The controlling plastic deformation mechanisms(i.e.slip or twinning)and the structural crash performance of Mg alloys are strongly influenced by loading mode,texture and microstructure.This paper summarizes the main r...The controlling plastic deformation mechanisms(i.e.slip or twinning)and the structural crash performance of Mg alloys are strongly influenced by loading mode,texture and microstructure.This paper summarizes the main results from an experimental program to assess these effects for commercial Mg alloy extrusions(AM30 and AZ31),sheet(AZ31),and high pressure die castings(HPDC,AM50 and AM60).Uniaxial tensile and compressive tests were performed over a wide range of strain rate and temperature(i.e.0.00075–2800 s^(−1) and 100℃ to−150℃)using conventional servo-hydraulic and high-strain-rate universal test machines and a split-Hopkinson-bar(SHB)apparatus.In primarily-slip-dominant deformation,the true stress–strain curves showed approximate power-law behavior,and the effects of strain rate and temperature on yield strength could be approximately described by constitutive equations linearly dependent on the rate parameter,Tln(5.3×10^(7)/ɛ˙)where T is test temperature in Kelvin andɛ˙is strain rate in s^(−1).In primarily-twin-dominant deformation,the effects of strain rate and temperature on yield and initial flow stress were negligible or small from quasi-static to 2800 s^(−1) owing to the athermal characteristics of mechanical twinning;the effects may become more pronounced with exhaustion of twinning and increasing proportion of slip.展开更多
The experimental tests for limestone specimens at 700 °C in uniaxial compression were carried out to inves- tigate the mechanical effects of loading rates on limestone by using a MTS810 rock mechanics servo- cont...The experimental tests for limestone specimens at 700 °C in uniaxial compression were carried out to inves- tigate the mechanical effects of loading rates on limestone by using a MTS810 rock mechanics servo- controlled testing system considering the loading rate as a variable. The mechanical properties of limestone such as the stress-strain curve, variable characteristics of peak strength and the modulus of elasticity of limestone were studied under the strain rates ranging from 1.1 10à5 to 1.1 10à1 sà1. (1) Sharp decreases were shown for the peak strength and elastic modulus of limestone from 1.1 10à5 to 1.1 10à4 sà1 at 700 °C as well as a downward trend was shown from 1.1 10à4 to 1.1 10à1 sà1 with the rise of the strain rate. (2) The peak strain increased from 1.1 10à5 to 1.1 10à4 sà1, however, there was no obvious changes shown for the peak strain of limestone from 1.1 10à4 to 1.1 10à1 sà1. These results can provide valuable references for the rock blasting effect and design of mine.展开更多
The strain-temperature cross-sensitivity problem easily occurs in the engineering strain monitoring of the self-sensing embedded with fiber Bragg grating(FBG)sensors.In this work,a theoretical investigation of the str...The strain-temperature cross-sensitivity problem easily occurs in the engineering strain monitoring of the self-sensing embedded with fiber Bragg grating(FBG)sensors.In this work,a theoretical investigation of the strain-temperature cross-sensitivity has been performed using the temperature reference grating method.To experimentally observe and theoretically verify the problem,the substrate materials,the preloading technique,and the FBG initial central wavelength were taken as main parameters.And a series of sensitivity coefficients calibration tests and temperature compensation tests have been designed and carried out.It was found that when the FBG sensors were embedded on different substrates,their coefficients of the temperature sensitivity were significantly changed.Besides,the larger the coefficients of thermal expansion(CTE)of substrates were,the higher the temperature sensitivity coefficients would be.On the other hand,the effect of the preloading technique and FBG initial wavelength was negligible on both the strain monitoring and temperature compensation.In the case of similar substrates,we did not observe any difference between temperature sensitivity coefficients of the temperature compensation FBG with one free end or two free ends.The curves of the force along with temperature were almost overlapped with minor differences(less than 1%)gained by FBG sensors and pressure sensors,which verified the accuracy of the temperature compensation method.We suggest that this work can provide efficient solutions to the strain-temperature cross-sensitivity for engineering strain monitoring with the self-sensing element embedded with FBG sensors.展开更多
Pain sensation may appear under long-lasting mechanical stimulation. Although people have the experience that pain sensation generally decreases with time while the stimulation remains, the underlying mechanism remain...Pain sensation may appear under long-lasting mechanical stimulation. Although people have the experience that pain sensation generally decreases with time while the stimulation remains, the underlying mechanism remains elusive. We experimentally studied the thermal and strain rate- dependent viscoelastic behavior of skin in uniaxial stretch and numerically investigated the effects of temperature and strain rate on pain sensation. The results indicate that the viscosity of skin tissue decreases with increasing temperature and reducing strain rate, which subsequently decreases the discharge frequency of skin nociceptor and thus relieves the pain sensation. The results would contribute to the understanding of pain relief mechanism and optimizing for mechanical treatment.展开更多
A liquid modified photonic crystal fiber(PCF)integrated with an embedded directional coupler and multi-mode interferometer is fabricated by infiltrating three adjacent air holes of the innermost layer with standard 1....A liquid modified photonic crystal fiber(PCF)integrated with an embedded directional coupler and multi-mode interferometer is fabricated by infiltrating three adjacent air holes of the innermost layer with standard 1.48 refractive index liquids.The refractive index of the filled liquid is higher than that of background silica,which can not only support the transmitting rod modes but also the"liquid modified core"modes propagating between the PCF core and the liquid rods.Hence,the light propagating in the liquid modified core can be efficiently coupled into the satellite waveguides under the phase-matching conditions,resulting in a dramatic decrease of the resonant wavelength intensity.Furthermore,there is a multi-mode interference produced by modified core modes and rod modes.Such a compact(~0.91 cm)device integrated with an embedded coupler and interferometer is demonstrated for high-sensitivity simultaneous temperature(~14.72 nm∕℃)and strain(~13.01 pm∕με)measurement.展开更多
During high speed machining in the field of manufacture,chip formation is a severe plastic deformation process including large strain,high strain rate and high temperature.And the strain rate in high speed cutting pro...During high speed machining in the field of manufacture,chip formation is a severe plastic deformation process including large strain,high strain rate and high temperature.And the strain rate in high speed cutting process can be achieved to 105 s^（-1）.30CrMnSiNi2Asteel is a kind of important high-strength low-alloy structural steel with wide application range.Obtaining the dynamic mechanical properties of30CrMnSiNi2Aunder the conditions of high strain rate and high temperature is necessary to construct the constitutive relation model for high speed machining.The dynamic compressive mechanical properties of30CrMnSiNi2Asteel were studied using split Hopkinson pressure bar（SHPB）tests at 30-700°C and3000-10000s^（-1）.The stress-strain curves of 30CrMnSiNi2Asteel at different temperatures and strain rates were investigated,and the strain hardening effect and temperature effect were discussed.Experimental results show that 30CrMnSiNi2Ahas obvious temperature sensitivity at 300°C.Moreover,the flow stress decreased significantly with the increase of temperature.The strain hardening effect of the material at high strain rate is not significant with the increase of strain.The strain rate hardening effect is obvious with increasing the temperature.According to the experimental results,the established Johnson-Cook（J-C）constitutive model of 30CrMnSiNi2Asteel could be used at high strain rate and high temperature.展开更多
To study the effect of tempering temperature on strain hardening exponent and flow stress curve,one kind of 1000 MPa grade low carbon bainitic steel for construction machinery was designed,and the standard uniaxial te...To study the effect of tempering temperature on strain hardening exponent and flow stress curve,one kind of 1000 MPa grade low carbon bainitic steel for construction machinery was designed,and the standard uniaxial tensile tests were conducted at room temperature.A new flow stress model,which could predict the flow behavior of the tested steels at different tempering temperatures more efficiently,was established.The relationship between mobile dislocation density and strain hardening exponent was discussed based on the dislocation-stress relation.Arrhenius equation and an inverse proportional function were adopted to describe the mobile dislocation,and two mathematical models were established to describe the relationship between tempering temperature and strain hardening exponent.Nonlinear regression analysis was applied to the Arrhenius type model,hence,the activation energy was determined to be 37.6kJ/mol.Moreover,the square of correlation coefficient was 0.985,which indicated a high reliability between the fitted curve and experimental data.By comparison with the Arrhenius type curve,the general trend of the inverse proportional fitting curve was coincided with the experimental data points except of some fitting errors.Thus,the Arrhenius type model can be adopted to predict the strain hardening exponent at different tempering temperatures.展开更多
A coarse-grained AM50 alloy was used as a model alloy for investigation of constitutive behaviour,Charpy toughness and effect of stress state on deformation and failure of cast Mg alloys.The results provide critical m...A coarse-grained AM50 alloy was used as a model alloy for investigation of constitutive behaviour,Charpy toughness and effect of stress state on deformation and failure of cast Mg alloys.The results provide critical mechanical properties of a cast AM50 alloy for crashworthiness assessment and development of finite element simulation techniques.For cast Mg alloys,the effect of strain rate and temperature is larger on tensile strength than on compressive strength because twinning is more extensive in compression than in tension.The effect of strain rate on compressive strength is negligible because twinning activity of the cast Mg alloy is dominant.The load vs.deflection of Charpy specimens were measured for modelling,and the effect of loading rate and temperature on load of Charpy specimens is very small because part of the specimen is in compression.The equivalent strain to fracture of the cylindrical round notched tension specimen decreases with increasing stress triaxiality;though for the flat-grooved plane strain specimen,the equivalent fracture strain remains constant over the range of stress triaxiality investigated.Because the two different specimen geometries give rise to different Lode angle values,the test results show that the Lode angle parameter is an important parameter for deformation and fracture of Mg alloys.Finite element simulations of loading of the cylindrical notched-tension and Charpy specimens were carried out using a Lode-angle dependent von Mises model,and were found to provide a reasonable description of the load-displacement curves measured in the tests.For the flat-grooved plane strain specimens,the computations under-predicted the force-displacement response measured.展开更多
A new approach utilizing effects of dispersion in the high-order-mode fibers （HOMFs） to effectively discriminate changes in environmental temperature and axial strain is proposed and experimentally demonstrated. Exp...A new approach utilizing effects of dispersion in the high-order-mode fibers （HOMFs） to effectively discriminate changes in environmental temperature and axial strain is proposed and experimentally demonstrated. Experimental characterization of a HOMF-based fiber modal interferometer with a sandwich fiber structure exhibits excellent agreements with numerical simulation results. A Fourier transform method of interferometry in the spatial frequency domain is adopted to distinguish mode coupling between different core-guided modes. Distinct phase sensitivities of multiple dispersion peaks are extracted by employing a novel phase demodulation scheme to realize dual-parameter sensing.展开更多
Chaotic Brillouin optical correlation domain analysis(BOCDA)has been proposed and experimentally demonstrated with the advantage of high spatial resolution.However,it faces the same issue of the temperature and strain...Chaotic Brillouin optical correlation domain analysis(BOCDA)has been proposed and experimentally demonstrated with the advantage of high spatial resolution.However,it faces the same issue of the temperature and strain cross-sensitivity.In this paper,the simultaneous measurement of temperature and strain can be preliminarily achieved by analyzing the two Brillouin frequencies of the chaotic laser in a large-effective-area fiber(LEAF).A temperature resolution of 1℃ and a strain resolution of 20μξ can be obtained with a spatial resolution of 3.9cm.The actual temperature and strain measurement errors are 0.37℃ and 10μξ,respectively,which are within the maximum measurement errors.展开更多
A micro-segregation model of solute elements in mushy zone with δ/γ transformation during solidification was established based on the regular hexagon transverse cross section of dendrite shape proposed by finite dif...A micro-segregation model of solute elements in mushy zone with δ/γ transformation during solidification was established based on the regular hexagon transverse cross section of dendrite shape proposed by finite difference method under the non-equilibrium solidification condition. The model was used to calculate the non-equilibrium pseudo binary Fe-C phase diagram and the strain of steels induced by variation of temperature in brittle temperature range. On the basis of the phase diagram and the strain, the strain curve in brittle temperature range as a function of carbon content for continuously fast strand was introduced and obtained, Solute elements change the position of the strain curve. And cooling rate changes the position arid the shape of the strain curve. The comprehensive formula of the strain as functions of solute elements and cooling rate in brittle temperature range has been obtained by nonlinear fitting program.展开更多
A flexible technique of hot working of bars by axial feed rolling was introduced. The process deformation, strain field, stress field, and temperature fie M of the parts are analyzed by finite element method （ FEM）-...A flexible technique of hot working of bars by axial feed rolling was introduced. The process deformation, strain field, stress field, and temperature fie M of the parts are analyzed by finite element method （ FEM）-simulation software DEFORM-3D. The material flow rule and tool load have been investigated.展开更多
The shear responses of β-SiC are investigated using molecular dynamics simulation with the Tersoff interatomic potential. Results show a clear decreasing trend in critical stress,fracture strain and shear modulus as ...The shear responses of β-SiC are investigated using molecular dynamics simulation with the Tersoff interatomic potential. Results show a clear decreasing trend in critical stress,fracture strain and shear modulus as temperature increases. Above a critical temperature, β-SiC bulk just fractures after the elastic deformation. However, below the critical temperature, an interesting pattern in β-SiC bulk emerges due to the elongation of Si-C bonds before fracture. Additionally, the shear deformation of β-SiC at room temperature is found to be dependent on the strain rate. This study may shed light on the deformation mechanism dependent on temperature and strain rate.展开更多
In this Letter, an alternative solution is proposed and demonstrated for simultaneous measurement of axial strain and temperature. This sensor consists of two twisted points on a commercial single mode fiber introduce...In this Letter, an alternative solution is proposed and demonstrated for simultaneous measurement of axial strain and temperature. This sensor consists of two twisted points on a commercial single mode fiber introduced by flame-heated and rotation treatment. The fabrication process modifies the geometrical configuration and refractive index of the fiber. Different cladding modes are excited at the first twisted point, and part of them are coupled back to the fiber core at the second twisted point. Experimental results show distinct sensitivities of 34.9 pm/με with 49.23 pm/℃ and -36.19 pm/με with 62.99 pm/℃ for the two selected destructive interference wavelengths.展开更多
In order to research the temperature distribution and mechanical deformation of slab bulging during high speed continuous casting, mathematical models have been developed to analyze the thermal and mechanical behavior...In order to research the temperature distribution and mechanical deformation of slab bulging during high speed continuous casting, mathematical models have been developed to analyze the thermal and mechanical behavior of the slab. The thermal history of the slab has been predicted by a two-dimensional transient finite element heat transfer model, whose results serve as the input to the stress model. The stress model has been formulated for a two-dimensional longitudinal plane. In this case,the maximum tensile strain during the bulging process is located at the solidification fi＇ont just past the top of the upstream roll,which may contribute to crack formation. The maximum tensile stresses are located at the cold surface in the middle of the two back-up rolls ,just at the point of the maximum bulging. Stresses near the solidification fi＇ont are small because of the high temperatures which produce lower elastic modulus values. Finally,the effect of the casting speed on the bulging deformation is discussed.展开更多
In hot deformation, the flow stress curves of steels always present as two typical types: at relatively high temperature and low strain rate, the flow stress may first increase and then attain a steady value without r...In hot deformation, the flow stress curves of steels always present as two typical types: at relatively high temperature and low strain rate, the flow stress may first increase and then attain a steady value without reaching an obvious peak stress; in other situations, the flow stress decreases after reaching peak stress and then attains a steady value. A new phenomenological model,described by a sine-function equation, is proposed to define the relationship between flow stress and deformation parameters. A series of isothermal compressions for a carbon steel were carried out, as a case study, to obtain basic experimental data.Parameters of the new model were sequentially determined. The predicted results of the proposed model were compared with actual measured data. Good accuracy was found in the standard statistical parameters of correlation coefficient, root mean square error, and average absolute relative error with the values of 0.935, 7.137 MPa and 4.352%, respectively. Discussion of applications of different models in finite-element simulation demonstrated the benefit of the new model. When comparing the simulation results of three different deformation patterns with large strain, the new model showed 10%–20% lower predicted forming load than the original Arrhenius equation, and better applicability and reliability than modified Arrhenius equations.展开更多
Advanced sensing techniques are in big demand for applications in hypersonic wind tunnel harsh environments,such as aero(thermo)dynamics measurements,thermal protection of aircraft structures,air-breathing propulsion,...Advanced sensing techniques are in big demand for applications in hypersonic wind tunnel harsh environments,such as aero(thermo)dynamics measurements,thermal protection of aircraft structures,air-breathing propulsion,light-weighted and highstrength materials,etc.In comparison with traditional electromechanical or electronic sensors,the fiber optic sensors have relatively high potential to work in hypersonic wind tunnel,due to the capability of responding to a wide variety of parameters,high resolution,miniature size,high resistant to electromagnetic and radio frequency interferences,and multiplexing,and so on.This article has classified and summarized the research status and the representative achievement on the fiber optic sensing technologies,giving special attention to the summary of research status on the popular Fabry-Perot interferometric,fiber Bragg gratings and(quasi)distributed fiber optic sensors working in hypersonic wind tunnel environment,and discussed the current problems in special optical fiber sensing technologies.This article would be regarded as reference for the researchers in hypersonic wind tunnel experiment field.展开更多
In this paper,the possibility of the monatomic chain (MC) formation for ZnO material was studied by molecular dynamics (MD) simulation.The process of MC formation and the effects of temperature,strain rate and size we...In this paper,the possibility of the monatomic chain (MC) formation for ZnO material was studied by molecular dynamics (MD) simulation.The process of MC formation and the effects of temperature,strain rate and size were studied extensively.The tensile process can be divided to be five stages and the ZnO diatomic chain (DC) can be found.The MD results show that most atoms in MC came from the original surface of ZnO nanowires (NWs).Temperature and strain rate are two important factors affecting the process,and both high temperature and low strain rate in a certain range would be beneficial to the formation of DC.Moreover,the effects of strain rate and temperature could attribute to the Arrhenius model and the energy release mechanism.Furthermore,multi-shell structure was found for the samples under tensile strain and the layer-layer distance was about 3.Our studies based on density functional theory showed that the most stable structure of ZnO DC was confirmed to be linear,and the I-V curve was also got using ATK.展开更多
Optical fibre sensors based on Brillouin scattering have been vigorously studied in the context of structural health monitoring on account of their capacity for distributed strain and temperature measurements.However,...Optical fibre sensors based on Brillouin scattering have been vigorously studied in the context of structural health monitoring on account of their capacity for distributed strain and temperature measurements.However,real-time distributed strain measurement has been achieved only for two-end-access systems;such systems reduce the degree of freedom in embedding the sensors into structures,and furthermore render the measurement no longer feasible when extremely high loss or breakage occurs at a point along the sensing fibre.Here,we demonstrate real-time distributed measurement with an intrinsically one-end-access reflectometry configuration by using a correlation-domain technique.In this method,the Brillouin gain spectrum is obtained at high speed using a voltage-controlled oscillator,and the Brillouin frequency shift is converted into a phase delay of a synchronous sinusoidal waveform;the phase delay is subsequently converted into a voltage,which can be directly measured.When a single-point measurement is performed at an arbitrary position,a strain sampling rate of up to 100 kHz is experimentally verified by detecting locally applied dynamic strain at 1 kHz.When distributed measurements are performed at 100 points with 10 times averaging,a repetition rate of 100 Hz is verified by tracking a mechanical wave propagating along the fibre.Some drawbacks of this ultrahigh-speed configuration,including the reduced measurement accuracy,lowered spatial resolution and limited strain dynamic range,are also discussed.展开更多
基金This work is part of the crashworthiness R&D task of an on-going Canada-China-US Magnesium Front-End Research and Development(MFERD)project.The Canadian task is funded by the CCT&I and ASM-NGV programs,Govemment of Canada.
文摘The controlling plastic deformation mechanisms(i.e.slip or twinning)and the structural crash performance of Mg alloys are strongly influenced by loading mode,texture and microstructure.This paper summarizes the main results from an experimental program to assess these effects for commercial Mg alloy extrusions(AM30 and AZ31),sheet(AZ31),and high pressure die castings(HPDC,AM50 and AM60).Uniaxial tensile and compressive tests were performed over a wide range of strain rate and temperature(i.e.0.00075–2800 s^(−1) and 100℃ to−150℃)using conventional servo-hydraulic and high-strain-rate universal test machines and a split-Hopkinson-bar(SHB)apparatus.In primarily-slip-dominant deformation,the true stress–strain curves showed approximate power-law behavior,and the effects of strain rate and temperature on yield strength could be approximately described by constitutive equations linearly dependent on the rate parameter,Tln(5.3×10^(7)/ɛ˙)where T is test temperature in Kelvin andɛ˙is strain rate in s^(−1).In primarily-twin-dominant deformation,the effects of strain rate and temperature on yield and initial flow stress were negligible or small from quasi-static to 2800 s^(−1) owing to the athermal characteristics of mechanical twinning;the effects may become more pronounced with exhaustion of twinning and increasing proportion of slip.
基金supported by the Fundamental Research Funds for the Central Universities (No. 2011QNB05)the National Basic Research Program of China (No. 2007CB209400)+2 种基金the National Natural Science Foundation of China (Nos. 51074166 and 51104128)the Research Project for Ministry of Housing and Urban-Rural Development of China (No. 2011-K3-5)the Innovation Project of Graduate Students in Jiangsu Province (No. CX09B_108Z)
文摘The experimental tests for limestone specimens at 700 °C in uniaxial compression were carried out to inves- tigate the mechanical effects of loading rates on limestone by using a MTS810 rock mechanics servo- controlled testing system considering the loading rate as a variable. The mechanical properties of limestone such as the stress-strain curve, variable characteristics of peak strength and the modulus of elasticity of limestone were studied under the strain rates ranging from 1.1 10à5 to 1.1 10à1 sà1. (1) Sharp decreases were shown for the peak strength and elastic modulus of limestone from 1.1 10à5 to 1.1 10à4 sà1 at 700 °C as well as a downward trend was shown from 1.1 10à4 to 1.1 10à1 sà1 with the rise of the strain rate. (2) The peak strain increased from 1.1 10à5 to 1.1 10à4 sà1, however, there was no obvious changes shown for the peak strain of limestone from 1.1 10à4 to 1.1 10à1 sà1. These results can provide valuable references for the rock blasting effect and design of mine.
基金supported by the National Natural Science Foundation of China(Grant No.52068014)Key Research&Development Projects in the Guangxi Autonomous Region(Grant No.GUIKE AA20302006)Major Construction Program of the Science and Technological Innovation Base in the Guangxi Autonomous Region(Grant No.2018-242-G02).
文摘The strain-temperature cross-sensitivity problem easily occurs in the engineering strain monitoring of the self-sensing embedded with fiber Bragg grating(FBG)sensors.In this work,a theoretical investigation of the strain-temperature cross-sensitivity has been performed using the temperature reference grating method.To experimentally observe and theoretically verify the problem,the substrate materials,the preloading technique,and the FBG initial central wavelength were taken as main parameters.And a series of sensitivity coefficients calibration tests and temperature compensation tests have been designed and carried out.It was found that when the FBG sensors were embedded on different substrates,their coefficients of the temperature sensitivity were significantly changed.Besides,the larger the coefficients of thermal expansion(CTE)of substrates were,the higher the temperature sensitivity coefficients would be.On the other hand,the effect of the preloading technique and FBG initial wavelength was negligible on both the strain monitoring and temperature compensation.In the case of similar substrates,we did not observe any difference between temperature sensitivity coefficients of the temperature compensation FBG with one free end or two free ends.The curves of the force along with temperature were almost overlapped with minor differences(less than 1%)gained by FBG sensors and pressure sensors,which verified the accuracy of the temperature compensation method.We suggest that this work can provide efficient solutions to the strain-temperature cross-sensitivity for engineering strain monitoring with the self-sensing element embedded with FBG sensors.
基金supported by the National Natural Science Foundation of China (11372243, 11372243, 1152219)the International Science and Technology Cooperation Program of China (2013DFG02930)
文摘Pain sensation may appear under long-lasting mechanical stimulation. Although people have the experience that pain sensation generally decreases with time while the stimulation remains, the underlying mechanism remains elusive. We experimentally studied the thermal and strain rate- dependent viscoelastic behavior of skin in uniaxial stretch and numerically investigated the effects of temperature and strain rate on pain sensation. The results indicate that the viscosity of skin tissue decreases with increasing temperature and reducing strain rate, which subsequently decreases the discharge frequency of skin nociceptor and thus relieves the pain sensation. The results would contribute to the understanding of pain relief mechanism and optimizing for mechanical treatment.
基金National Natural Science Foundation of China(NSFC)(61635007,61425007,61377090,61575128)Guangdong Science and Technology Department(2014A030308007,2014B050504010,2015B010105007,2015A030313541)+1 种基金Science and Technology Innovation Commission of Shenzhen(GJHZ20150313093755757,JCYJ20160520163134575,JCYJ20160427104925452)Pearl River Scholar Fellowships
文摘A liquid modified photonic crystal fiber(PCF)integrated with an embedded directional coupler and multi-mode interferometer is fabricated by infiltrating three adjacent air holes of the innermost layer with standard 1.48 refractive index liquids.The refractive index of the filled liquid is higher than that of background silica,which can not only support the transmitting rod modes but also the"liquid modified core"modes propagating between the PCF core and the liquid rods.Hence,the light propagating in the liquid modified core can be efficiently coupled into the satellite waveguides under the phase-matching conditions,resulting in a dramatic decrease of the resonant wavelength intensity.Furthermore,there is a multi-mode interference produced by modified core modes and rod modes.Such a compact(~0.91 cm)device integrated with an embedded coupler and interferometer is demonstrated for high-sensitivity simultaneous temperature(~14.72 nm∕℃)and strain(~13.01 pm∕με)measurement.
基金supported by the National High Technology Research and Development Program of China(2014AA041504)the National Natural Science Foundation of China(51605161)
文摘During high speed machining in the field of manufacture,chip formation is a severe plastic deformation process including large strain,high strain rate and high temperature.And the strain rate in high speed cutting process can be achieved to 105 s^（-1）.30CrMnSiNi2Asteel is a kind of important high-strength low-alloy structural steel with wide application range.Obtaining the dynamic mechanical properties of30CrMnSiNi2Aunder the conditions of high strain rate and high temperature is necessary to construct the constitutive relation model for high speed machining.The dynamic compressive mechanical properties of30CrMnSiNi2Asteel were studied using split Hopkinson pressure bar（SHPB）tests at 30-700°C and3000-10000s^（-1）.The stress-strain curves of 30CrMnSiNi2Asteel at different temperatures and strain rates were investigated,and the strain hardening effect and temperature effect were discussed.Experimental results show that 30CrMnSiNi2Ahas obvious temperature sensitivity at 300°C.Moreover,the flow stress decreased significantly with the increase of temperature.The strain hardening effect of the material at high strain rate is not significant with the increase of strain.The strain rate hardening effect is obvious with increasing the temperature.According to the experimental results,the established Johnson-Cook（J-C）constitutive model of 30CrMnSiNi2Asteel could be used at high strain rate and high temperature.
文摘To study the effect of tempering temperature on strain hardening exponent and flow stress curve,one kind of 1000 MPa grade low carbon bainitic steel for construction machinery was designed,and the standard uniaxial tensile tests were conducted at room temperature.A new flow stress model,which could predict the flow behavior of the tested steels at different tempering temperatures more efficiently,was established.The relationship between mobile dislocation density and strain hardening exponent was discussed based on the dislocation-stress relation.Arrhenius equation and an inverse proportional function were adopted to describe the mobile dislocation,and two mathematical models were established to describe the relationship between tempering temperature and strain hardening exponent.Nonlinear regression analysis was applied to the Arrhenius type model,hence,the activation energy was determined to be 37.6kJ/mol.Moreover,the square of correlation coefficient was 0.985,which indicated a high reliability between the fitted curve and experimental data.By comparison with the Arrhenius type curve,the general trend of the inverse proportional fitting curve was coincided with the experimental data points except of some fitting errors.Thus,the Arrhenius type model can be adopted to predict the strain hardening exponent at different tempering temperatures.
基金This study is part of CanmetMATERIALS(CMAT)projects funded by the Magnesium Front End R&D(MFERD)program provided by Natural Resources Canada through the Program of Energy Research and Development and Transport Canada.
文摘A coarse-grained AM50 alloy was used as a model alloy for investigation of constitutive behaviour,Charpy toughness and effect of stress state on deformation and failure of cast Mg alloys.The results provide critical mechanical properties of a cast AM50 alloy for crashworthiness assessment and development of finite element simulation techniques.For cast Mg alloys,the effect of strain rate and temperature is larger on tensile strength than on compressive strength because twinning is more extensive in compression than in tension.The effect of strain rate on compressive strength is negligible because twinning activity of the cast Mg alloy is dominant.The load vs.deflection of Charpy specimens were measured for modelling,and the effect of loading rate and temperature on load of Charpy specimens is very small because part of the specimen is in compression.The equivalent strain to fracture of the cylindrical round notched tension specimen decreases with increasing stress triaxiality;though for the flat-grooved plane strain specimen,the equivalent fracture strain remains constant over the range of stress triaxiality investigated.Because the two different specimen geometries give rise to different Lode angle values,the test results show that the Lode angle parameter is an important parameter for deformation and fracture of Mg alloys.Finite element simulations of loading of the cylindrical notched-tension and Charpy specimens were carried out using a Lode-angle dependent von Mises model,and were found to provide a reasonable description of the load-displacement curves measured in the tests.For the flat-grooved plane strain specimens,the computations under-predicted the force-displacement response measured.
文摘A new approach utilizing effects of dispersion in the high-order-mode fibers （HOMFs） to effectively discriminate changes in environmental temperature and axial strain is proposed and experimentally demonstrated. Experimental characterization of a HOMF-based fiber modal interferometer with a sandwich fiber structure exhibits excellent agreements with numerical simulation results. A Fourier transform method of interferometry in the spatial frequency domain is adopted to distinguish mode coupling between different core-guided modes. Distinct phase sensitivities of multiple dispersion peaks are extracted by employing a novel phase demodulation scheme to realize dual-parameter sensing.
基金This work was supported in part by the National Natural Science Foundation of China(NSFC)(Grant Nos.61527819 and 61875146)in part by the Research Project Supported by Shanxi Province Youth Science and Technology Foundation(Grant No.201601D021069)+1 种基金in part by the Key Research and Development Program(High-Tech Field)of Shanxi Province(Grant Nos.201803D121064 and 201803D31044)in part by the Program for Sanjin Scholar,in part by the Transformation of Scientific and Technological Achievements Programs(TSTAP)of Higher Education Institutions in Shanxi,and in part by the Program for the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi.
文摘Chaotic Brillouin optical correlation domain analysis(BOCDA)has been proposed and experimentally demonstrated with the advantage of high spatial resolution.However,it faces the same issue of the temperature and strain cross-sensitivity.In this paper,the simultaneous measurement of temperature and strain can be preliminarily achieved by analyzing the two Brillouin frequencies of the chaotic laser in a large-effective-area fiber(LEAF).A temperature resolution of 1℃ and a strain resolution of 20μξ can be obtained with a spatial resolution of 3.9cm.The actual temperature and strain measurement errors are 0.37℃ and 10μξ,respectively,which are within the maximum measurement errors.
基金Item Sponsored by National Basic Research Program of China(2010CB630806-2)
文摘A micro-segregation model of solute elements in mushy zone with δ/γ transformation during solidification was established based on the regular hexagon transverse cross section of dendrite shape proposed by finite difference method under the non-equilibrium solidification condition. The model was used to calculate the non-equilibrium pseudo binary Fe-C phase diagram and the strain of steels induced by variation of temperature in brittle temperature range. On the basis of the phase diagram and the strain, the strain curve in brittle temperature range as a function of carbon content for continuously fast strand was introduced and obtained, Solute elements change the position of the strain curve. And cooling rate changes the position arid the shape of the strain curve. The comprehensive formula of the strain as functions of solute elements and cooling rate in brittle temperature range has been obtained by nonlinear fitting program.
基金the National Natural Science Foundation of China （Nos. 50205003 ,50675014）.
文摘A flexible technique of hot working of bars by axial feed rolling was introduced. The process deformation, strain field, stress field, and temperature fie M of the parts are analyzed by finite element method （ FEM）-simulation software DEFORM-3D. The material flow rule and tool load have been investigated.
基金supported by the National Natural Science Foundation of China(NSFC Grants No.11632014,11302161 and11302162)China Postdoctoral Science Foundation(Grant No.2013M542339)the Chang Jiang Scholar program
文摘The shear responses of β-SiC are investigated using molecular dynamics simulation with the Tersoff interatomic potential. Results show a clear decreasing trend in critical stress,fracture strain and shear modulus as temperature increases. Above a critical temperature, β-SiC bulk just fractures after the elastic deformation. However, below the critical temperature, an interesting pattern in β-SiC bulk emerges due to the elongation of Si-C bonds before fracture. Additionally, the shear deformation of β-SiC at room temperature is found to be dependent on the strain rate. This study may shed light on the deformation mechanism dependent on temperature and strain rate.
基金supported by the National Natural Science Foundation of China(Nos.61775070 and 61275083)the Fundamental Research Funds for the Central Universities(No.2017KFYXJJ032)
文摘In this Letter, an alternative solution is proposed and demonstrated for simultaneous measurement of axial strain and temperature. This sensor consists of two twisted points on a commercial single mode fiber introduced by flame-heated and rotation treatment. The fabrication process modifies the geometrical configuration and refractive index of the fiber. Different cladding modes are excited at the first twisted point, and part of them are coupled back to the fiber core at the second twisted point. Experimental results show distinct sensitivities of 34.9 pm/με with 49.23 pm/℃ and -36.19 pm/με with 62.99 pm/℃ for the two selected destructive interference wavelengths.
文摘In order to research the temperature distribution and mechanical deformation of slab bulging during high speed continuous casting, mathematical models have been developed to analyze the thermal and mechanical behavior of the slab. The thermal history of the slab has been predicted by a two-dimensional transient finite element heat transfer model, whose results serve as the input to the stress model. The stress model has been formulated for a two-dimensional longitudinal plane. In this case,the maximum tensile strain during the bulging process is located at the solidification fi＇ont just past the top of the upstream roll,which may contribute to crack formation. The maximum tensile stresses are located at the cold surface in the middle of the two back-up rolls ,just at the point of the maximum bulging. Stresses near the solidification fi＇ont are small because of the high temperatures which produce lower elastic modulus values. Finally,the effect of the casting speed on the bulging deformation is discussed.
基金supported by the National Natural Science Foundation of China(Grant No.51475294)
文摘In hot deformation, the flow stress curves of steels always present as two typical types: at relatively high temperature and low strain rate, the flow stress may first increase and then attain a steady value without reaching an obvious peak stress; in other situations, the flow stress decreases after reaching peak stress and then attains a steady value. A new phenomenological model,described by a sine-function equation, is proposed to define the relationship between flow stress and deformation parameters. A series of isothermal compressions for a carbon steel were carried out, as a case study, to obtain basic experimental data.Parameters of the new model were sequentially determined. The predicted results of the proposed model were compared with actual measured data. Good accuracy was found in the standard statistical parameters of correlation coefficient, root mean square error, and average absolute relative error with the values of 0.935, 7.137 MPa and 4.352%, respectively. Discussion of applications of different models in finite-element simulation demonstrated the benefit of the new model. When comparing the simulation results of three different deformation patterns with large strain, the new model showed 10%–20% lower predicted forming load than the original Arrhenius equation, and better applicability and reliability than modified Arrhenius equations.
基金the National Natural Science Foundation of China(NSFC)(Project Nr.:2012YQ25002,11802329).
文摘Advanced sensing techniques are in big demand for applications in hypersonic wind tunnel harsh environments,such as aero(thermo)dynamics measurements,thermal protection of aircraft structures,air-breathing propulsion,light-weighted and highstrength materials,etc.In comparison with traditional electromechanical or electronic sensors,the fiber optic sensors have relatively high potential to work in hypersonic wind tunnel,due to the capability of responding to a wide variety of parameters,high resolution,miniature size,high resistant to electromagnetic and radio frequency interferences,and multiplexing,and so on.This article has classified and summarized the research status and the representative achievement on the fiber optic sensing technologies,giving special attention to the summary of research status on the popular Fabry-Perot interferometric,fiber Bragg gratings and(quasi)distributed fiber optic sensors working in hypersonic wind tunnel environment,and discussed the current problems in special optical fiber sensing technologies.This article would be regarded as reference for the researchers in hypersonic wind tunnel experiment field.
基金supported by the National Natural Science Foundation of China (Grant No.60936001)
文摘In this paper,the possibility of the monatomic chain (MC) formation for ZnO material was studied by molecular dynamics (MD) simulation.The process of MC formation and the effects of temperature,strain rate and size were studied extensively.The tensile process can be divided to be five stages and the ZnO diatomic chain (DC) can be found.The MD results show that most atoms in MC came from the original surface of ZnO nanowires (NWs).Temperature and strain rate are two important factors affecting the process,and both high temperature and low strain rate in a certain range would be beneficial to the formation of DC.Moreover,the effects of strain rate and temperature could attribute to the Arrhenius model and the energy release mechanism.Furthermore,multi-shell structure was found for the samples under tensile strain and the layer-layer distance was about 3.Our studies based on density functional theory showed that the most stable structure of ZnO DC was confirmed to be linear,and the I-V curve was also got using ATK.
基金supported by JSPS KAKENHI Grant Numbers 25709032,26630180 and 25007652by research grants from the Iwatani Naoji FoundationSCAT Foundation and the Konica Minolta Science and Technology Foundation.
文摘Optical fibre sensors based on Brillouin scattering have been vigorously studied in the context of structural health monitoring on account of their capacity for distributed strain and temperature measurements.However,real-time distributed strain measurement has been achieved only for two-end-access systems;such systems reduce the degree of freedom in embedding the sensors into structures,and furthermore render the measurement no longer feasible when extremely high loss or breakage occurs at a point along the sensing fibre.Here,we demonstrate real-time distributed measurement with an intrinsically one-end-access reflectometry configuration by using a correlation-domain technique.In this method,the Brillouin gain spectrum is obtained at high speed using a voltage-controlled oscillator,and the Brillouin frequency shift is converted into a phase delay of a synchronous sinusoidal waveform;the phase delay is subsequently converted into a voltage,which can be directly measured.When a single-point measurement is performed at an arbitrary position,a strain sampling rate of up to 100 kHz is experimentally verified by detecting locally applied dynamic strain at 1 kHz.When distributed measurements are performed at 100 points with 10 times averaging,a repetition rate of 100 Hz is verified by tracking a mechanical wave propagating along the fibre.Some drawbacks of this ultrahigh-speed configuration,including the reduced measurement accuracy,lowered spatial resolution and limited strain dynamic range,are also discussed.
