe and defect, in accordance with the simulation results based on the magnetic dipole model. Different magnetic signal characteristics in the elastic-plastic region indicate that the magnetic memory technique can identify macroyielding and early damage, which is of profound significance for ensuring safe operation of equipment in service.展开更多
The relations of bulk modulus, shear modulus, Young's modulus and the Poisson's ratio with porosity of foam plastics are determined by a three phase spheroidal model commonly used in Composite Mechanics. The r...The relations of bulk modulus, shear modulus, Young's modulus and the Poisson's ratio with porosity of foam plastics are determined by a three phase spheroidal model commonly used in Composite Mechanics. The results are compared with those using differential scheme. It is shown that the material properties derived from the present model normally are larger than those obtained by differential scheme for foam plastics with identical porosity. The differences in shear moduli and Young's moduli obtained by the two methods are small but they are larger for bulk moduli of incompressible matrix and Poisson's ratios. The Young's moduli of high density foam plastics derived by the present model agree better with experimental ones.展开更多
Recent studies have shown that the size of microvoids has a significant effect on the void growth rate.The purpose of this paper is to explore whether the void size effect can influence the plastic flow localization i...Recent studies have shown that the size of microvoids has a significant effect on the void growth rate.The purpose of this paper is to explore whether the void size effect can influence the plastic flow localization in ductile materials.We have used the extended Gurson's dilatational plasticity theory,which accounts for the void size effect,to study the plastic flow localization in porous solids with long cylindrical voids.The localization model of Rice is adopted,in which the material inside the band may display a different response from that outside the band at the incipient plastic flow localization.The present study shows that it has little effect on the shear band angle.展开更多
Based on approximate theoretical analyses on a typical spherical cellcontaining a spherical rnicrovoid, the influences of matrix materials' microscopic scale on themacroscopic constitutive potential theory of poro...Based on approximate theoretical analyses on a typical spherical cellcontaining a spherical rnicrovoid, the influences of matrix materials' microscopic scale on themacroscopic constitutive potential theory of porous material and microvoid growth have beeninvestigated in detail. By assuming that the plastic: deformation behavior of matrix materialsfollows the strain gradient (SG) plastic theory involving the stretch and rotation gradients , theratio (λ = l/a) of the matrix materials' intrinsic characteristic length l to the micro-void radiusa is introduced into the plastic constitutive potential and the void growth law. The presentresults indicate that, when the radius a of microvoids is comparable with the intrinsiccharacteristic length l of the matrix materials, the influence of microscopic size effect on neitherthe constitutive potential nor the micro-void evolution predicted can be ignored. And when the voidradius a is much lager than the intrinsic characteristic length l of the matrix materials, thepresent model can retrogress automatically to the improved Gur-son model that takes into account thestrain hardening effect of matrix materials.展开更多
Urothelial carcinoma(UC) of the bladder is characterized by high recurrence rate where a subset of these cells undergoes transition to deadly muscle invasive disease and later metastasizes. Urothelial cancer stem cell...Urothelial carcinoma(UC) of the bladder is characterized by high recurrence rate where a subset of these cells undergoes transition to deadly muscle invasive disease and later metastasizes. Urothelial cancer stem cells(UroC SCs), a tumor subpopulation derived from trans-formation of urothelial stem cells, are responsible for heterogeneous tumor formation and resistance to systemic treatment in UC of the bladder. Although the precise reason for pathophysiologic spread of tumor is not clear, transcriptome analysis of microdissected cancer cells expressing multiple progenitor/stem cell markers validates the upregulation of genes that derive epithelial-to-mesenchymal transition. Experimental studies on human bladder cancer xenografts describe the mechanistic functions and regulation of epithelial plasticity for its cancer-restraining effects. It has been further examined to be associated with the recruitment of a pool of Uro CSCs into cell division in response to damages induced by adjuvant therapies. This paper also discusses the various probable therapeutic approaches to attenuate the progressive manifestation of chemoresistance by co-administration of inhibitors of epithelial plasticity and chemotherapeutic drugs by abrogating the early tumor repopulation as well as killing differentiated cancer cells.展开更多
This paper proposes a new experimental method of quantitative plastic deformation analysis by means of the thermoplastic effect. The incremental plastic strain distribution for a single shear specimen was obtained by ...This paper proposes a new experimental method of quantitative plastic deformation analysis by means of the thermoplastic effect. The incremental plastic strain distribution for a single shear specimen was obtained by using this method.展开更多
In our previous study, metals have been used as absorbers in the clear plastic laser transmission welding. The effects of metal thermal conductivity on the welding quality are investigated in the present work. Four me...In our previous study, metals have been used as absorbers in the clear plastic laser transmission welding. The effects of metal thermal conductivity on the welding quality are investigated in the present work. Four metals with distinctly different thermal conductivities, i.e., titanium, nickel, molybdenum, and copper, are selected as light absorbers. The lap welding is conducted with an 808 nm diode laser and simulation experiments are also conducted. Nickel electroplating test is carried out to minimize the side-effects from different light absorptivities of different metals. The results show that the welding with an absorber of higher thermal conductivity can accommodate higher laser input power before smoking, which produces a wider and stronger welding seam.The positive role of the higher thermal conductivity can be attributed to the fact that a desirable thermal field distribution for the molecular diffusion and entanglement is produced from the case with a high thermal conductivity.展开更多
Hard coatings have been widely applied to enhance tribological performance of mechanical components.However,it was predicted that thin hard coatings may have a weakening effect which could reduce the coating/substrate...Hard coatings have been widely applied to enhance tribological performance of mechanical components.However,it was predicted that thin hard coatings may have a weakening effect which could reduce the coating/substrate system’s resistance to plastic yielding compared with the uncoated substrate material.In this paper,analytical simulation is utilized to investigate the origin of weakening effect.The functions of material mechanical properties and coating thickness on the weakening effect are theoretically investigated.Partial-unloading spherical nanoindentation tests are performed on tungsten coated single crystalline silicon and copper to acquire the stress-strain curves and compared with the uncoated cases.The experimental results are in consistence with the analytical solutions,demonstrating the presence of weakening effect.展开更多
The microstructure of crystal defects,e.g.,dislocation patterns,are not arbitrary,and it is possible that some of them may be related to the microstructure of crystals itself,i.e.,the lattice structure.We call those d...The microstructure of crystal defects,e.g.,dislocation patterns,are not arbitrary,and it is possible that some of them may be related to the microstructure of crystals itself,i.e.,the lattice structure.We call those dislocation patterns or substructures that are related to the corresponding crystal microstructure as the Geometrically Compatible Dislocation Patterns(GCDP).Based on this notion,we have developed a Multiscale Crystal Defect Dynamics(MCDD)to model crystal plasticity without or with minimum empiricism.In this work,we employ the multiscale dislocation pattern dynamics,i.e.,MCDD,to simulate crystal plasticity in body-centered cubic(BCC)single crystals,mainlyα-phase Tantalum(α-Ta)single crystals.The main novelties of the work are:(1)We have successfully simulated crystal plasticity at micron scale without any empirical parameter inputs;(2)We have successfully employed MCDD to perform direct numerical simulation of inelastic hysteresis of the BCC crystal;(3)We have used MCDD crystal plasticity model to demonstrate the size-effect of crystal plasticity and(4)We have captured cross-slip which may lead to size-effect.展开更多
基金supported by the National Natural Science Foundation of China (No.50705067)the Ph.D. Programs Foundation of the Ministry of Education of China (No.20070247013)
文摘On the basis of continuum mechanics and the Mori-Tanaka mean field theory, a micro-mechanical flow stress model that considered both the transformation-induced plasticity (TRIP) effect and the inelastic strain recovery behavior of TRIP multiphase steels was presented. The relation between the volume fraction of constituent phases and plastic strain was introduced to characterize the transformation-induced plasticity effect of TRIP steels. Loading-unloading-reloading uniaxial tension tests of TRIP600 steel were carried out and the strain recovery behavior after unloading was analyzed. From the experimental data, an empirical elastic modulus expression is extracted to characterize the inelastic strain recovery. A comparison of the predicted flow stress with the experimental data shows a good agreement. The mechanism of the transformation-induced plasticity effect and the inelastic recovery effect acting on the flow stress is also discussed in detail.
基金sponsored by the Project of Shanghai Industrial Application of New and HighTechnologies in 2009
文摘Effects of deformation temperature on the mechanical properties and microstructure of lean duplex stainless steels B2102 and S32101 have been investigated. It was found that the strength decreased continuously with increases in temperature from -60 ℃ to 100 ℃. The strength of S32101 was higher than that of B2102 owing to its higher nitrogen content. Plasticity of B2102 increased with an increase in deformation temperature from - 60 ℃ and reached the optimal elongation ratio of 49% - 54% after deformation at 20 - 50 ^(2. Martensite transformation was observed during deformation due to the transformation-induced plasticity effect. The optimal elongation was achieved at deformation temperatures close to the Md(3O/50) temperatures of 62 ℃ and 6 ℃ for B2102 and S32101. respectively.
基金The study was carried out within the Agritech National Research Center and received funding from the European Union Next-Generation EU(PIANO NAZIONALE DI RIPRESA E RESILIENZA(PNRR)-MISSIONE 4 COMPONENTE 2,INVESTIMENTO 1.4-D.D.103217/06/2022,CN00000022).
文摘Grapevine embodies a fascinating species as regards phenotypic plasticity and genotype-per-environment interactions.The terroir,namely the set of agri-environmental factors to which a variety is subjected,can influence the phenotype at the physiological,molecular,and biochemical level,representing an important phenomenon connected to the typicality of productions.We investigated the determinants of plasticity by conducting a field-experiment where all terroir variables,except soil,were kept as constant as possible.We isolated the effect of soils collected from different areas,on phenology,physiology,and transcriptional responses of skin and flesh of a red and a white variety of great economic value:Corvina and Glera.Molecular results,together with physio-phenological parameters,suggest a specific effect of soil on grapevine plastic response,highlighting a higher transcriptional plasticity of Glera in respect to Corvina and a marked response of skin compared to flesh.Using a novel statistical approach,we identified clusters of plastic genes subjected to the specific influence of soil.These findings could represent an issue of applicative value,posing the basis for targeted agricultural practices to enhance the desired characteristics for any soil/cultivar combination,to improve vineyards management for a better resource usage and to valorize vineyards uniqueness maximizing the terroir-effect.
基金supported by the National Natural Science Foundation of China,No.30472241,90709031 and 30973796the National Basic Research Program of China for Traditional Chinese Medicine Theory("973" Program),No.2007CB512505+1 种基金the Natural Foundation of Hainan Province(No.310054)a grant from the Health Department of Hainan Province(QiongWei 2010-45)
文摘In the present study, a rat model of chronic neuropathic pain was established by ligation of the sciatic nerve and a model of learning and memory impairment was established by ovariectomy to investigate the analgesic effect of repeated electroacupuncture stimulation at bilateral Zusanfi (ST36) and Yanglingquan (GB34). In addition, associated synaptic changes in neurons in the paraventricular nucleus of the hypothalamus were examined. Results indicate that the thermal pain threshold (paw withdrawal latency) was significantly increased in rats subjected to 2-week electroacupuncture intervention compared with 2-day electroacupuncture, but the analgesic effect was weakened remarkably in ovariectomized rats with chronic constrictive injury. 2-week electroacupuncture intervention substantially reversed the chronic constrictive injury-induced increase in the synaptic cleft width and thinning of the postsynaptic density. These findings indicate that repeated electroacupuncture at bilateral Zusanfi and Yanglingquan has a cumulative analgesic effect and can effectively relieve chronic neuropathic pain by remodeling the synaptic structure of the hypothalamic paraventricular nucleus.
基金financial support of German Research Foundation (DFG)(Grant Nr. YI103/3-1 and AL1343/8-1)。
文摘Plastic instability, called Portevin-Le-Chatelier(PLC) effect, manifests itself as an unstable plastic flow during tensile tests of structural materials. This phenomenon has a strong influence on diverse properties, leading to unexpected vulnerabilities in the service environment.Among various magnesium-based alloys, PLC phenomenon is most prominently observed in the Mg-Mn-Nd alloy under elevated temperature and low strain rate conditions. An important aim of the study is to clarify and compare the significance of the RE and Ca addition, which are known to cause a formation of a largely weakened non-basal type texture, in the occurrence of plastic instability. Due to the PLC phenomenon, there is a risk of weakening texture and formability improvement by the addition of RE and Ca elements in Mg alloys. Based on the understanding of the role of Nd to the PLC phenomenon in Mg-Mn alloy identified in previous studies, the PLC characteristics according to alloying elements and deformation conditions were compared and analyzed. To identify the micromechanical mechanisms of the PLC phenomenon, varies in the microstructure and mechanical properties during deformation of Mg-Mn binary and Ca or Nd-containing Mg-Mn-based ternary alloys in various conditions were systemically analyzed. The addition of Ca did not show a marked PLC effect due to the formation of low number density Mn-Ca and Ca-Ca solute clusters and an unbalanced Mn:Ca ratio. In contrast, the addition of Nd leads to the formation of a higher number density of Nd-Nd and Mn-Nd solute clusters than that of Ca-Ca and Mn-Ca solute clusters of the Mg-Mn-Ca alloy, resulting in a stable solute-dislocation interaction atmosphere under specific ranges of deformation temperature and strain rate. The deformation in the regime of PLC phenomenon, results in a decrease in ductility and an increase in strength, despite deformation at elevated temperatures with maintaining the weakened texture.
基金supported by the National Natural Science Foundation of China(No.50334010)the Doctor Degree Thesis Subsidization Item of Northeastern University(No.200302).
文摘Effect of austempering on the transformation induced plasticity (TRIP) of hot rolled multiphase steel was investigated. Polygonal ferrite, granular bainite, and a large amount of stabilized retained austenite could be obtained in the hot rolled multiphase steel. Strain induced martensite transformation (SIMT) of retained austenite and TRIP effectively occur under straining owing to austempering after hot rolling, and mechanical properties of the present steel remain at a relatively high constant value for austempering at 400℃. The mechanical properties of the steel exhibited a good combination of tensile strength (791MPa) and total elongation (36%) because the stability of retained austenite is optimal when the steel is held for 20min.
基金supported by the National Natural Science Foundation of China (51909228 and 52209071)the “High-level Talents Support Program” of Yangzhou University+2 种基金“Chunhui Plan” Cooperative Scientific Research Project of Ministry of Education of China (HZKY20220115)the China Postdoctoral Science Foundation (2020M671623)the “Blue Project” of Yangzhou University。
文摘Temperature compensatory effect, which quantifies the increase in cumulative air temperature from soil temperature increase caused by mulching, provides an effective method for incorporating soil temperature into crop models. In this study, compensated temperature was integrated into the AquaCrop model to investigate the capability of the compensatory effect to improve assessment of the promotion of maize growth and development by plastic film mulching(PM). A three-year experiment was conducted from2014 to 2016 with two maize varieties(spring and summer) and two mulching conditions(PM and non-mulching(NM)), and the AquaCrop model was employed to reproduce crop growth and yield responses to changes in NM, PM, and compensated PM. A marked difference in soil temperature between NM and PM was observed before 50 days after sowing(DAS) during three growing seasons. During sowing–emergence and emergence–tasseling, the increase in air temperature was proportional to the compensatory coefficient, with spring maize showing a higher compensatory temperature than summer maize. Simulation results for canopy cover(CC) were generally in good agreement with the measurements, whereas predictions of aboveground biomass and grain yield under PM indicated large underestimates from 60 DAS to the end of maturity. Simulations of spring maize biomass and yield showed general increase based on temperature compensation, accompanied by improvement in modeling accuracy, with RMSEs decreasing from 2.5 to 1.6 t ha^(-1)and from 4.1 t to 3.4 t ha^(-1). Improvement in biomass and yield simulation was less pronounced for summer than for spring maize, implying that crops grown during low-temperature periods would benefit more from the compensatory effect. This study demonstrated the effectiveness of the temperature compensatory effect to improve the performance of the AquaCrop model in simulating maize growth under PM practices.
基金supported by the National Natural Science Foundation of China (10772096)
文摘The Bauschinger and size effects in the thinfilm plasticity theory arising from the defect-energy of geometrically necessary dislocations (GNDs) are analytically investigated in this paper. Firstly, this defect-energy is deduced based on the elastic interactions of coupling dislocations (or pile-ups) moving on the closed neighboring slip plane. This energy is a quadratic function of the GNDs density, and includes an elastic interaction coefficient and an energetic length scale L. By incorporating it into the work- conjugate strain gradient plasticity theory of Gurtin, an energetic stress associated with this defect energy is obtained, which just plays the role of back stress in the kinematic hardening model. Then this back-stress hardening model is used to investigate the Bauschinger and size effects in the tension problem of single crystal Al films with passivation layers. The tension stress in the film shows a reverse dependence on the film thickness h. By comparing it with discrete-dislocation simulation results, the length scale L is determined, which is just several slip plane spacing, and accords well with our physical interpretation for the defect- energy. The Bauschinger effect after unloading is analyzed by combining this back-stress hardening model with a friction model. The effects of film thickness and pre-strain on the reversed plastic strain after unloading are quantified and qualitatively compared with experiment results.
基金financially supported by the National Natural Science Foundation of China(Grant No.52074269).
文摘This paper presents an improved strain-softening constitutive model considering the effect of crack deformation based on the triaxial cyclic loading and unloading test results.The improved model assumes that total strain is a combination of plastic,elastic,and crack strains.The constitutive relationship between the crack strain and the stress was further derived.The evolutions of mechanical parameters,i.e.strength parameters,dilation angle,unloading elastic modulus,and deformation parameters of crack,with the plastic strain and confining pressure were studied.With the increase in plastic strain,the cohesion,friction angle,dilation angle,and crack Poisson's ratio initially increase and subsequently decrease,and the unloading elastic modulus and the crack elastic modulus nonlinearly decrease.The increasing confining pressure enhances the strength and unloading elastic modulus,and decreases the dilation angle and Poisson's ratio of the crack.The theoretical triaxial compressive stress-strain curves were compared with the experimental results,and they present a good agreement with each other.The improved constitutive model can well reflect the nonlinear mechanical behavior of granite.
基金Supported by the National Natural Science Foundation of China(50309004)。
文摘The paper concerns the issue of size law,localized deformation and dilation or compaction due to shear localization. It is assumed that the shear localization initiates at the peak shear stress in the form of single shear band,and based on gradient-dependent plasticity,an analytical solution on size effect or snap-back is obtained. The results show that the post peak response becomes steeper and even exhibits snap-back with increasing of length. For small specimen,the relative shear displacement when specimen failure occurs is lower than that of larger specimen and the shear stress-relative displacement curve becomes steeper. The theoretical solution on non-uniformity of strains in shear band is obtained and evolution of the relative shear displacement is represented. By resorting to the linear relation between local plastic shear strain and local plastic volumetric strain,the dilation and compaction within shear band are analyzed. Relation between apparent shear strain and apparent normal strain and relation between shear displacement and vertical displacement are established.
基金supported by the Natural Science Foundation Project of Chongqing Science and Technology Commission,China (No.2009BB4186)
文摘An investigation on the plastic behavior of AZ31 magnesium alloy under ultrasonic vibration(with a frequency of 15 kHz and a maximum output of 2 kW) during the process of tension at room temperature was conducted to reveal the volume effect of the vibrated plastic deformation of AZ31.The characteristics of mechanical properties and microstructures of AZ31 under routine and vibrated tensile processes with different amplitudes were compared.It is found that ultrasonic vibration has a remarkable influence on the plastic behavior of AZ31 which can be summarized into two opposite aspects:the softening effect which reduces the flow resistance and improves the plasticity,and the hardening effect which decreases the formability.When a lower amplitude or vibration energy is applied to the tensile sample,the softening effect dominates,leading to a decrease of AZ31 deformation resistance with an increase of formability.Under the application of a high-vibrating amplitude,the hardening effect dominates,resulting in the decline of plasticity and brittle fracture of the samples.
基金supported by National Natural Science Foundation of China(Grant No. 10772061)Heilongjiang Provincial Natural Science Foundation of China(Grant No. A200907)Specialized Research Fundfor the Doctoral Program of Higher Education of China(Grant No.20092322120001)
文摘Detecting stress concentration, especially critical stress state leading to structure damage or failure, is one of the most important tasks of equipment diagnosis. Metal magnetic memory technique needs further research to evaluate stress concentration quantitatively due to ambiguous physical mechanism, though it has potential to detect early defects in ferromagnetic materials. Mild Q235 steel defective specimens in demagnetization state were loaded in tension up to visible necking, with magnetic memory signals measurement made at increasing stress levels. Magnetic signals varied greatly under first several loadings and subsequently tended to stability in the elastic region, which showed that the magnetization always approaches the anhysteretic magnetization curve and was explained by the theory of magnetomechanical effect. In the plastic stage, an abnormal wave occurred in the stress concentration zone and its height value was sensitive to plastic deformation levels and dependent on the distance between the probe and defect, in accordance with the simulation results based on the magnetic dipole model. Different magnetic signal characteristics in the elastic-plastic region indicate that the magnetic memory technique can identify macroyielding and early damage, which is of profound significance for ensuring safe operation of equipment in service.
基金Supported by the National Natural Science Foundation of China and Laboratory for Nonlinear Mechanics of Continuous Media,Institute of Mechanics,Chinese Academy of Sciences.
文摘The relations of bulk modulus, shear modulus, Young's modulus and the Poisson's ratio with porosity of foam plastics are determined by a three phase spheroidal model commonly used in Composite Mechanics. The results are compared with those using differential scheme. It is shown that the material properties derived from the present model normally are larger than those obtained by differential scheme for foam plastics with identical porosity. The differences in shear moduli and Young's moduli obtained by the two methods are small but they are larger for bulk moduli of incompressible matrix and Poisson's ratios. The Young's moduli of high density foam plastics derived by the present model agree better with experimental ones.
基金The project supported by the National Natural Science Foundation of China (10121202) and Ministry of Education,China (20020003023 and Key Grant Project 0306)
文摘Recent studies have shown that the size of microvoids has a significant effect on the void growth rate.The purpose of this paper is to explore whether the void size effect can influence the plastic flow localization in ductile materials.We have used the extended Gurson's dilatational plasticity theory,which accounts for the void size effect,to study the plastic flow localization in porous solids with long cylindrical voids.The localization model of Rice is adopted,in which the material inside the band may display a different response from that outside the band at the incipient plastic flow localization.The present study shows that it has little effect on the shear band angle.
基金the National Natural Science Foundation of China (No.A10102006)
文摘Based on approximate theoretical analyses on a typical spherical cellcontaining a spherical rnicrovoid, the influences of matrix materials' microscopic scale on themacroscopic constitutive potential theory of porous material and microvoid growth have beeninvestigated in detail. By assuming that the plastic: deformation behavior of matrix materialsfollows the strain gradient (SG) plastic theory involving the stretch and rotation gradients , theratio (λ = l/a) of the matrix materials' intrinsic characteristic length l to the micro-void radiusa is introduced into the plastic constitutive potential and the void growth law. The presentresults indicate that, when the radius a of microvoids is comparable with the intrinsiccharacteristic length l of the matrix materials, the influence of microscopic size effect on neitherthe constitutive potential nor the micro-void evolution predicted can be ignored. And when the voidradius a is much lager than the intrinsic characteristic length l of the matrix materials, thepresent model can retrogress automatically to the improved Gur-son model that takes into account thestrain hardening effect of matrix materials.
基金Supported by Department of Science and Technology,Govt.of India,No.SR/H0/HS/0113-2010
文摘Urothelial carcinoma(UC) of the bladder is characterized by high recurrence rate where a subset of these cells undergoes transition to deadly muscle invasive disease and later metastasizes. Urothelial cancer stem cells(UroC SCs), a tumor subpopulation derived from trans-formation of urothelial stem cells, are responsible for heterogeneous tumor formation and resistance to systemic treatment in UC of the bladder. Although the precise reason for pathophysiologic spread of tumor is not clear, transcriptome analysis of microdissected cancer cells expressing multiple progenitor/stem cell markers validates the upregulation of genes that derive epithelial-to-mesenchymal transition. Experimental studies on human bladder cancer xenografts describe the mechanistic functions and regulation of epithelial plasticity for its cancer-restraining effects. It has been further examined to be associated with the recruitment of a pool of Uro CSCs into cell division in response to damages induced by adjuvant therapies. This paper also discusses the various probable therapeutic approaches to attenuate the progressive manifestation of chemoresistance by co-administration of inhibitors of epithelial plasticity and chemotherapeutic drugs by abrogating the early tumor repopulation as well as killing differentiated cancer cells.
基金Sponsored by the National Natural Science Foundation of ChinaProject supported by Astronautics Foundation of China(Project number QH9319)
文摘This paper proposes a new experimental method of quantitative plastic deformation analysis by means of the thermoplastic effect. The incremental plastic strain distribution for a single shear specimen was obtained by using this method.
基金Supported by the National Key R&D Program of China under Grant No 2016YFA0401100the National Natural Science Foundation of China under Grant No 61575129the National High-Technology Research and Development Program of China under Grant No 2015AA021102
文摘In our previous study, metals have been used as absorbers in the clear plastic laser transmission welding. The effects of metal thermal conductivity on the welding quality are investigated in the present work. Four metals with distinctly different thermal conductivities, i.e., titanium, nickel, molybdenum, and copper, are selected as light absorbers. The lap welding is conducted with an 808 nm diode laser and simulation experiments are also conducted. Nickel electroplating test is carried out to minimize the side-effects from different light absorptivities of different metals. The results show that the welding with an absorber of higher thermal conductivity can accommodate higher laser input power before smoking, which produces a wider and stronger welding seam.The positive role of the higher thermal conductivity can be attributed to the fact that a desirable thermal field distribution for the molecular diffusion and entanglement is produced from the case with a high thermal conductivity.
基金Project supported by the National Natural Science Foundation of China(Grant No.51705533)the National Science and Technology Major Project of China(Grant No.2017-VII-0013-0110)+1 种基金the Fundamental Research Funds for the Central Universities,China(Grant No.2020YQJD17)the Tribology Science Fund of State Key Laboratory of Tribology(Grant No.SKLTKF18B15).
文摘Hard coatings have been widely applied to enhance tribological performance of mechanical components.However,it was predicted that thin hard coatings may have a weakening effect which could reduce the coating/substrate system’s resistance to plastic yielding compared with the uncoated substrate material.In this paper,analytical simulation is utilized to investigate the origin of weakening effect.The functions of material mechanical properties and coating thickness on the weakening effect are theoretically investigated.Partial-unloading spherical nanoindentation tests are performed on tungsten coated single crystalline silicon and copper to acquire the stress-strain curves and compared with the uncoated cases.The experimental results are in consistence with the analytical solutions,demonstrating the presence of weakening effect.
文摘The microstructure of crystal defects,e.g.,dislocation patterns,are not arbitrary,and it is possible that some of them may be related to the microstructure of crystals itself,i.e.,the lattice structure.We call those dislocation patterns or substructures that are related to the corresponding crystal microstructure as the Geometrically Compatible Dislocation Patterns(GCDP).Based on this notion,we have developed a Multiscale Crystal Defect Dynamics(MCDD)to model crystal plasticity without or with minimum empiricism.In this work,we employ the multiscale dislocation pattern dynamics,i.e.,MCDD,to simulate crystal plasticity in body-centered cubic(BCC)single crystals,mainlyα-phase Tantalum(α-Ta)single crystals.The main novelties of the work are:(1)We have successfully simulated crystal plasticity at micron scale without any empirical parameter inputs;(2)We have successfully employed MCDD to perform direct numerical simulation of inelastic hysteresis of the BCC crystal;(3)We have used MCDD crystal plasticity model to demonstrate the size-effect of crystal plasticity and(4)We have captured cross-slip which may lead to size-effect.