The warm and ice-rich frozen soil is characterized by high unfrozen water content, low shear strength and large compressibility, which is unreliable to meet the stability requirements of engineering infrastructures an...The warm and ice-rich frozen soil is characterized by high unfrozen water content, low shear strength and large compressibility, which is unreliable to meet the stability requirements of engineering infrastructures and foundations in permafrost regions. In this study, a novel approach for stabilizing the warm and ice-rich frozen soil with sulphoaluminate cement was proposed based on chemical stabilization. The mechanical behaviors of the stabilized soil, such as strength and stress-strain relationship, were investigated through a series of triaxial compression tests conducted at -1.0℃, and the mechanism of strength variations of the stabilized soil was also explained based on scanning electron microscope test. The investigations indicated that the strength of stabilized soil to resist failure has been improved, and the linear Mohr-Coulomb criteria can accurately reflect the shear strength of stabilized soil under various applied confining pressure. The increase in both curing age and cement mixing ratio were favorable to the growth of cohesion and internal friction angle. More importantly, the strength improvement mechanism of the stabilized soil is attributed to the formation of structural skeleton and the generation of cementitious hydration products within itself. Therefore, the investigations conducted in this study provide valuable references for chemical stabilization of warm and ice-rich frozen ground, thereby providing a basis for in-situ ground improvement for reinforcing warm and ice-rich permafrost foundations by soil-cement column installation.展开更多
This paper reviews the major achievements in terms of mechanical behaviors of coal measures,mining stress distribution characteristics and ground control in China’s deep underground coal mining.The three main aspects...This paper reviews the major achievements in terms of mechanical behaviors of coal measures,mining stress distribution characteristics and ground control in China’s deep underground coal mining.The three main aspects of this review are coal measure mechanics,mining disturbance mechanics,and rock support mechanics.Previous studies related to these three topics are reviewed,including the geo-mechanical properties of coal measures,distribution and evolution characteristics of mining-induced stresses,evolution characteristics of mining-induced structures,and principles and technologies of ground control in both deep roadways and longwall faces.A discussion is made to explain the structural and mechanical properties of coal measures in China’s deep coal mining practices,the types and dis-tribution characteristics of in situ stresses in underground coal mines,and the distribution of mining-induced stress that forms under different geological and engineering conditions.The theory of pre-tensioned rock bolting has been proved to be suitable for ground control of deep underground coal roadways.The use of combined ground control technology(e.g.ground support,rock mass modification,and destressing)has been demonstrated to be an effective measure for rock control of deep roadways.The developed hydraulic shields for 1000 m deep ultra-long working face can effectively improve the stability of surrounding rocks and mining efficiency in the longwall face.The ground control challenges in deep underground coal mines in China are discussed,and further research is recommended in terms of theory and technology for ground control in deep roadways and longwall faces.展开更多
To improve the defense capability of military equipment under extreme conditions,impact-resistant and high-energy-consuming materials have to be developed.The damping characteristic of entangled porous metallic wire m...To improve the defense capability of military equipment under extreme conditions,impact-resistant and high-energy-consuming materials have to be developed.The damping characteristic of entangled porous metallic wire materials(EPMWM)for vibration isolation was previously investigated.In this paper,a study focusing on the impact-resistance of EPMWM with the consideration of ambient temperature is presented.The quasi-static and low-velocity impact mechanical behavior of EPMWM under different temperatures(25℃-300℃)are systematically studied.The results of the static compression test show that the damping energy dissipation of EPMWM increases with temperature while the nonlinear damping characteristics are gradually enhanced.During the impact experiments,the impact energy loss rate of EPMWM was between 65%and 85%,while the temperatures increased from 25℃to 300℃.Moreover,under the same drop impact conditions,the overall deformation of EPMWM decreases in the temperature range of 100℃-200℃.On the other hand,the impact stiffness,energy dissipation,and impact loss factor of EPMWM significantly increase with temperature.This can be attributed to an increase in temperature,which changes the thermal expansion coefficient and contact state of the internal wire helixes.Consequently,the energy dissipation mode(dry friction,air damping,and plastic deformation)of EPMWM is also altered.Therefore,the EPMWM may act as a potential candidate material for superior energy absorption applications.展开更多
One-stage light gas gun was utilized to study the dynamic mechanical properties of AD90 alumina subjected to the shock loading. Manganin gauges were adopted to obtain the stress-time histories. The velocity interferom...One-stage light gas gun was utilized to study the dynamic mechanical properties of AD90 alumina subjected to the shock loading. Manganin gauges were adopted to obtain the stress-time histories. The velocity interferometer system for any reflector (VISAR) was used to obtain the free surface velocity profile and determine the Hugoniot elastic limit. The Hugoniot curves were fitted with the experimental data. From Hugoniot curves the compressive behaviors of AD90 alumina were found to change typically from elastic to "plastic". The dynamic mechanical behaviors for alumina under impact loadings were analyzed by using the path line principle of Lagrange analysis, including the nonlinear characteristics, the strain rate dependence, the dispersion and declination of shock wave in the material. A damage model applicable to ceramics subjected to dynamic compressive loading has been developed. The model was based on the damage micromechanics and wing crack nucleation and growth. The effects of parameters of both the micro-cracks nucleation and the initial crack size on the dynamic fracture strength were discussed. The results of the dynamic damage evolution model were compared with the experimental results and a good agreement was found.展开更多
The mechanical behaviors and the microstructural characteristics of TC11 alloy with quenched martensite microstructure during hot compressive deformation were investigated. It shows that at various temperatures and st...The mechanical behaviors and the microstructural characteristics of TC11 alloy with quenched martensite microstructure during hot compressive deformation were investigated. It shows that at various temperatures and strain rates, the stress strain curves firstly exhibit strain hardening, then strain softening and finally reach the steady deformation state; in the meanwhile, the initial lamellar microstructure is transformed into the equiaxed and uniform one through dynamic recrystallization. It shows that the present TC11 alloy has different Z D relationships in relatively lower temperature (RLT) range and relatively higher temperature (RHT) range, which is believed to be due to different deformation activation energies. During RHT deformation, dynamic recrystallization occurs in both α phases and β phases, but during RLT deformation, dynamic recrystallization only occurs in α phases and in the meanwhile β phases undergo a process of precipitation and growth.展开更多
The ZrO2-Al2O3 ceramic composites were prepared by appropriate techniques with commercial ZrO2 and Al2O3 powders as raw materials and Y2O3 as stabilizer. The results indicate that with the introduction of Al2O3 into t...The ZrO2-Al2O3 ceramic composites were prepared by appropriate techniques with commercial ZrO2 and Al2O3 powders as raw materials and Y2O3 as stabilizer. The results indicate that with the introduction of Al2O3 into the ZrO2 matrix where the quantity of additive Y2O3 is 3.5% (mole fraction), the growth of ZrO2 grains is efficiently inhibited, which helps the ZrO2 grains exist in a metastable tetragonal manner; thus higher strength and toughness are acquired. When the content of alumina is 20% (mass fraction), the bending strength and fracture toughness of the composites are 676.7 MPa and 10 MPa·m1/2 respectively, the mechanical behaviors are close to those prepared with ZrO2 and Al2O3 powders synthesized through wet chemical approach. The mechanical behaviors of the composites are well improved owing to the dispersion toughening of alumina grains and phase transformation toughening of zirconia grains.展开更多
The basic mechanical behaviors of high density polyethylene electrofusion welded joint at different temperatures were studied by using differently designed specimens in this paper. The results show that the strength o...The basic mechanical behaviors of high density polyethylene electrofusion welded joint at different temperatures were studied by using differently designed specimens in this paper. The results show that the strength of weld bonding plane is higher than that of the pipe and socket materials at room temperature. In order to get the shear strength of electrofusion welded joint, the effective bond lengths were reduced by cutting artificial groove through the socket. The effective bonding length of welded joint to get the shear strength is decreased with decreasing testing temperature. The shear strength and the sensibility to sharp notch of HDPE material increased with decreasing temperature.展开更多
The simplified mechanical model and finite element model are established on the basis of the measured results and analysis of the grouting pile deformation monitoring,surface horizontal displacement and vertical displ...The simplified mechanical model and finite element model are established on the basis of the measured results and analysis of the grouting pile deformation monitoring,surface horizontal displacement and vertical displacement monitoring,deep horizontal displacement(inclinometer)monitoring,soil pressure monitoring and seepage pressure monitoring in the lower reaches of Wuan River regulation project in Shishi,Fujian Province.The mechanical behavior and deformation performance of mould-bag pile retaining wall formed after controlled cement grouting in the silty stratum of the test section are analyzed and compared.The results show that the use of controlled cement grouting mould-bag pile technology is to strengthen the soft stratum for sealing water and reinforcement,so that it can rock into a retaining wall,which can both retain soil and seal water with excellent effect.The control of cement grouting technology not only makes the soft soil rock in the range of retaining wall of mould-bag pile,but also makes a wide range of soil around the mould-bag pile squeeze and embed to compaction;and its cohesion and internal friction angle increased,so as to achieve the purpose of reducing soil pressure and improving mechanical and deformation properties of retaining wall.展开更多
In order to characterize the mechanical behaviors of the Velcro~? and Dual-lock fasteners, a series of tests including the butt-joint(BJ) monotonic tensile and shear, mixed tensile-shear with various loading angles, t...In order to characterize the mechanical behaviors of the Velcro~? and Dual-lock fasteners, a series of tests including the butt-joint(BJ) monotonic tensile and shear, mixed tensile-shear with various loading angles, the loading rates effects, the double cantilever beam(DCB) fracture and 180° peel experiments were performed. The tensile and shear tests results showed that the mechanical behaviors of Velcro~? fastener separation are analogous to ductile materials, and those of Dual-lock fasteners are more like brittle ones. The mixed tensile-shear with various loading angles tests results demonstrated that magnitudes of the peak stresses in 30°, 45°, and 60° have no significant differences, which are lower than those in the monotonic tensile or shear tests for the two fasteners. The effects of the loading rate tests show that the peak stresses of the Velcro~? fastener manifested good performance at the loading rate of 10 to 20 mm/min in the tensile and shear conditions, and the Dual-lock did it well around the loading rates of 10 to 20 mm/min in the tensile condition. The cohesive zone model(CZM) is employed to numerical predict the DCB fracture and the 180° peel tests. The CZM predictions results are proven to commendably capture the two tests separation processes, of the tow fasteners, and the numerical results agreed well with the peeling tests data of the Dual lock fasteners. The results and discussions in this study are expected to bring more understanding to engineers and designers about the performance of Velcro~? and Dual lock fasteners.展开更多
This Special Issue of the Journal of Rock Mechanics and GeotechnicalEngineering (JRMGE) contains 13 papers prepared by internationalexperts on various general topics in geomechanics, rockmechanics and geotechnical e...This Special Issue of the Journal of Rock Mechanics and GeotechnicalEngineering (JRMGE) contains 13 papers prepared by internationalexperts on various general topics in geomechanics, rockmechanics and geotechnical engineering. It represents a usefulmix of theoretical developments, testing and practical applications.We present in the following brief details in the papers, alphabeticallyin accordance with the last name of the first author.Barla presents a review of tunneling techniques with emphasison the full-face method combining full-face excavation and facereinforcement by means of fiber-glass elements with a yieldcontrolsupport. This method has been used successfully in difficultgeologic conditions, and for a wide spectrum of ground situations.The validation of the method with respect to the Saint Martin LaPorte access adit along the LyoneTurin Base tunnel experiencingseverely squeezing conditions during excavation is also includedin the paper. The numerical modeling with consideration of therock mass time-dependent behavior showed a satisfactory agreementwith monitoring results.展开更多
The hysteresis unit system was introduced to mechanical structure behavior of the TiNi SMA joint based on the structure characteristics of the martensite variants in the joints, and some functions reflecting its inner...The hysteresis unit system was introduced to mechanical structure behavior of the TiNi SMA joint based on the structure characteristics of the martensite variants in the joints, and some functions reflecting its inner structure characteristics and micro-behavior such as density function, phase transformation function were set up from micro-points. Finally, the structure behavior relationship and corresponding mathematic model reflecting the relationship among hysteresis strain, stress and phase transformation strain were provided, which could predict the stress-strain behavior of the TiNi SMA joint to large extent.展开更多
The effects of two types of additives, Y2O3 and Dy2O3, on the sintering and mechanical behaviors of AlN ceramics were investigated. The experimental results show that the sintering temperature can be decreased and the...The effects of two types of additives, Y2O3 and Dy2O3, on the sintering and mechanical behaviors of AlN ceramics were investigated. The experimental results show that the sintering temperature can be decreased and the mechanical behavior can be improved by adding rare earth in AlN ceramics. The strength of AlN ceramics with Y2O3 and Dy2O3 are 326 and 320 MPa, respectively, which are 97.6% and 93.9% higher than the un-doped AlN ceramics. The fracture behavior on the fracture surfaces of rare earth oxide AlN ceramics was found to be a mixed mode of transgranular fracture and intergranular fracture. As a result, it is concluded that the improvement of bending strength of AlN ceramics with Y2O3 and Dy2O3 addition are mainly achieved by strengthening the grain boundary.展开更多
The phase equilibrium and mechanical behaviors of natural gas hydrate-bearing sediment are essential for gas recovery from hydrate reservoirs.In heating closed systems,the temperature-pressure path of hydrate-bearing ...The phase equilibrium and mechanical behaviors of natural gas hydrate-bearing sediment are essential for gas recovery from hydrate reservoirs.In heating closed systems,the temperature-pressure path of hydrate-bearing sediment deviates from that of pure bulk hydrate,reflecting the porous media effect in phase equilibrium.A generalized phase equilibrium equation was established for hydrate-bearing sediments,which indicates that both capillary and osmotic pressures cause the phase equilibrium curve to shift leftward on the temperature-pressure plane.In contrast to bulk hydrate,hydrate-bearing sediment always contains a certain amount of unhydrated water,which keeps phase equilibrium with the hydrate within the hydrate stability field.With changes in temperature and pressure,a portion of pore hydrate and unhydrated water may transform into each other,affecting the shear strength of hydrate-bearing sediment.A shear strength model is proposed to consider not only hydrate saturation but also the change in temperature and pressure of hydrate-bearing sediment.The model is validated by experimental data with various hydrate saturation,temperature and pressure conditions.The deformation induced by partial dissociation was studied through depressurization tests under constant effective stress.The reduction in gas pressure within the hydrate stability field indeed caused sediment deformation.The dissociation-induced deformation can be reasonably estimated as the difference in volume between hydrate-bearing and hydrate-free sediments from the compression curves.展开更多
Precursor-derived ceramic SiOC(PDC-SiOC)microlattices exhibit excellent oxidation resistance,high-temperature stability,and superior mechanical properties.However,the printing accuracy of the PDC-SiOC microlattices by...Precursor-derived ceramic SiOC(PDC-SiOC)microlattices exhibit excellent oxidation resistance,high-temperature stability,and superior mechanical properties.However,the printing accuracy of the PDC-SiOC microlattices by 3D printing is still limited,and mechanical properties of the PDC-SiOC microlattices have not been studied systematically.Here,PDC-SiOC octet microlattices were fabricated by projection micro stereolithography(PμSL)3D printing,and photoabsorber(Sudan III)’s effect on the accuracy was systematically analyzed.The results showed that the addition of Sudan III improved the printing accuracy significantly.Then,the ceramization process of the green body was analyzed in detail.The order of the green body decreased,and most of their chemical bonds were broken during pyrolysis.After that,the PDC-SiOC microlattices with different truss diameters in the range of 52–220μm were fabricated,and their mechanical properties were investigated.The PDC-SiOC microlattices with a truss diameter of 52μm exhibited higher compression strength(31 MPa)than those with bigger truss diameters.The size effect among the PDC-SiOC microlattices was analyzed.Our work provides a deeper insight into the manufacturing of PDC-SiOC micro-scaled architectures by 3D printing and paves a path to the research of the size effect in ceramic structures.展开更多
Rock bolts are widely employed as an effective and efficient reinforcement method in geotechnical engineering.Sandwich composite structures formed by hard rock and weak rock are often encountered in practical projects...Rock bolts are widely employed as an effective and efficient reinforcement method in geotechnical engineering.Sandwich composite structures formed by hard rock and weak rock are often encountered in practical projects.Furthermore,the spatial structure of the rock mass has a direct influence on the effect of the anchorage support.To investigate the impact of rock mass structure on the mechanical characteristics of anchorage interfaces,pull-out tests on reinforced specimens with different mudstone thicknesses and fracture dip angles are conducted.The experimental results indicate that the percentage of mudstone content and fracture dip angle have a significant influence on the pullout load of the samples.A weaker surrounding rock results in a lower peak load and a longer critical anchorage length,and vice versa.The results also show that 70%mudstone content can be considered a critical condition for impacting the peak load.Specifically,the percentage of mudstone content has a limited influence on the variation in the peak load when it exceeds 70%.Optical fiber deformation results show that compared to the rock mass with fracture dip angles of 0°and 60°,the rock mass with a fracture dip angle of 30°has a more uniformly distributed force at the anchorage interface.When the fracture dip angle exceeds 60°,the dip angle is no longer a key indicator of peak load.The accuracy of the experimentally obtained load-displacement curves is further verified although numerical simulation using the discrete element method.展开更多
Al Si10Mg porous protective structure often produces different damage forms under compressive loading,and these damage modes affect its protective function.In order to well meet the service requirements,there is an ur...Al Si10Mg porous protective structure often produces different damage forms under compressive loading,and these damage modes affect its protective function.In order to well meet the service requirements,there is an urgent need to comprehensively understand the mechanical behavior and response mechanism of AlSi10Mg porous structures under compressive loading.In this paper,Al Si10Mg porous structures with three kinds of volume fractions are designed and optimized to meet the requirements of high-impact,strong-energy absorption,and lightweight characteristics.The mechanical behaviors of AlSi10Mg porous structures,including the stress-strain relationship,structural bearing state,deformation and damage modes,and energy absorption characteristics,were obtained through experimental studies at different loading rates.The damage pattern of the damage section indicates that AlSi10Mg porous structures have both ductile and brittle mechanical properties.Numerical simulation studies show that the AlSi10Mg porous structure undergoes shear damage due to relative misalignment along the diagonal cross-section,and the damage location is almost at 45°to the load direction,which is the most direct cause of its structural damage,revealing the damage mechanism of AlSi10Mg porous structures under the compressive load.The normalized energy absorption model constructed in the paper well interprets the energy absorption state of Al Si10Mg porous structures and gives the sensitive location of the structures,and the results of this paper provide important references for peers in structural design and optimization.展开更多
Full understanding of the thermomechanical behaviors of materials at high strain rates and high temperatures are of great importance from not only scientific meaning but also practical value in engineering structure d...Full understanding of the thermomechanical behaviors of materials at high strain rates and high temperatures are of great importance from not only scientific meaning but also practical value in engineering structure design and safety assessment.Great efforts have been made for abilities of operation the split Hopkinson bars,the most popular technique for experimental determination of mechanical behaviors of materials over the strain rates from 10^2 to 10^4 s^−1 over the past 70 years,at high temperatures since 1960s.A review of experiment work is presented in this paper to give an overview of the development of experimental techniques at high temperatures based on Hopkinson bar systems.The principles of the split Hopkinson bar requires the loading bars avoiding temperature gradient or keeping relatively low temperature when performing high temperature testing.Techniques such as performing temperature gradient corrections,rapid heating or using special designed automatically assembled systems were proposed by researchers to enable the operation of the split Hopkinson bars at temperature as high as possible.Moreover,to the application of high speed photographic technique for capturing the dynamic deformation process of the specimen in high temperature Hopkinson bar testing,some key issues of eliminating the strong thermal radiation induced lights oversaturation and de-blurring of images due to insufficient exposure at high temperature and high strain rate condition,as well as fabrication of high contrast speckle pattern for high temperature digital image correlation measurement were also proposed.The technique can now enable the split Hopkinson bar testing to be performed at high temperature up to 1873 K under the loading conditions of compression or tension with the in situ observation and full field measurement of deformation as well.The paper concludes with summaries of the most important achievements and highlighting of the prospects,trends and remaining challenges for future research.展开更多
In this work,we present a new piezoelectric solid solution consisting of two typical alkali niobate-based materials,K_(0.5)Na_(0.5)NbO_(3)(KNN)and Li_(0.15)Na_(0.85)NbO_(3)(LNN).Although KNN and LNN have the same pero...In this work,we present a new piezoelectric solid solution consisting of two typical alkali niobate-based materials,K_(0.5)Na_(0.5)NbO_(3)(KNN)and Li_(0.15)Na_(0.85)NbO_(3)(LNN).Although KNN and LNN have the same perovskite structure,they exhibit extremely different electrical properties and mechanical behaviors.The phase structures,electrical and mechanical evolutions of the new lead-free piezoelectric materials with different ratios of KNN and LNN are comprehensively and theoretically investigated.According to the Xray diffraction patterns and curves of permittivity versus temperature,a series of complicated phase transitions can be found with varied LNN content.Rietveld refinement results based on XRD patterns reveal an oxygen octahedron tilting in the LNN-rich crystal structure,and simultaneously the reasons for octahedron tilting are discussed.The distorted crystal structure is accompanied by extremely decreased electric properties but increased mechanical properties,which reveals electrical and mechanical properties of alkali niobate-based piezoelectric ceramics strongly depend on their inner structures,and the enhancement of intrinsic hardness results in the deterioration of piezoelectric properties.Our work exhibits the detailed evolutions of structure,electrical and mechanical properties from KNN to LNN,which provides experimental and theoretical basis for development of new alkali niobate-based piezoelectric materials.展开更多
Current constitutive theories face challenges when predicting the extremely large deformation and fracture of hydrogels,which calls for the demands to reveal the fundamental mechanism of the various mechanical behavio...Current constitutive theories face challenges when predicting the extremely large deformation and fracture of hydrogels,which calls for the demands to reveal the fundamental mechanism of the various mechanical behaviors of hydrogels from bottom up.Proper hydrogel network model provides a better approach to bridge the gap between the micro-structure and the macroscopic mechanical responses.This work summarizes the theoretical and numerical researches on the hydrogel network models,aiming to provide new insights into the effect of microstructure on the swelling-deswelling process,hyperelasticity,viscoelasticity and fracture of hydrogels.Hydrogel network models are divided into full-atom network models,realistic network models and abstract network models.Full-atom network models have detailed atomic structure but small size.Realistic network models with different coarse-graining degree have large model size to explain the swelling-deswelling process,hyperelasticity and viscoelasticity.Abstract network models abstract polymer chains into analytical interactions,leading to the great leap of model size.It shows advantages to reproduce the crack initiation and propagation in hydrogels by simulating chain scission.Further research directions on the network modeling are suggested.We hope this work can help integrate the merits of network modeling methods and continuum mechanics to capture the various mechanical behaviors of hydrogels.展开更多
Double shoulder drill pipe joint(DSJ)is a novel thread structure which appears in recent years.Its strength reduced efficiently while the structure design is not appropriately,for the DSJ’s mechanical behaviors weren...Double shoulder drill pipe joint(DSJ)is a novel thread structure which appears in recent years.Its strength reduced efficiently while the structure design is not appropriately,for the DSJ’s mechanical behaviors weren’t well studied.In this paper a 3D whole structure finite element model of DSJ was established based on the Principle of Virtual Work,and validated the model’s computing results by experimental results.The authors analyzed the stress and strain distribution with the 3D whole structure finite element model’s computing results under torque moment,compression force,tension load,and bend moment.And then acquired the DSJ’s mechanical behaviors under each load.The research works of this paper refer accordance to recognize and design the DSJ.展开更多
基金supported by the National Natural Science Foundation of China (No. 41471062, No. 41971085, No. 41971086)。
文摘The warm and ice-rich frozen soil is characterized by high unfrozen water content, low shear strength and large compressibility, which is unreliable to meet the stability requirements of engineering infrastructures and foundations in permafrost regions. In this study, a novel approach for stabilizing the warm and ice-rich frozen soil with sulphoaluminate cement was proposed based on chemical stabilization. The mechanical behaviors of the stabilized soil, such as strength and stress-strain relationship, were investigated through a series of triaxial compression tests conducted at -1.0℃, and the mechanism of strength variations of the stabilized soil was also explained based on scanning electron microscope test. The investigations indicated that the strength of stabilized soil to resist failure has been improved, and the linear Mohr-Coulomb criteria can accurately reflect the shear strength of stabilized soil under various applied confining pressure. The increase in both curing age and cement mixing ratio were favorable to the growth of cohesion and internal friction angle. More importantly, the strength improvement mechanism of the stabilized soil is attributed to the formation of structural skeleton and the generation of cementitious hydration products within itself. Therefore, the investigations conducted in this study provide valuable references for chemical stabilization of warm and ice-rich frozen ground, thereby providing a basis for in-situ ground improvement for reinforcing warm and ice-rich permafrost foundations by soil-cement column installation.
基金This work has been supported by the National Key Research and Development Program(Grant No.2017YFC0603000)which was jointly completed by the Coal Mining Research Branch of CCRI,China University of Mining and Technology(Xuzhou and Beijing),Henan Polytechnic UniversityXinji Energy Company Limited of China Coal Energy Group.This work was also supported by the National Natural Science Foundation of China(Grant No.51927807)。
文摘This paper reviews the major achievements in terms of mechanical behaviors of coal measures,mining stress distribution characteristics and ground control in China’s deep underground coal mining.The three main aspects of this review are coal measure mechanics,mining disturbance mechanics,and rock support mechanics.Previous studies related to these three topics are reviewed,including the geo-mechanical properties of coal measures,distribution and evolution characteristics of mining-induced stresses,evolution characteristics of mining-induced structures,and principles and technologies of ground control in both deep roadways and longwall faces.A discussion is made to explain the structural and mechanical properties of coal measures in China’s deep coal mining practices,the types and dis-tribution characteristics of in situ stresses in underground coal mines,and the distribution of mining-induced stress that forms under different geological and engineering conditions.The theory of pre-tensioned rock bolting has been proved to be suitable for ground control of deep underground coal roadways.The use of combined ground control technology(e.g.ground support,rock mass modification,and destressing)has been demonstrated to be an effective measure for rock control of deep roadways.The developed hydraulic shields for 1000 m deep ultra-long working face can effectively improve the stability of surrounding rocks and mining efficiency in the longwall face.The ground control challenges in deep underground coal mines in China are discussed,and further research is recommended in terms of theory and technology for ground control in deep roadways and longwall faces.
基金supported by the National Natural Science Foundation of China(grant number 51805086)the Natural Science Foundation of Fujian Province,China(grant number 2018J01763)。
文摘To improve the defense capability of military equipment under extreme conditions,impact-resistant and high-energy-consuming materials have to be developed.The damping characteristic of entangled porous metallic wire materials(EPMWM)for vibration isolation was previously investigated.In this paper,a study focusing on the impact-resistance of EPMWM with the consideration of ambient temperature is presented.The quasi-static and low-velocity impact mechanical behavior of EPMWM under different temperatures(25℃-300℃)are systematically studied.The results of the static compression test show that the damping energy dissipation of EPMWM increases with temperature while the nonlinear damping characteristics are gradually enhanced.During the impact experiments,the impact energy loss rate of EPMWM was between 65%and 85%,while the temperatures increased from 25℃to 300℃.Moreover,under the same drop impact conditions,the overall deformation of EPMWM decreases in the temperature range of 100℃-200℃.On the other hand,the impact stiffness,energy dissipation,and impact loss factor of EPMWM significantly increase with temperature.This can be attributed to an increase in temperature,which changes the thermal expansion coefficient and contact state of the internal wire helixes.Consequently,the energy dissipation mode(dry friction,air damping,and plastic deformation)of EPMWM is also altered.Therefore,the EPMWM may act as a potential candidate material for superior energy absorption applications.
基金The project supported by the National Natural Science Foundation of China(10632080,10625208,10772027)
文摘One-stage light gas gun was utilized to study the dynamic mechanical properties of AD90 alumina subjected to the shock loading. Manganin gauges were adopted to obtain the stress-time histories. The velocity interferometer system for any reflector (VISAR) was used to obtain the free surface velocity profile and determine the Hugoniot elastic limit. The Hugoniot curves were fitted with the experimental data. From Hugoniot curves the compressive behaviors of AD90 alumina were found to change typically from elastic to "plastic". The dynamic mechanical behaviors for alumina under impact loadings were analyzed by using the path line principle of Lagrange analysis, including the nonlinear characteristics, the strain rate dependence, the dispersion and declination of shock wave in the material. A damage model applicable to ceramics subjected to dynamic compressive loading has been developed. The model was based on the damage micromechanics and wing crack nucleation and growth. The effects of parameters of both the micro-cracks nucleation and the initial crack size on the dynamic fracture strength were discussed. The results of the dynamic damage evolution model were compared with the experimental results and a good agreement was found.
文摘The mechanical behaviors and the microstructural characteristics of TC11 alloy with quenched martensite microstructure during hot compressive deformation were investigated. It shows that at various temperatures and strain rates, the stress strain curves firstly exhibit strain hardening, then strain softening and finally reach the steady deformation state; in the meanwhile, the initial lamellar microstructure is transformed into the equiaxed and uniform one through dynamic recrystallization. It shows that the present TC11 alloy has different Z D relationships in relatively lower temperature (RLT) range and relatively higher temperature (RHT) range, which is believed to be due to different deformation activation energies. During RHT deformation, dynamic recrystallization occurs in both α phases and β phases, but during RLT deformation, dynamic recrystallization only occurs in α phases and in the meanwhile β phases undergo a process of precipitation and growth.
文摘The ZrO2-Al2O3 ceramic composites were prepared by appropriate techniques with commercial ZrO2 and Al2O3 powders as raw materials and Y2O3 as stabilizer. The results indicate that with the introduction of Al2O3 into the ZrO2 matrix where the quantity of additive Y2O3 is 3.5% (mole fraction), the growth of ZrO2 grains is efficiently inhibited, which helps the ZrO2 grains exist in a metastable tetragonal manner; thus higher strength and toughness are acquired. When the content of alumina is 20% (mass fraction), the bending strength and fracture toughness of the composites are 676.7 MPa and 10 MPa·m1/2 respectively, the mechanical behaviors are close to those prepared with ZrO2 and Al2O3 powders synthesized through wet chemical approach. The mechanical behaviors of the composites are well improved owing to the dispersion toughening of alumina grains and phase transformation toughening of zirconia grains.
基金This work was supported by the National Natural Science Foundation of China under grant No.50075061.
文摘The basic mechanical behaviors of high density polyethylene electrofusion welded joint at different temperatures were studied by using differently designed specimens in this paper. The results show that the strength of weld bonding plane is higher than that of the pipe and socket materials at room temperature. In order to get the shear strength of electrofusion welded joint, the effective bond lengths were reduced by cutting artificial groove through the socket. The effective bonding length of welded joint to get the shear strength is decreased with decreasing testing temperature. The shear strength and the sensibility to sharp notch of HDPE material increased with decreasing temperature.
基金The work is supported by the National Natural Science Foundation of China(No.51578253)Scientific and Technological Planning Project of Xiamen City(Nos.3502Z20172011 and 3502Z20172014)+1 种基金Scientific and Technological Planning Project of Quanzhou City(No.2018C083R)Reform study of graduate education and teaching of Huaqiao University in 2018(No.18YJG55).
文摘The simplified mechanical model and finite element model are established on the basis of the measured results and analysis of the grouting pile deformation monitoring,surface horizontal displacement and vertical displacement monitoring,deep horizontal displacement(inclinometer)monitoring,soil pressure monitoring and seepage pressure monitoring in the lower reaches of Wuan River regulation project in Shishi,Fujian Province.The mechanical behavior and deformation performance of mould-bag pile retaining wall formed after controlled cement grouting in the silty stratum of the test section are analyzed and compared.The results show that the use of controlled cement grouting mould-bag pile technology is to strengthen the soft stratum for sealing water and reinforcement,so that it can rock into a retaining wall,which can both retain soil and seal water with excellent effect.The control of cement grouting technology not only makes the soft soil rock in the range of retaining wall of mould-bag pile,but also makes a wide range of soil around the mould-bag pile squeeze and embed to compaction;and its cohesion and internal friction angle increased,so as to achieve the purpose of reducing soil pressure and improving mechanical and deformation properties of retaining wall.
基金Sponsored by the National Natural Science Foundation of China(Grant Nos.10972200 and 11172270)
文摘In order to characterize the mechanical behaviors of the Velcro~? and Dual-lock fasteners, a series of tests including the butt-joint(BJ) monotonic tensile and shear, mixed tensile-shear with various loading angles, the loading rates effects, the double cantilever beam(DCB) fracture and 180° peel experiments were performed. The tensile and shear tests results showed that the mechanical behaviors of Velcro~? fastener separation are analogous to ductile materials, and those of Dual-lock fasteners are more like brittle ones. The mixed tensile-shear with various loading angles tests results demonstrated that magnitudes of the peak stresses in 30°, 45°, and 60° have no significant differences, which are lower than those in the monotonic tensile or shear tests for the two fasteners. The effects of the loading rate tests show that the peak stresses of the Velcro~? fastener manifested good performance at the loading rate of 10 to 20 mm/min in the tensile and shear conditions, and the Dual-lock did it well around the loading rates of 10 to 20 mm/min in the tensile condition. The cohesive zone model(CZM) is employed to numerical predict the DCB fracture and the 180° peel tests. The CZM predictions results are proven to commendably capture the two tests separation processes, of the tow fasteners, and the numerical results agreed well with the peeling tests data of the Dual lock fasteners. The results and discussions in this study are expected to bring more understanding to engineers and designers about the performance of Velcro~? and Dual lock fasteners.
文摘This Special Issue of the Journal of Rock Mechanics and GeotechnicalEngineering (JRMGE) contains 13 papers prepared by internationalexperts on various general topics in geomechanics, rockmechanics and geotechnical engineering. It represents a usefulmix of theoretical developments, testing and practical applications.We present in the following brief details in the papers, alphabeticallyin accordance with the last name of the first author.Barla presents a review of tunneling techniques with emphasison the full-face method combining full-face excavation and facereinforcement by means of fiber-glass elements with a yieldcontrolsupport. This method has been used successfully in difficultgeologic conditions, and for a wide spectrum of ground situations.The validation of the method with respect to the Saint Martin LaPorte access adit along the LyoneTurin Base tunnel experiencingseverely squeezing conditions during excavation is also includedin the paper. The numerical modeling with consideration of therock mass time-dependent behavior showed a satisfactory agreementwith monitoring results.
基金This project is sponsored by NNSFC(No.49775060).
文摘The hysteresis unit system was introduced to mechanical structure behavior of the TiNi SMA joint based on the structure characteristics of the martensite variants in the joints, and some functions reflecting its inner structure characteristics and micro-behavior such as density function, phase transformation function were set up from micro-points. Finally, the structure behavior relationship and corresponding mathematic model reflecting the relationship among hysteresis strain, stress and phase transformation strain were provided, which could predict the stress-strain behavior of the TiNi SMA joint to large extent.
基金Project supported by the Scientific and Technological Committee of Jiangsu Province (BG2002025)
文摘The effects of two types of additives, Y2O3 and Dy2O3, on the sintering and mechanical behaviors of AlN ceramics were investigated. The experimental results show that the sintering temperature can be decreased and the mechanical behavior can be improved by adding rare earth in AlN ceramics. The strength of AlN ceramics with Y2O3 and Dy2O3 are 326 and 320 MPa, respectively, which are 97.6% and 93.9% higher than the un-doped AlN ceramics. The fracture behavior on the fracture surfaces of rare earth oxide AlN ceramics was found to be a mixed mode of transgranular fracture and intergranular fracture. As a result, it is concluded that the improvement of bending strength of AlN ceramics with Y2O3 and Dy2O3 addition are mainly achieved by strengthening the grain boundary.
基金supported by the National Natural Science Foundation of China(Grant Nos.42171135 and 12262009)the“CUG Scholar”Scientific Research Funds at China University of Geosciences(Wuhan)(Project No.2022098).
文摘The phase equilibrium and mechanical behaviors of natural gas hydrate-bearing sediment are essential for gas recovery from hydrate reservoirs.In heating closed systems,the temperature-pressure path of hydrate-bearing sediment deviates from that of pure bulk hydrate,reflecting the porous media effect in phase equilibrium.A generalized phase equilibrium equation was established for hydrate-bearing sediments,which indicates that both capillary and osmotic pressures cause the phase equilibrium curve to shift leftward on the temperature-pressure plane.In contrast to bulk hydrate,hydrate-bearing sediment always contains a certain amount of unhydrated water,which keeps phase equilibrium with the hydrate within the hydrate stability field.With changes in temperature and pressure,a portion of pore hydrate and unhydrated water may transform into each other,affecting the shear strength of hydrate-bearing sediment.A shear strength model is proposed to consider not only hydrate saturation but also the change in temperature and pressure of hydrate-bearing sediment.The model is validated by experimental data with various hydrate saturation,temperature and pressure conditions.The deformation induced by partial dissociation was studied through depressurization tests under constant effective stress.The reduction in gas pressure within the hydrate stability field indeed caused sediment deformation.The dissociation-induced deformation can be reasonably estimated as the difference in volume between hydrate-bearing and hydrate-free sediments from the compression curves.
基金supported by the National Natural Science Foundation of China(No.52275310)the Open Project of State Key Laboratory of Explosion Science and Technology(No.QNKT22-15)the characterization at the Analysis&Testing Center,Beijing Institute of Technology.
文摘Precursor-derived ceramic SiOC(PDC-SiOC)microlattices exhibit excellent oxidation resistance,high-temperature stability,and superior mechanical properties.However,the printing accuracy of the PDC-SiOC microlattices by 3D printing is still limited,and mechanical properties of the PDC-SiOC microlattices have not been studied systematically.Here,PDC-SiOC octet microlattices were fabricated by projection micro stereolithography(PμSL)3D printing,and photoabsorber(Sudan III)’s effect on the accuracy was systematically analyzed.The results showed that the addition of Sudan III improved the printing accuracy significantly.Then,the ceramization process of the green body was analyzed in detail.The order of the green body decreased,and most of their chemical bonds were broken during pyrolysis.After that,the PDC-SiOC microlattices with different truss diameters in the range of 52–220μm were fabricated,and their mechanical properties were investigated.The PDC-SiOC microlattices with a truss diameter of 52μm exhibited higher compression strength(31 MPa)than those with bigger truss diameters.The size effect among the PDC-SiOC microlattices was analyzed.Our work provides a deeper insight into the manufacturing of PDC-SiOC micro-scaled architectures by 3D printing and paves a path to the research of the size effect in ceramic structures.
基金supported by the National Natural Science Foundation of China(Nos.42090054,41922055 and 41931295)the Research Project of China Three Gorges Corporation(No.2019073)+1 种基金the Zhejiang Huadong Construction Engineering Co.,Ltd.(No.KY2019-HDJS-07)the Key Research and Development Program of Hubei Province of China(No.2022CFA002)。
文摘Rock bolts are widely employed as an effective and efficient reinforcement method in geotechnical engineering.Sandwich composite structures formed by hard rock and weak rock are often encountered in practical projects.Furthermore,the spatial structure of the rock mass has a direct influence on the effect of the anchorage support.To investigate the impact of rock mass structure on the mechanical characteristics of anchorage interfaces,pull-out tests on reinforced specimens with different mudstone thicknesses and fracture dip angles are conducted.The experimental results indicate that the percentage of mudstone content and fracture dip angle have a significant influence on the pullout load of the samples.A weaker surrounding rock results in a lower peak load and a longer critical anchorage length,and vice versa.The results also show that 70%mudstone content can be considered a critical condition for impacting the peak load.Specifically,the percentage of mudstone content has a limited influence on the variation in the peak load when it exceeds 70%.Optical fiber deformation results show that compared to the rock mass with fracture dip angles of 0°and 60°,the rock mass with a fracture dip angle of 30°has a more uniformly distributed force at the anchorage interface.When the fracture dip angle exceeds 60°,the dip angle is no longer a key indicator of peak load.The accuracy of the experimentally obtained load-displacement curves is further verified although numerical simulation using the discrete element method.
基金financially supported by the National Natural Science Foundation of China(Nos.12272356,12072326,and 12172337)the State Key Laboratory of Dynamic Measurement Technology,North University of China(No.2022-SYSJJ-03)。
文摘Al Si10Mg porous protective structure often produces different damage forms under compressive loading,and these damage modes affect its protective function.In order to well meet the service requirements,there is an urgent need to comprehensively understand the mechanical behavior and response mechanism of AlSi10Mg porous structures under compressive loading.In this paper,Al Si10Mg porous structures with three kinds of volume fractions are designed and optimized to meet the requirements of high-impact,strong-energy absorption,and lightweight characteristics.The mechanical behaviors of AlSi10Mg porous structures,including the stress-strain relationship,structural bearing state,deformation and damage modes,and energy absorption characteristics,were obtained through experimental studies at different loading rates.The damage pattern of the damage section indicates that AlSi10Mg porous structures have both ductile and brittle mechanical properties.Numerical simulation studies show that the AlSi10Mg porous structure undergoes shear damage due to relative misalignment along the diagonal cross-section,and the damage location is almost at 45°to the load direction,which is the most direct cause of its structural damage,revealing the damage mechanism of AlSi10Mg porous structures under the compressive load.The normalized energy absorption model constructed in the paper well interprets the energy absorption state of Al Si10Mg porous structures and gives the sensitive location of the structures,and the results of this paper provide important references for peers in structural design and optimization.
基金This work is financially supported by the National Natural Science Foundation of China(Grants 11772268,11527803,11832015 and 11627901)the National Key R&D Program of China(Grant 2017YFB1103500)the 111 Project(Grant BP0719007).The authors also thanks for Dr.Yinggang Miao for useful discussions.
文摘Full understanding of the thermomechanical behaviors of materials at high strain rates and high temperatures are of great importance from not only scientific meaning but also practical value in engineering structure design and safety assessment.Great efforts have been made for abilities of operation the split Hopkinson bars,the most popular technique for experimental determination of mechanical behaviors of materials over the strain rates from 10^2 to 10^4 s^−1 over the past 70 years,at high temperatures since 1960s.A review of experiment work is presented in this paper to give an overview of the development of experimental techniques at high temperatures based on Hopkinson bar systems.The principles of the split Hopkinson bar requires the loading bars avoiding temperature gradient or keeping relatively low temperature when performing high temperature testing.Techniques such as performing temperature gradient corrections,rapid heating or using special designed automatically assembled systems were proposed by researchers to enable the operation of the split Hopkinson bars at temperature as high as possible.Moreover,to the application of high speed photographic technique for capturing the dynamic deformation process of the specimen in high temperature Hopkinson bar testing,some key issues of eliminating the strong thermal radiation induced lights oversaturation and de-blurring of images due to insufficient exposure at high temperature and high strain rate condition,as well as fabrication of high contrast speckle pattern for high temperature digital image correlation measurement were also proposed.The technique can now enable the split Hopkinson bar testing to be performed at high temperature up to 1873 K under the loading conditions of compression or tension with the in situ observation and full field measurement of deformation as well.The paper concludes with summaries of the most important achievements and highlighting of the prospects,trends and remaining challenges for future research.
基金supported by the National Natural Science Foundation of China(Grant No.51332003,No.11572057 and No.11702037)Program for Changjiang Scholars and Innovative Research Team(IRT14R37).
文摘In this work,we present a new piezoelectric solid solution consisting of two typical alkali niobate-based materials,K_(0.5)Na_(0.5)NbO_(3)(KNN)and Li_(0.15)Na_(0.85)NbO_(3)(LNN).Although KNN and LNN have the same perovskite structure,they exhibit extremely different electrical properties and mechanical behaviors.The phase structures,electrical and mechanical evolutions of the new lead-free piezoelectric materials with different ratios of KNN and LNN are comprehensively and theoretically investigated.According to the Xray diffraction patterns and curves of permittivity versus temperature,a series of complicated phase transitions can be found with varied LNN content.Rietveld refinement results based on XRD patterns reveal an oxygen octahedron tilting in the LNN-rich crystal structure,and simultaneously the reasons for octahedron tilting are discussed.The distorted crystal structure is accompanied by extremely decreased electric properties but increased mechanical properties,which reveals electrical and mechanical properties of alkali niobate-based piezoelectric ceramics strongly depend on their inner structures,and the enhancement of intrinsic hardness results in the deterioration of piezoelectric properties.Our work exhibits the detailed evolutions of structure,electrical and mechanical properties from KNN to LNN,which provides experimental and theoretical basis for development of new alkali niobate-based piezoelectric materials.
基金The authors are grateful for the support from the National Natural Science Foundation of China(Grants 11820101001,11572236 and 11372236)the Natural Science Foundation of Shaanxi Province(Grant 2020JQ-010)the State Key Laboratory of Nonlinear Mechanics.
文摘Current constitutive theories face challenges when predicting the extremely large deformation and fracture of hydrogels,which calls for the demands to reveal the fundamental mechanism of the various mechanical behaviors of hydrogels from bottom up.Proper hydrogel network model provides a better approach to bridge the gap between the micro-structure and the macroscopic mechanical responses.This work summarizes the theoretical and numerical researches on the hydrogel network models,aiming to provide new insights into the effect of microstructure on the swelling-deswelling process,hyperelasticity,viscoelasticity and fracture of hydrogels.Hydrogel network models are divided into full-atom network models,realistic network models and abstract network models.Full-atom network models have detailed atomic structure but small size.Realistic network models with different coarse-graining degree have large model size to explain the swelling-deswelling process,hyperelasticity and viscoelasticity.Abstract network models abstract polymer chains into analytical interactions,leading to the great leap of model size.It shows advantages to reproduce the crack initiation and propagation in hydrogels by simulating chain scission.Further research directions on the network modeling are suggested.We hope this work can help integrate the merits of network modeling methods and continuum mechanics to capture the various mechanical behaviors of hydrogels.
基金This research is supported by Scientific Research Starting Project of SWPU(No.2017QHZ012)Major Project by Education Office of Sichuan Province(No.17ZA0418)+1 种基金supported by the Natural Science Fund for Outstanding Youth Science Fund(Grant No.51222406)Scientific Research Innovation Team Project of Sichuan Colleges and Universities(2017TD0014).
文摘Double shoulder drill pipe joint(DSJ)is a novel thread structure which appears in recent years.Its strength reduced efficiently while the structure design is not appropriately,for the DSJ’s mechanical behaviors weren’t well studied.In this paper a 3D whole structure finite element model of DSJ was established based on the Principle of Virtual Work,and validated the model’s computing results by experimental results.The authors analyzed the stress and strain distribution with the 3D whole structure finite element model’s computing results under torque moment,compression force,tension load,and bend moment.And then acquired the DSJ’s mechanical behaviors under each load.The research works of this paper refer accordance to recognize and design the DSJ.