High-performance fiber fabrics and composites experienced transverse compression deformation at ultrahigh strain rates near the impact point when subjected to high-velocity impacts,which significantly affected their b...High-performance fiber fabrics and composites experienced transverse compression deformation at ultrahigh strain rates near the impact point when subjected to high-velocity impacts,which significantly affected their ballistic limits.In this paper,a fiber-scale experimental method for characterizing ultrahigh strain-rate transverse compression behavior was proposed.To begin with,in order to measure the extremely low stress and strain in small specimens,the conventional Hopkinson bar was reduced to the hundred-micron scale,thereby achieving wave impedance matching with single fibers.In addition,tangential and normal laser Doppler velocimetry(LDV)methods were employed to realize non-contact,high-precision,and high-speed axial velocity measurements of micron-scale incident and transmission bars,respectively.Meanwhile,a microscopic observation system was used to facilitate the installation of miniature fiber samples.The experimental setup and procedures were introduced,and the system accuracy was verified through sample-free loading tests based on one-dimensional stress wave propagation theory.Dynamic compression experiments on Graphene-UHMWPE fibers were carried out,followed by post-compression microstructural characterization via scanning electron microscopy(SEM).Results demonstrated that successful mechanical characterization was achieved at strain rates exceeding 105,an order of magnitude higher than the previously reported maximum rates.Furthermore,during the loading process,the fibers underwent uniform compression deformation while exhibiting pronounced strain-rate effects.This method offers a novel approach for dynamic mechanical characterization of microscale single fibers,enabling the development of comprehensive strain-ratedependent material models to guide the design of advanced composites and high-performance fibers.展开更多
Recent advances in additive manufacturing have enabled the construction of metallic lattice structures with tailored mechanical and functional properties.One potential application of metallic lattice struc-tures is in...Recent advances in additive manufacturing have enabled the construction of metallic lattice structures with tailored mechanical and functional properties.One potential application of metallic lattice struc-tures is in the impact load mitigation where an external kinetic energy is absorbed by the deformation/crushing of lattice cells.This has motivated a growing number of experimental and numerical studies,recently,on the crushing behavior of additively produced lattice structures.The present study overviews the dynamic and quasi-static crushing behavior of additively produced Ti64,316L,and AlSiMg alloy lattice structures.The first part of the study summarizes the main features of two most commonly used additive processing techniques for lattice structures,namely selective-laser-melt(SLM)and electro-beam-melt(EBM),along with a description of commonly observed process induced defects.In the second part,the deformation and strain rate sensitivities of the selected alloy lattices are outlined together with the most widely used dynamic test methods,followed by a part on the observed micro-structures of the SLM and EBM-processed Ti64,316L and AlSiMg alloys.Finally,the experimental and numerical studies on the quasi-static and dynamic compression behavior of the additively processed Ti64,316L,and AlSiMg alloy lattices are reviewed.The results of the experimental and numerical studies of the dynamic properties of various types of lattices,including graded,non-uniform strut size,hollow,non-uniform cell size,and bio-inspired,were tabulated together with the used dynamic testing methods.The dynamic tests have been noted to be mostly conducted in compression Split Hopkinson Pressure Bar(SHPB)or Taylor-and direct-impact tests using the SHPB set-up,in all of which relatively small-size test specimens were tested.The test specimen size effect on the compression behavior of the lattices was further emphasized.It has also been shown that the lattices of Ti64 and AlSiMg alloys are relatively brittle as compared with the lattices of 316L alloy.Finally,the challenges associated with modelling lattice structures were explained and the micro tension tests and multi-scale modeling techniques combining microstructural characteristics with macroscopic lattice dynamics were recommended to improve the accuracy of the numerical simulations of the dynamic compression deformations of metallic lattice structures.展开更多
The slow kinetics of the cathode CO_(2) reduction reaction and the decomposition reaction of Li2CO3,a widebandwidth insulating product,lead to difficult CO_(2) capture and high charging potential in Li-CO_(2) batterie...The slow kinetics of the cathode CO_(2) reduction reaction and the decomposition reaction of Li2CO3,a widebandwidth insulating product,lead to difficult CO_(2) capture and high charging potential in Li-CO_(2) batteries.To improve the reaction kinetics and decrease the reaction overpotential,we synthesized mesoporous Pt nanosheets with high tensile strain.The presence of many unsaturated coordinated Pt atoms around the pores gives rise to tensile strain in the mesoporous Pt nanosheets.This tensile strain plays a key role in regulating the interactions between the catalytic surface of Pt and the adsorbed intermediates.The two-dimensional structure provides more active sites on the surface for the catalytic reactions.These superiorities enable a low overpotential of 0.36 V at a cutoff capacity of 100μAh·cm^(−2) at a current density of 10μA·cm^(−2) over more than 2000 h.This study opens new possibilities for the rational design of metal-based materials with strain engineering for electrochemical energy storage.展开更多
Quasi-static and high strain rate compressive experiments on vinyl ester casting were carried out by means of MTS (Material Test System) and Hopkinson bar. The behaviors of the compressed unstable and fracture of the ...Quasi-static and high strain rate compressive experiments on vinyl ester casting were carried out by means of MTS (Material Test System) and Hopkinson bar. The behaviors of the compressed unstable and fracture of the resin casting at different strain rates were investigated.The results indicate that the response behavior of the resin casting is controlled by different mechanisms at different strain rate, and some mechanical properties of vinyl ester casting are rate-dependent: the casting are destroyed in toughness model under strain rate 3.3×10 -4～6.6×10 -3/s, while the casting are destroyed in brittleness model under strain rate 950～5800/s. The yield stress, yield strain energy density are all increased with the increasing strain rates at quasi-static as well as at high strain rates. What is interesting is that the yield strain decreased with the strain rates increasing at quasi-static while increased at high strain rates. It is considered that the casting occurred forcing high elastic deformation at high strain rates. The damage of the specimens is mainly controlled by axial stress before unstable deformation, while mainly controlled by shear stress after unstable deformation, and then developed to fracture finally. This progress is rate-dependent: the development of the cracks inside the castings increased with the strain rate increasing.展开更多
Citrus tristeza virus （CTV）, the most devastating viral pathogen in citrus, causes tremendous economic losses to citrus industry worldwide. The CTV isolates exhibit variable pathogenicities on their hosts indicating...Citrus tristeza virus （CTV）, the most devastating viral pathogen in citrus, causes tremendous economic losses to citrus industry worldwide. The CTV isolates exhibit variable pathogenicities on their hosts indicating a mixed population of the CTV in nature. Several fragments within the CTV genome have been used for studying the genetic diversity of the CTV, however, the best region for rapid the CTV strain differentiation is still absent at present. In present study, a systemic analysis was carried out to evaluate the best region within the CTV genome for rapid CTV strain differentiation. Results of our study showed that the major coat protein （CP） coding region was the best region for this purpose. Using pair-wise distance frequency distribution plot, a reasonable genetic distance cut-off value was set for the CTV CP gene for the CTV strain differentiation. Using this criterion, eight CTV strains, including seven well characterized and a new strain, were successfully differentiated using 537 CTV isolates reported from 38 countries. The global strain distribution pattern was then determined and discussed. Our results also provided a new insight into the evolution and spreading of the virus, as well as the information for developing proper disease management strategy.展开更多
On the basis of the GPS data obtained from repeated measurements carried out in 2004 and 2007,the horizontal principal strain of the Chinese mainland is calculated,which shows that the direction of principal compressi...On the basis of the GPS data obtained from repeated measurements carried out in 2004 and 2007,the horizontal principal strain of the Chinese mainland is calculated,which shows that the direction of principal compressive strain axis of each subplate is basically consistent with the P-axis of focal mechanism solution and the principal compressive stress axis acquired by geological method.It indicates that the crustal tectonic stress field is relatively stable in regions in a long time.The principal compressive stress axes of Qinghai-Tibet and Xinjiang subplates in the western part of Chinese mainland direct to NS and NNE-SSW,which are controlled by the force from the col-lision of the Eurasia Plate and India Plate.The principal compressive strain axes of Heilongjiang and North China subplates in the eastern part direct to ENE-WSW,which shows that they are subject to the force from the collision and underthrust of the Eurasia Plate to the North America and Pacific plates.At the same time,they are also af-fected by the lateral force from Qinghai-Tibet and Xinjiang subplates.The principal compressive strain axis of South China plate is WNW-ESE,which reflects that it is affected by the force from the collision of Philippine Sea Plate and Eurasia Plate and it is also subject to the lateral force from Qinghai-Tibet subplate.It is apparent from the comparison between the principal compressive strain axes in the periods of 2004～2007 and 2001～2004 that the acting directions of principal compressive stress of subplates in both periods are basically consistent.However,there is certain difference between their directional concentrations of principal compressive stress axes.The sur-face strain rates of different tectonic units in both periods indicate that the events predominating by compressive variation decrease,while the events predominating by tensile change increase.展开更多
In order to study the influences of confining pressure and strain rate on the mechanical properties of the Nitrate Ester Plasticized Polyether(NEPE)propellant,uniaxial tensile tests were conducted using the selfmade c...In order to study the influences of confining pressure and strain rate on the mechanical properties of the Nitrate Ester Plasticized Polyether(NEPE)propellant,uniaxial tensile tests were conducted using the selfmade confining pressure system and material testing machine.The stress-strain responses of the NEPE propellant under different confining pressure conditions and strain rates were obtained and analyzed.The results show that confining pressure and strain rate have a remarkably influence on the mechanical responses of the NEPE propellant.As confining pressure increases(from 0 to 5.4 MPa),the maximum tensile stress and ultimate strain increase gradually.With the coupled effects of confining pressure and strain rate,the value of the maximum tensile stress and ultimate strain at 5.4 MPa and 0.0667 s^(-1)is 2.03 times and 2.19 times of their values under 0 MPa and 0.00333 s^(-1),respectively.Afterwards,the influence mechanism of confining pressure on the NEPE propellant was analyzed.Finally,based on the viscoelastic theory and continuous damage theory,a nonlinear constitutive model considering confining pressure and strain rate was developed.The damage was considered to be rate-dependent and pressuredependent.The constitutive model was validated by comparing experimental data with predictions of the constitutive model.The whole maximum stress errors of the model predictions are lower than 4%and the corresponding strain errors are lower than 7%.The results show that confining pressure can suppress the damage initiation and evolution of the NEPE propellant and the nonlinear constitutive model can describe the mechanical responses of the NEPE propellant under various confining pressure conditions and strain rates.This research can lay a theoretical foundation for analyzing the structural integrity of propellant grain accurately under working pressure loading.展开更多
Based on Taylor series expansion and strain components expressions of elastic mechanics, we derive formulae of strain and rotation tensor for small arrays in spherical coordinates system. By linearization process of t...Based on Taylor series expansion and strain components expressions of elastic mechanics, we derive formulae of strain and rotation tensor for small arrays in spherical coordinates system. By linearization process of the formulae, we also derive expressions of strain components and Euler vector uncertainties respectively for subnets using the law of error propagation. Taking GPS velocity field in Sichuan-Yunnan area as an example, we compute dilation rate and maximum shear strain rate field using the above procedure, and their characteristics are preliminarily car- ried on. Limits of the strain model for small array are also discussed. We make detailed explanations on small array method and the choice of small arrays. How to set weights of GPS observations are further discussed. Moreover relationship between strain and radius of GPS subnets is also analyzed.展开更多
Based on simplified axisymmetrical forming model, a elasto-plastic FEM simulation system of multi-pass conventional spinning is developed. Taking the typical draw-spinning as the study object, and establishing reasona...Based on simplified axisymmetrical forming model, a elasto-plastic FEM simulation system of multi-pass conventional spinning is developed. Taking the typical draw-spinning as the study object, and establishing reasonable mechanics model, research on the first pass of spinning process is carried out with FEM system developed. The distributions of the stress and strain are obtained by three types of roller-trace curves: straight line, involute curves and quadratic curves. The results are as follows: (1) The values of equivalent stress and strain are the lowest under involute curve compared to other two curves, and they change relatively small and decrease with the increase of radius. The values of equivalent stress and strain is the highest under quadratic curves, and increase with the increase of radius. (2) The value of radial stress is smallest under involute curve, and is the largest under straight line. Value of radial stress is often used as the criterion of cracking limit, so its distribution laws can provide references for studying the condition of cracking in multi-pass conventional spinning under different roller-trace. (3) Tangential stress is compressive stress. Absolute value of tangential stress is the smallest under involute curve, and values of tangential stress are close between other two curves. The distribution laws of tangential stress can serve as a significant guide to research the critical condition of wrinkling in multi-pass conventional spinning under different roller-trace. (4) The reduction of thickness is the smallest under involute curve. The distribution of the thickness strain is very unequal under quadratic curves. The results obtained can provide references for selecting reasonable roller-trace in multi-pass conventional spinning.展开更多
Heat strain experienced by individuals wearing chemical protective clothing(CPC)is severe and dangerous especially in hot-humid environment.The development of material science and interdisciplinary studies including e...Heat strain experienced by individuals wearing chemical protective clothing(CPC)is severe and dangerous especially in hot-humid environment.The development of material science and interdisciplinary studies including ergonomics,physiology and heat transfer is urgently required for the reduction of heat strain.The aim of this paper was to study the relationship among clothing thermal properties,physiological responses and environmental conditions.Three kinds of CPC were selected.Eight participants wore CPC and walked(4 km/h,two slopes with 5%and 10%)on a treadmill in an environment with(35±0.5)℃ and RH of(60±5)%.Core temperature,mean skin temperature,heart rate,heat storage and tolerance time were recorded and analyzed.Physiological responses were significantly affected by the clothing thermal properties and activity intensity in hot-humid environment.The obtained results can help further development of heat strain model.New materials with lower evaporative resistance and less weight are necessary to release the heat strain in hot-humid environments.展开更多
In order to reveal the changing law of the mechanical response of asphalt pavements under the action of vehicle load and provide references for the design of durable pavements,three typical asphalt pavement structures...In order to reveal the changing law of the mechanical response of asphalt pavements under the action of vehicle load and provide references for the design of durable pavements,three typical asphalt pavement structures with flexible base(S1),combined base(S2),and semi-rigid base(S3)were selected to perform field strain tests under static and dynamic load using the fiber Bragg grating optical sensing technology.The changing characteristics of the strain field along the horizontal and depth directions of pavements were analyzed.The results indicate that the most unfavorable asphalt pavement layers were the upper-middle surface layer and the lower base layer.In addition,the most unfavorable loading positions on the surface layer and the base layer were the center of wheel load and the gap center between two wheels,respectively.The most unfavorable layer of the surface layers gradually moved from the lower layer to the upper layer with the increase of base layer modulus.The power function relationships between structural layer strain and vehicle speed were revealed.The semi-rigid base asphalt pavement was the most durable pavement type,since its strain value was lower compared to those of the other structures.展开更多
Due to the current trend towards lightweight design in automotive industry,hollow stepped gear shafts for automobile and its radial forging process are widely investigated.Utilizing coupled finite element thermo-mecha...Due to the current trend towards lightweight design in automotive industry,hollow stepped gear shafts for automobile and its radial forging process are widely investigated.Utilizing coupled finite element thermo-mechanical model,radial forging process of a hollow stepped gear shaft for automobile was simulated.The optimal combination of three process parameters including initial temperature,rotation rate and radial reduction was also selected using orthogonal design method.To examine the strain inhomogeneity of the forging workpiece,the strain inhomogeneity factor was introduced.The results reveal that the maximum effective strain and the minimum effective strain appeared in the outermost and innermost zones of different cross sections for the hollow stepped gear shaft,respectively.Optimal forging parameters are determined as a combination of initial temperature of 780°C,rotation rate of 21°/stroke and radial reduction of 3 mm.展开更多
基金financial support provided by the National Natural Science Foundation of China(Grant No.12302472)the Science and Technology Support Program of Jiangsu Province(Grant No.BK20230874)+2 种基金the Aeronautical Science Fund(ASF)(Grant No.2023Z057052005)the Research Fund of State Key Laboratory of Mechanics and Control for Aerospace Structures(Nanjing University of Aeronautics and Astronautics)(Grant No.MCAS-I-0124G02)the funding received from Jiangsu Hanvo Safety Product Co.,Ltd。
文摘High-performance fiber fabrics and composites experienced transverse compression deformation at ultrahigh strain rates near the impact point when subjected to high-velocity impacts,which significantly affected their ballistic limits.In this paper,a fiber-scale experimental method for characterizing ultrahigh strain-rate transverse compression behavior was proposed.To begin with,in order to measure the extremely low stress and strain in small specimens,the conventional Hopkinson bar was reduced to the hundred-micron scale,thereby achieving wave impedance matching with single fibers.In addition,tangential and normal laser Doppler velocimetry(LDV)methods were employed to realize non-contact,high-precision,and high-speed axial velocity measurements of micron-scale incident and transmission bars,respectively.Meanwhile,a microscopic observation system was used to facilitate the installation of miniature fiber samples.The experimental setup and procedures were introduced,and the system accuracy was verified through sample-free loading tests based on one-dimensional stress wave propagation theory.Dynamic compression experiments on Graphene-UHMWPE fibers were carried out,followed by post-compression microstructural characterization via scanning electron microscopy(SEM).Results demonstrated that successful mechanical characterization was achieved at strain rates exceeding 105,an order of magnitude higher than the previously reported maximum rates.Furthermore,during the loading process,the fibers underwent uniform compression deformation while exhibiting pronounced strain-rate effects.This method offers a novel approach for dynamic mechanical characterization of microscale single fibers,enabling the development of comprehensive strain-ratedependent material models to guide the design of advanced composites and high-performance fibers.
基金the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 101034425 for the project titled A2M2TECHThe Scientific and Technological Research Council of Türkiye (TUBITAK) with grant No 120C158 for the same A2M2TECH project under the TUBITAK's 2236/B program
文摘Recent advances in additive manufacturing have enabled the construction of metallic lattice structures with tailored mechanical and functional properties.One potential application of metallic lattice struc-tures is in the impact load mitigation where an external kinetic energy is absorbed by the deformation/crushing of lattice cells.This has motivated a growing number of experimental and numerical studies,recently,on the crushing behavior of additively produced lattice structures.The present study overviews the dynamic and quasi-static crushing behavior of additively produced Ti64,316L,and AlSiMg alloy lattice structures.The first part of the study summarizes the main features of two most commonly used additive processing techniques for lattice structures,namely selective-laser-melt(SLM)and electro-beam-melt(EBM),along with a description of commonly observed process induced defects.In the second part,the deformation and strain rate sensitivities of the selected alloy lattices are outlined together with the most widely used dynamic test methods,followed by a part on the observed micro-structures of the SLM and EBM-processed Ti64,316L and AlSiMg alloys.Finally,the experimental and numerical studies on the quasi-static and dynamic compression behavior of the additively processed Ti64,316L,and AlSiMg alloy lattices are reviewed.The results of the experimental and numerical studies of the dynamic properties of various types of lattices,including graded,non-uniform strut size,hollow,non-uniform cell size,and bio-inspired,were tabulated together with the used dynamic testing methods.The dynamic tests have been noted to be mostly conducted in compression Split Hopkinson Pressure Bar(SHPB)or Taylor-and direct-impact tests using the SHPB set-up,in all of which relatively small-size test specimens were tested.The test specimen size effect on the compression behavior of the lattices was further emphasized.It has also been shown that the lattices of Ti64 and AlSiMg alloys are relatively brittle as compared with the lattices of 316L alloy.Finally,the challenges associated with modelling lattice structures were explained and the micro tension tests and multi-scale modeling techniques combining microstructural characteristics with macroscopic lattice dynamics were recommended to improve the accuracy of the numerical simulations of the dynamic compression deformations of metallic lattice structures.
基金supported by the National Natural Science Foundation of China(52002366,22075263,22571288)the Fundamental Research Funds for the Central Universities(WK2060000091,WK2060250115,WK2060000039)the Students’Innovation and Entrepreneurship Foundation of USTC(CY2023C021).
文摘The slow kinetics of the cathode CO_(2) reduction reaction and the decomposition reaction of Li2CO3,a widebandwidth insulating product,lead to difficult CO_(2) capture and high charging potential in Li-CO_(2) batteries.To improve the reaction kinetics and decrease the reaction overpotential,we synthesized mesoporous Pt nanosheets with high tensile strain.The presence of many unsaturated coordinated Pt atoms around the pores gives rise to tensile strain in the mesoporous Pt nanosheets.This tensile strain plays a key role in regulating the interactions between the catalytic surface of Pt and the adsorbed intermediates.The two-dimensional structure provides more active sites on the surface for the catalytic reactions.These superiorities enable a low overpotential of 0.36 V at a cutoff capacity of 100μAh·cm^(−2) at a current density of 10μA·cm^(−2) over more than 2000 h.This study opens new possibilities for the rational design of metal-based materials with strain engineering for electrochemical energy storage.
文摘Quasi-static and high strain rate compressive experiments on vinyl ester casting were carried out by means of MTS (Material Test System) and Hopkinson bar. The behaviors of the compressed unstable and fracture of the resin casting at different strain rates were investigated.The results indicate that the response behavior of the resin casting is controlled by different mechanisms at different strain rate, and some mechanical properties of vinyl ester casting are rate-dependent: the casting are destroyed in toughness model under strain rate 3.3×10 -4～6.6×10 -3/s, while the casting are destroyed in brittleness model under strain rate 950～5800/s. The yield stress, yield strain energy density are all increased with the increasing strain rates at quasi-static as well as at high strain rates. What is interesting is that the yield strain decreased with the strain rates increasing at quasi-static while increased at high strain rates. It is considered that the casting occurred forcing high elastic deformation at high strain rates. The damage of the specimens is mainly controlled by axial stress before unstable deformation, while mainly controlled by shear stress after unstable deformation, and then developed to fracture finally. This progress is rate-dependent: the development of the cracks inside the castings increased with the strain rate increasing.
基金Supported by the National Natural Science Foundation of China (31101417 31101415)+1 种基金Zhejiang Provincial Natural Science Foundation of China (Y3110175 Y3110277)
文摘Citrus tristeza virus （CTV）, the most devastating viral pathogen in citrus, causes tremendous economic losses to citrus industry worldwide. The CTV isolates exhibit variable pathogenicities on their hosts indicating a mixed population of the CTV in nature. Several fragments within the CTV genome have been used for studying the genetic diversity of the CTV, however, the best region for rapid the CTV strain differentiation is still absent at present. In present study, a systemic analysis was carried out to evaluate the best region within the CTV genome for rapid CTV strain differentiation. Results of our study showed that the major coat protein （CP） coding region was the best region for this purpose. Using pair-wise distance frequency distribution plot, a reasonable genetic distance cut-off value was set for the CTV CP gene for the CTV strain differentiation. Using this criterion, eight CTV strains, including seven well characterized and a new strain, were successfully differentiated using 537 CTV isolates reported from 38 countries. The global strain distribution pattern was then determined and discussed. Our results also provided a new insight into the evolution and spreading of the virus, as well as the information for developing proper disease management strategy.
基金Project of State Science and Technology in the Eleventh "Five-year Plan" (2006BAC01B02-02-03).
文摘On the basis of the GPS data obtained from repeated measurements carried out in 2004 and 2007,the horizontal principal strain of the Chinese mainland is calculated,which shows that the direction of principal compressive strain axis of each subplate is basically consistent with the P-axis of focal mechanism solution and the principal compressive stress axis acquired by geological method.It indicates that the crustal tectonic stress field is relatively stable in regions in a long time.The principal compressive stress axes of Qinghai-Tibet and Xinjiang subplates in the western part of Chinese mainland direct to NS and NNE-SSW,which are controlled by the force from the col-lision of the Eurasia Plate and India Plate.The principal compressive strain axes of Heilongjiang and North China subplates in the eastern part direct to ENE-WSW,which shows that they are subject to the force from the collision and underthrust of the Eurasia Plate to the North America and Pacific plates.At the same time,they are also af-fected by the lateral force from Qinghai-Tibet and Xinjiang subplates.The principal compressive strain axis of South China plate is WNW-ESE,which reflects that it is affected by the force from the collision of Philippine Sea Plate and Eurasia Plate and it is also subject to the lateral force from Qinghai-Tibet subplate.It is apparent from the comparison between the principal compressive strain axes in the periods of 2004～2007 and 2001～2004 that the acting directions of principal compressive stress of subplates in both periods are basically consistent.However,there is certain difference between their directional concentrations of principal compressive stress axes.The sur-face strain rates of different tectonic units in both periods indicate that the events predominating by compressive variation decrease,while the events predominating by tensile change increase.
基金the National Natural Science Foundation of China(Grant No.51606098)Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX20_0303).
文摘In order to study the influences of confining pressure and strain rate on the mechanical properties of the Nitrate Ester Plasticized Polyether(NEPE)propellant,uniaxial tensile tests were conducted using the selfmade confining pressure system and material testing machine.The stress-strain responses of the NEPE propellant under different confining pressure conditions and strain rates were obtained and analyzed.The results show that confining pressure and strain rate have a remarkably influence on the mechanical responses of the NEPE propellant.As confining pressure increases(from 0 to 5.4 MPa),the maximum tensile stress and ultimate strain increase gradually.With the coupled effects of confining pressure and strain rate,the value of the maximum tensile stress and ultimate strain at 5.4 MPa and 0.0667 s^(-1)is 2.03 times and 2.19 times of their values under 0 MPa and 0.00333 s^(-1),respectively.Afterwards,the influence mechanism of confining pressure on the NEPE propellant was analyzed.Finally,based on the viscoelastic theory and continuous damage theory,a nonlinear constitutive model considering confining pressure and strain rate was developed.The damage was considered to be rate-dependent and pressuredependent.The constitutive model was validated by comparing experimental data with predictions of the constitutive model.The whole maximum stress errors of the model predictions are lower than 4%and the corresponding strain errors are lower than 7%.The results show that confining pressure can suppress the damage initiation and evolution of the NEPE propellant and the nonlinear constitutive model can describe the mechanical responses of the NEPE propellant under various confining pressure conditions and strain rates.This research can lay a theoretical foundation for analyzing the structural integrity of propellant grain accurately under working pressure loading.
基金State Key Basic Research Development and Programming Project of China (2004CB418403)Special Foundation of Seismological Science (200708030)Basic Scientific Research Program of Institute of Earthquake Science (2007-22)
文摘Based on Taylor series expansion and strain components expressions of elastic mechanics, we derive formulae of strain and rotation tensor for small arrays in spherical coordinates system. By linearization process of the formulae, we also derive expressions of strain components and Euler vector uncertainties respectively for subnets using the law of error propagation. Taking GPS velocity field in Sichuan-Yunnan area as an example, we compute dilation rate and maximum shear strain rate field using the above procedure, and their characteristics are preliminarily car- ried on. Limits of the strain model for small array are also discussed. We make detailed explanations on small array method and the choice of small arrays. How to set weights of GPS observations are further discussed. Moreover relationship between strain and radius of GPS subnets is also analyzed.
文摘Based on simplified axisymmetrical forming model, a elasto-plastic FEM simulation system of multi-pass conventional spinning is developed. Taking the typical draw-spinning as the study object, and establishing reasonable mechanics model, research on the first pass of spinning process is carried out with FEM system developed. The distributions of the stress and strain are obtained by three types of roller-trace curves: straight line, involute curves and quadratic curves. The results are as follows: (1) The values of equivalent stress and strain are the lowest under involute curve compared to other two curves, and they change relatively small and decrease with the increase of radius. The values of equivalent stress and strain is the highest under quadratic curves, and increase with the increase of radius. (2) The value of radial stress is smallest under involute curve, and is the largest under straight line. Value of radial stress is often used as the criterion of cracking limit, so its distribution laws can provide references for studying the condition of cracking in multi-pass conventional spinning under different roller-trace. (3) Tangential stress is compressive stress. Absolute value of tangential stress is the smallest under involute curve, and values of tangential stress are close between other two curves. The distribution laws of tangential stress can serve as a significant guide to research the critical condition of wrinkling in multi-pass conventional spinning under different roller-trace. (4) The reduction of thickness is the smallest under involute curve. The distribution of the thickness strain is very unequal under quadratic curves. The results obtained can provide references for selecting reasonable roller-trace in multi-pass conventional spinning.
文摘Heat strain experienced by individuals wearing chemical protective clothing(CPC)is severe and dangerous especially in hot-humid environment.The development of material science and interdisciplinary studies including ergonomics,physiology and heat transfer is urgently required for the reduction of heat strain.The aim of this paper was to study the relationship among clothing thermal properties,physiological responses and environmental conditions.Three kinds of CPC were selected.Eight participants wore CPC and walked(4 km/h,two slopes with 5%and 10%)on a treadmill in an environment with(35±0.5)℃ and RH of(60±5)%.Core temperature,mean skin temperature,heart rate,heat storage and tolerance time were recorded and analyzed.Physiological responses were significantly affected by the clothing thermal properties and activity intensity in hot-humid environment.The obtained results can help further development of heat strain model.New materials with lower evaporative resistance and less weight are necessary to release the heat strain in hot-humid environments.
基金Projects(51908071,51708071)supported by National Natural Science Foundation of ChinaProject(2020JJ5975)supported by the Natural Science Foundation of Hunan Province,China+1 种基金Project(18C0194)supported by the Scientific Research Project of Education Department of Hunan Province,ChinaProject(kfj190301)supported by Open Fund of Key Laboratory of Road Structure and Material of Ministry of Transport(Changsha University of Science&Technology),China。
文摘In order to reveal the changing law of the mechanical response of asphalt pavements under the action of vehicle load and provide references for the design of durable pavements,three typical asphalt pavement structures with flexible base(S1),combined base(S2),and semi-rigid base(S3)were selected to perform field strain tests under static and dynamic load using the fiber Bragg grating optical sensing technology.The changing characteristics of the strain field along the horizontal and depth directions of pavements were analyzed.The results indicate that the most unfavorable asphalt pavement layers were the upper-middle surface layer and the lower base layer.In addition,the most unfavorable loading positions on the surface layer and the base layer were the center of wheel load and the gap center between two wheels,respectively.The most unfavorable layer of the surface layers gradually moved from the lower layer to the upper layer with the increase of base layer modulus.The power function relationships between structural layer strain and vehicle speed were revealed.The semi-rigid base asphalt pavement was the most durable pavement type,since its strain value was lower compared to those of the other structures.
基金Projects(51774054,51974050)supported by the National Natural Science Foundation of China。
文摘Due to the current trend towards lightweight design in automotive industry,hollow stepped gear shafts for automobile and its radial forging process are widely investigated.Utilizing coupled finite element thermo-mechanical model,radial forging process of a hollow stepped gear shaft for automobile was simulated.The optimal combination of three process parameters including initial temperature,rotation rate and radial reduction was also selected using orthogonal design method.To examine the strain inhomogeneity of the forging workpiece,the strain inhomogeneity factor was introduced.The results reveal that the maximum effective strain and the minimum effective strain appeared in the outermost and innermost zones of different cross sections for the hollow stepped gear shaft,respectively.Optimal forging parameters are determined as a combination of initial temperature of 780°C,rotation rate of 21°/stroke and radial reduction of 3 mm.
