In situ strain photoluminescence （PL） and Raman spectroscopy have been employed to exploit the evolutions of the electronic band structure and lattice vibrational responses of chemical vapor deposition （CVD）-grown...In situ strain photoluminescence （PL） and Raman spectroscopy have been employed to exploit the evolutions of the electronic band structure and lattice vibrational responses of chemical vapor deposition （CVD）-grown monolayer tungsten disulphide （WS2） under uniaxial tensile strain. Observable broadening and appearance of an extra small feature at the longer-wavelength side shoulder of the PL peak occur under 2.5% strain, which could indicate the direct-indirect bandgap transition and is further confirmed by our density-functional-theory calculations. As the strain increases further, the spectral weight of the indirect transition gradually increases. Over the entire strain range, with the increase of the strain, the light emissions corresponding to each optical transition, such as the direct bandgap transition （K-K） and indirect bandgap transition （F-K, ≥2.5%）, exhibit a monotonous linear redshift. In addition, the binding energy of the indirect transition is found to be larger than that of the direct transition, and the slight lowering of the trion dissociation energy with increasing strain is observed. The strain was used to modulate not only the electronic band structure but also the lattice vibrations. The softening and splitting of the in-plane E＇ mode is observed under uniaxial tensile strain, and polarization-dependent Raman spectroscopy confirms the observed zigzag-oriented edge of WS2 grown by CVD in previous studies. These findings enrich our understanding of the strained states of monolayer transition-metal dichalcogenide （TMD） materials and lay a foundation for developing applications exploiting their strain-dependent optical properties, including the strain detection and light-emission modulation of such emerging two-dimensional TMDs.展开更多
Molecular dynamics simulation was employed to study the tensile behavior of single crystal titanium nanowires（NWs）with[112^-0],[1^-100] and[0001]orientations at different strain rates from 10^8s^-1 to 10^11s^-1.When...Molecular dynamics simulation was employed to study the tensile behavior of single crystal titanium nanowires（NWs）with[112^-0],[1^-100] and[0001]orientations at different strain rates from 10^8s^-1 to 10^11s^-1.When strain rates are above 10^10s^-1,the state transformation from HCP structure to amorphous state leads to super plasticity of Ti NWs,which is similar to FCC NWs.When strain rates are below 10^10s^-1,deformation mechanisms of Ti NWs show strong dependence on orientation.For [112^-0] orientated NW.{101^-1} compression twins（CTs）and the frequently activated transformation between CTs and deformation faults lead to higher plasticity than the other two orientated NWs.Besides,tensile deformation process along [112^-0] orientation is insensitive to strain rate.For [1^-100] orientated NW,prismaticslip is the main deformation mode at 10^8s^-1.As the strain rate increases,more types of dislocations are activated during plastic deformation process.For[0001]orientated NW,{101^-2} extension twinning is the main deformation mechanism,inducing the yield stress of [0001] orientated NW,which has the highest strain rate sensitivity.The number of initial nucleated twins increases while the saturation twin volume fraction decreases nonlinearly with increasing strain rate.展开更多
The thermal simulation compression tests of near-β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe were per-formed within the range of deformation temperatures of 710-860 ℃ and strain rates of 0.001-1 s^(-1).Based on electron ...The thermal simulation compression tests of near-β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe were per-formed within the range of deformation temperatures of 710-860 ℃ and strain rates of 0.001-1 s^(-1).Based on electron backscatter diffraction(EBSD)characterization and analysis technology,the inter-action between dynamic phase transformation(DPT)of β-to-α and dynamic recrystallization(DRX)under thermal-mechanical coupling is deeply and systematically explored.We clarify the effects of temperatures and strain rates on the orientation relationship during dynamic precipitation of α-phase within β grain interiors possessing special orientation.The results show that the intragranular α-phase precipitated on the subgrain boundaries near {001}β with a high degree of dynamic recovery(DRV)deviates more from Burgers Orientation Relationship(BOR)than the α-phase that precipitates near{111}βas temperature increases.The proportion of α-phase precipitated by strain-induced on β recrys-tallized equiaxed grains for the deviating angle from BOR(θBoR)in the range of 20°-30° increases to 40%with the increase of strain rates below 800 ℃.In addition,the α-phase is dynamically precipitated on the grain boundaries with {110}β orientation,which undergoes continuous dynamic recrystallization(CDRX),exhibiting epitaxial recrystallization,namely {110}β//{0001 }α.Furthermore,the morphology of grain boundaries α phase(αGBs)precipitated by strain-induced phase transformation(SIPT)on specific types of β grain boundaries(βGBs),as well as the crystallographic orientation relationship and variant selection effect between adjacent α-variant within β grains are elucidated.The orientation relationships between α variants in {111}β grain are related with each other by 50°-60°/<-12-10>and 60°-70°/<-48-43>rotation.The"necklace"αGBs of recrystallization exhibit mainly the rotation of 50°-70° around the<2-310>zone axis,while the adjacent α-variant in the grain interiors is mainly 60° or 90°/<12-30>.In summary,the study h展开更多
New natural rubber(NR)/nitrile butadiene rubber(NBR)/hindered phenol(AO-80)composites with high-damping properties were prepared in this study.The morpholo-gical,structural,and mechanical properties were characterized...New natural rubber(NR)/nitrile butadiene rubber(NBR)/hindered phenol(AO-80)composites with high-damping properties were prepared in this study.The morpholo-gical,structural,and mechanical properties were characterized by atomic force micro-scopy(AFM),polarized Fourier transform infrared spectrometer(FTIR),dynamic mechanical thermal analyzer(DMTA),and a tensile tester.Each composite consisted of two phases:the NR phase and the NBR/AO-80 phase.There was partial compat-ibility between the NR phase and the NBR/AO-80 phase,and the NR/NBR/AO-80(50/50/20)composite exhibited a co-continuous morphology.Strain-induced crystal-lization occurred in the NR phase at strains higher than 200%,and strain-induced orientation appeared in the NBR/AO-80 phase with the increase of strain from 100%to 500%.The composites had a special stress–strain behavior and mechanical properties because of the simultaneous strain-induced orientation and strain-induced crystalliza-tion.In the working temperature range of a seismic isolation bearing,the composites(especially the NR/NBR/AO-80(50/50/20)composite)presented a high loss factor,high area of loss peak(TA),and high hysteresis energy.Therefore,the NR/NBR/AO-80 rubber composites are expected to have important application as a high-perfor-mance damping material for rubber bearing.展开更多
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
Low cycle fatigue tests were conducted on the single crystal nickel-based superalloy, DD6, with different crystallographic orientations （i.e., [001], [011], and [111]） and strain dwell types （i.e, tensile, compress...Low cycle fatigue tests were conducted on the single crystal nickel-based superalloy, DD6, with different crystallographic orientations （i.e., [001], [011], and [111]） and strain dwell types （i.e, tensile, compressive, and balanced types） at a certain high temperature. Given the material anisotropy and mean stress, both orientation factor and stress range were introduced to the Smith, Watson, and Topper （SWT） stress model to predict the fatigue life. Experimental results indicated that the fatigue properties of DD6 depend on both crystallographic orientation and loading types. The fatigue life of the tensile, compressive, and balanced strain dwell tests are shorter than those of continuous cycling tests without strain dwell because of the important creep effect. The predicted results of the proposed modified SWT stress method agree well with the experimental data.展开更多
The correlation between crystal rotation and redundant shear strain in rolled single crystals was investigated by using the crystal plasticity finite element(CPFE) model in this paper. The deformation in aluminium sin...The correlation between crystal rotation and redundant shear strain in rolled single crystals was investigated by using the crystal plasticity finite element(CPFE) model in this paper. The deformation in aluminium single crystals of four representative orientations(rotated-Cube, Goss, Copper, and Brass) after rolling and plain strain compression was simulated, and the predictions have been validated by the experimental observations. In the rotated-Cube and Goss, the redundant shear strain and crystal rotation were in the same pattern, alternating along the thickness, while the relation between them was not obvious for the Copper and Brass due to their asymmetrical distributions of activated slip systems. The relations between slip system activation, crystal rotation, and shear strain were investigated based on the CPFE model, and the correlation between shear strain and crystal rotation has been built.展开更多
The cell alignment in a smooth muscle tissue plays a significant role in determining its mechanical proper-ties. The off-axis cell orientation 'θ” not only effects the shortening strain but also modifies the she...The cell alignment in a smooth muscle tissue plays a significant role in determining its mechanical proper-ties. The off-axis cell orientation 'θ” not only effects the shortening strain but also modifies the shear stress relationship significantly. Both experiments and finite element analysis were carried out on a tracheal smooth muscle strip to study how the cell alignment in smooth muscle affects the shear stiffness and shear stresses as well as deformation. A simple model for shear stiffness is derived using the data from experiments. Shear stiffness results obtained from the model indicate that the muscle shear stiff-ness values increase non-linearly with strain and with higher off-axis alignment of cells. Results of deforma-tion and shear stresses obtained from finite element analsysis indicate that the maximum shear stress values of tracheal smooth muscle tissue at 45% of strain are 2.5 times the corresponding values at 20% of strain for all three off-axis cell orientation values θ = 15?, 30? and 45?.展开更多
Based on Fermi＇s golden rule and the theory of Boltzmann collision term approximation, the hole scattering mechanism related to stress and orientation in Si-based strained materials was studied in-depth. The results ...Based on Fermi＇s golden rule and the theory of Boltzmann collision term approximation, the hole scattering mechanism related to stress and orientation in Si-based strained materials was studied in-depth. The results show that： （1） the total hole scattering rates in Si-based strained materials decrease obviously under strain; （2） the turn is Si/（111）Sil-xGex 〉 Si/（101）Si1-xGex 〉 Sil-xGex/（1111）Si 〉 Sil-xGex/（101）Si 〉 Si/（001）Sil-xGex 〉 Sil-xGex/（001）Si when Ge fraction is about 0.2; （3） the decreasing total hole scattering rates of in strained materials with the increasing stress is mainly caused the decreasing acoustic phonon scattering rate under strain. The theoretical conclusions obtained could provide important references for researching the hole mobility and the understanding of Si-based materials or other physical strained materials.展开更多
基金This work is supported by the Singapore National Research Foundation NRF RF Award No. NRFRF2010- 07, MOE Tier 2 MOE2012-T2-2-049, A＇Star SERC PSF grant No. 1321202101, and MOE Tier 1 MOE2013- T1-2-235. W. Huang acknowledges the support of the National Basic Research Program of China （973 Program） （No. 2015CB932200）, the National Natural Science Foundation of China （NSFC） （Grant Nos. 21144004, 20974046, 21101095, 21003076, 20774043, 51173081, 50428303, 61136003, and 50428303）, the Ministry of Education of China （No. IRT1148）, the NSF of Jiangsu Province （Grant Nos. SBK201122680, 11KJB510017, BK2008053, 11KJB510017, BK2009025, 10KJB510013, and BZ2010043）, and NUPT （Nos. NY210030 and NY211022）. J. R Wang is grateful for the NSFC （No. 11474164）, NSF of Jiangsu province （No. BK20131413）, and the Jiangsu Specially-Appointed Professor program. Y. L. Wang thanks Luqing Wang, Dr. Xiaolong Zou, and Dr. Alex Kutana for the constructive discussion.
文摘In situ strain photoluminescence （PL） and Raman spectroscopy have been employed to exploit the evolutions of the electronic band structure and lattice vibrational responses of chemical vapor deposition （CVD）-grown monolayer tungsten disulphide （WS2） under uniaxial tensile strain. Observable broadening and appearance of an extra small feature at the longer-wavelength side shoulder of the PL peak occur under 2.5% strain, which could indicate the direct-indirect bandgap transition and is further confirmed by our density-functional-theory calculations. As the strain increases further, the spectral weight of the indirect transition gradually increases. Over the entire strain range, with the increase of the strain, the light emissions corresponding to each optical transition, such as the direct bandgap transition （K-K） and indirect bandgap transition （F-K, ≥2.5%）, exhibit a monotonous linear redshift. In addition, the binding energy of the indirect transition is found to be larger than that of the direct transition, and the slight lowering of the trion dissociation energy with increasing strain is observed. The strain was used to modulate not only the electronic band structure but also the lattice vibrations. The softening and splitting of the in-plane E＇ mode is observed under uniaxial tensile strain, and polarization-dependent Raman spectroscopy confirms the observed zigzag-oriented edge of WS2 grown by CVD in previous studies. These findings enrich our understanding of the strained states of monolayer transition-metal dichalcogenide （TMD） materials and lay a foundation for developing applications exploiting their strain-dependent optical properties, including the strain detection and light-emission modulation of such emerging two-dimensional TMDs.
基金the financial supports of the National Natural Science Foundation of China (Nos.51475223,51675260)the Graduate Student Scientific Innovative Project of Jiangsu Province (No.KYLX16 0595)
文摘Molecular dynamics simulation was employed to study the tensile behavior of single crystal titanium nanowires（NWs）with[112^-0],[1^-100] and[0001]orientations at different strain rates from 10^8s^-1 to 10^11s^-1.When strain rates are above 10^10s^-1,the state transformation from HCP structure to amorphous state leads to super plasticity of Ti NWs,which is similar to FCC NWs.When strain rates are below 10^10s^-1,deformation mechanisms of Ti NWs show strong dependence on orientation.For [112^-0] orientated NW.{101^-1} compression twins（CTs）and the frequently activated transformation between CTs and deformation faults lead to higher plasticity than the other two orientated NWs.Besides,tensile deformation process along [112^-0] orientation is insensitive to strain rate.For [1^-100] orientated NW,prismaticslip is the main deformation mode at 10^8s^-1.As the strain rate increases,more types of dislocations are activated during plastic deformation process.For[0001]orientated NW,{101^-2} extension twinning is the main deformation mechanism,inducing the yield stress of [0001] orientated NW,which has the highest strain rate sensitivity.The number of initial nucleated twins increases while the saturation twin volume fraction decreases nonlinearly with increasing strain rate.
文摘The thermal simulation compression tests of near-β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe were per-formed within the range of deformation temperatures of 710-860 ℃ and strain rates of 0.001-1 s^(-1).Based on electron backscatter diffraction(EBSD)characterization and analysis technology,the inter-action between dynamic phase transformation(DPT)of β-to-α and dynamic recrystallization(DRX)under thermal-mechanical coupling is deeply and systematically explored.We clarify the effects of temperatures and strain rates on the orientation relationship during dynamic precipitation of α-phase within β grain interiors possessing special orientation.The results show that the intragranular α-phase precipitated on the subgrain boundaries near {001}β with a high degree of dynamic recovery(DRV)deviates more from Burgers Orientation Relationship(BOR)than the α-phase that precipitates near{111}βas temperature increases.The proportion of α-phase precipitated by strain-induced on β recrys-tallized equiaxed grains for the deviating angle from BOR(θBoR)in the range of 20°-30° increases to 40%with the increase of strain rates below 800 ℃.In addition,the α-phase is dynamically precipitated on the grain boundaries with {110}β orientation,which undergoes continuous dynamic recrystallization(CDRX),exhibiting epitaxial recrystallization,namely {110}β//{0001 }α.Furthermore,the morphology of grain boundaries α phase(αGBs)precipitated by strain-induced phase transformation(SIPT)on specific types of β grain boundaries(βGBs),as well as the crystallographic orientation relationship and variant selection effect between adjacent α-variant within β grains are elucidated.The orientation relationships between α variants in {111}β grain are related with each other by 50°-60°/<-12-10>and 60°-70°/<-48-43>rotation.The"necklace"αGBs of recrystallization exhibit mainly the rotation of 50°-70° around the<2-310>zone axis,while the adjacent α-variant in the grain interiors is mainly 60° or 90°/<12-30>.In summary,the study h
基金This work was supported by the National Natural Science Foundation of China[grant number 51320105012],[grant number 51221002],[grant number 51103006],[grant number 51373010].
文摘New natural rubber(NR)/nitrile butadiene rubber(NBR)/hindered phenol(AO-80)composites with high-damping properties were prepared in this study.The morpholo-gical,structural,and mechanical properties were characterized by atomic force micro-scopy(AFM),polarized Fourier transform infrared spectrometer(FTIR),dynamic mechanical thermal analyzer(DMTA),and a tensile tester.Each composite consisted of two phases:the NR phase and the NBR/AO-80 phase.There was partial compat-ibility between the NR phase and the NBR/AO-80 phase,and the NR/NBR/AO-80(50/50/20)composite exhibited a co-continuous morphology.Strain-induced crystal-lization occurred in the NR phase at strains higher than 200%,and strain-induced orientation appeared in the NBR/AO-80 phase with the increase of strain from 100%to 500%.The composites had a special stress–strain behavior and mechanical properties because of the simultaneous strain-induced orientation and strain-induced crystalliza-tion.In the working temperature range of a seismic isolation bearing,the composites(especially the NR/NBR/AO-80(50/50/20)composite)presented a high loss factor,high area of loss peak(TA),and high hysteresis energy.Therefore,the NR/NBR/AO-80 rubber composites are expected to have important application as a high-perfor-mance damping material for rubber bearing.
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The financial support for this work from the National Natural Science Foundation of China （Grant No. 51341001） is appreciated.
文摘Low cycle fatigue tests were conducted on the single crystal nickel-based superalloy, DD6, with different crystallographic orientations （i.e., [001], [011], and [111]） and strain dwell types （i.e, tensile, compressive, and balanced types） at a certain high temperature. Given the material anisotropy and mean stress, both orientation factor and stress range were introduced to the Smith, Watson, and Topper （SWT） stress model to predict the fatigue life. Experimental results indicated that the fatigue properties of DD6 depend on both crystallographic orientation and loading types. The fatigue life of the tensile, compressive, and balanced strain dwell tests are shorter than those of continuous cycling tests without strain dwell because of the important creep effect. The predicted results of the proposed modified SWT stress method agree well with the experimental data.
基金financially supported by the National Natural Science Foundation of China (12174237, 51901118, 51871137, and 52171183)the 1331 Engineering of Shanxi Province, the Research Project Supported by Shanxi Scholarship Council of China (2021-093)+1 种基金the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi (2020L0237)the Project funded by China Postdoctoral Science Foundation (2023M730422)。
文摘The correlation between crystal rotation and redundant shear strain in rolled single crystals was investigated by using the crystal plasticity finite element(CPFE) model in this paper. The deformation in aluminium single crystals of four representative orientations(rotated-Cube, Goss, Copper, and Brass) after rolling and plain strain compression was simulated, and the predictions have been validated by the experimental observations. In the rotated-Cube and Goss, the redundant shear strain and crystal rotation were in the same pattern, alternating along the thickness, while the relation between them was not obvious for the Copper and Brass due to their asymmetrical distributions of activated slip systems. The relations between slip system activation, crystal rotation, and shear strain were investigated based on the CPFE model, and the correlation between shear strain and crystal rotation has been built.
文摘The cell alignment in a smooth muscle tissue plays a significant role in determining its mechanical proper-ties. The off-axis cell orientation 'θ” not only effects the shortening strain but also modifies the shear stress relationship significantly. Both experiments and finite element analysis were carried out on a tracheal smooth muscle strip to study how the cell alignment in smooth muscle affects the shear stiffness and shear stresses as well as deformation. A simple model for shear stiffness is derived using the data from experiments. Shear stiffness results obtained from the model indicate that the muscle shear stiff-ness values increase non-linearly with strain and with higher off-axis alignment of cells. Results of deforma-tion and shear stresses obtained from finite element analsysis indicate that the maximum shear stress values of tracheal smooth muscle tissue at 45% of strain are 2.5 times the corresponding values at 20% of strain for all three off-axis cell orientation values θ = 15?, 30? and 45?.
文摘Based on Fermi＇s golden rule and the theory of Boltzmann collision term approximation, the hole scattering mechanism related to stress and orientation in Si-based strained materials was studied in-depth. The results show that： （1） the total hole scattering rates in Si-based strained materials decrease obviously under strain; （2） the turn is Si/（111）Sil-xGex 〉 Si/（101）Si1-xGex 〉 Sil-xGex/（1111）Si 〉 Sil-xGex/（101）Si 〉 Si/（001）Sil-xGex 〉 Sil-xGex/（001）Si when Ge fraction is about 0.2; （3） the decreasing total hole scattering rates of in strained materials with the increasing stress is mainly caused the decreasing acoustic phonon scattering rate under strain. The theoretical conclusions obtained could provide important references for researching the hole mobility and the understanding of Si-based materials or other physical strained materials.
