Elastic moduli,e.g.shear modulus G and bulk modulus K,are important parameters of geotechnical materials,which are not only the indices for the evaluation of the deformation ability of soils but also the important bas...Elastic moduli,e.g.shear modulus G and bulk modulus K,are important parameters of geotechnical materials,which are not only the indices for the evaluation of the deformation ability of soils but also the important basic parameters for the development of the constitutive models of geotechnical materials.In this study,a series of triaxial loading-unloading-reloading shear tests and isotropic loading-unloadingreloading tests are conducted to study several typical mechanical properties of coral calcareous sand(CCS),and the void ratio evolution during loading,unloading and reloading.The test results show that the stress-strain curves during multiple unloading processes are almost parallel,and their slopes are much greater than the deformation modulus at the initial stage of loading.The relationship between the confining pressure and the volumetric strain can be defined approximately by a hyperbolic equation under the condition of monotonic loading of confining pressure.Under the condition of confining pressure unloading,the evolution of void ratio is linear in the e-lnp0 plane,and these lines are a series of almost parallel lines if there are multiple processes of unloading.Based on the experimental results,it is found that the modified Hardin formulae for the elastic modulus estimation have a significant deviation from the tested values for CCS.Based on the experimental results,it is proposed that the elastic modulus of soils should be determined by the intersection line of two spatial surfaces in the G/K-e-p’/pa space(pa:atmosphere pressure).“Ye formulation”is further proposed for the estimation of the elastic modulus of CCS.This new estimation formulation for soil elastic modulus would provide a new method to accurately describe the mechanical behavior of granular soils.展开更多
In nature,there are widely distributed bi-modulus materials with different deformation characteristics under compressive and tensile stress states,such as concrete,rock and ceramics.Due to the lack of constitutive mod...In nature,there are widely distributed bi-modulus materials with different deformation characteristics under compressive and tensile stress states,such as concrete,rock and ceramics.Due to the lack of constitutive model that could reasonably consider the bi-modulus property of materials,and the lack of simple and reliable measurement methods for the tensile elastic parameters of materials,scientists and engineers always neglect the effect of the bi-modulus property of materials in engineering design and numerical simulation.To solve this problem,this study utilizes the uncoupled strain-driven constitutive model proposed by Latorre and Montáns(2020)to systematically study the distributions and magnitudes of stresses and strains of bi-modulus materials in the three-point bending test through the numerical method.Furthermore,a new method to synchronously measure the tensile and compressive elastic moduli of materials through the four-point bending test is proposed.The numerical results show that the bi-modulus property of materials has a significant effect on the stress,strain and displacement in the specimen utilized in the three-point and four-point bending tests.Meanwhile,the results from the numerical tests,in which the elastic constitutive model proposed by Latorre and Montáns(2020)is utilized,also indicate that the newly proposed measurement method has a good reliability.Although the new measurement method proposed in this study can synchronously and effectively measure the tensile and compressive elastic moduli,it cannot measure the tensile and compressive Poisson’s ratios.展开更多
Three-dimensional(3D)bioprinting has been used widely for the construction of hard tissues such as bone and cartilage.However,constructing soft tissues with complex structures remains a challenge.In this study,complex...Three-dimensional(3D)bioprinting has been used widely for the construction of hard tissues such as bone and cartilage.However,constructing soft tissues with complex structures remains a challenge.In this study,complex structures characterized by both tunable elastic modulus and porosity were printed using freeform reversible embedding of suspended hydrogels(FRESHs)printing methods.A mixture of alginate and gelatin was used as the main functional component of the bioink.Rheological analysis showed that this bioink possesses shear thinning and shear recovery properties,supporting both cryogenic and FRESH printing methods.Potential printing capabilities and limitations of cryogenic and FRESH printing were then analyzed by printability tests.A series of complex structures were printed by FRESH printing methods which could not be realized using conventional approaches.Mechanical tests and scanning electron microscopy analysis showed that the printed structure is of excellent flexibility and could be applied in various conditions by adjusting its mechanical modulus and porosity.L929 fibroblast cells maintained cell viability in cell-laden-printed structures,and the addition of collagen further improved the hydrogels’biocompatibility.Overall,all results provided useful insight into the building of human soft tissue organ blocks.展开更多
The bamboo scrimber is an anisotropic material.The elastic constant values of the bamboo scrimber specimens measured by the dynamic and static methods are consistent,and the dynamic test method has the advantages of r...The bamboo scrimber is an anisotropic material.The elastic constant values of the bamboo scrimber specimens measured by the dynamic and static methods are consistent,and the dynamic test method has the advantages of rapidity,simplicity,good repeatability,and high precision.Bamboo scrimber has strong potential as a building material,and its elastic constant is an important index to measure its mechanical properties.To quickly,simply,non-destructively,and accurately detect the elastic constant of the bamboo scrimber,they were dynamically tested by the free plate transient excitation method and cantilever plate torsional vibration method.The static four-point bending method was used to verify the accuracy and reliability of the dynamic elastic modulus,shear modulus,and Poisson’s ratio of the bamboo scrimber.The mechanism analysis and evaluation of the quality grade,homogeneity,and size effect of the bamboo scrimber whole board were carried out.The main results show that the dynamic elastic modulus,shear modulus,and Poisson’s ratio of the bamboo scrimber are 12 GPa,1500 MPa,and 0.31,respectively,which meet the requirements of GB/T 40247-2021 for structural bamboo scrimber.展开更多
The equivalent elastic modulus is a parameter for controlling the deformation behavior of fractured rock masses in the equivalent continuum approach.The confining stress,whose effect on the equivalent elastic modulus ...The equivalent elastic modulus is a parameter for controlling the deformation behavior of fractured rock masses in the equivalent continuum approach.The confining stress,whose effect on the equivalent elastic modulus is of great importance,is the fundamental stress environment of natural rock masses.This paper employs an analytical approach to obtain the equivalent elastic modulus of fractured rock masses containing random discrete fractures(RDFs)or regular fracture sets(RFSs)while considering the confining stress.The proposed analytical solution considers not only the elastic properties of the intact rocks and fractures,but also the geometrical structure of the fractures and the confining stress.The performance of the analytical solution is verified by comparing it with the results of numerical tests obtained using the three-dimensional distinct element code(3DEC),leading to a reasonably good agreement.The analytical solution quantitatively demonstrates that the equivalent elastic modulus increases substantially with an increase in confining stress,i.e.it is characterized by stress-dependency.Further,a sensitivity analysis of the variables in the analytical solution is conducted using a global sensitivity analysis approach,i.e.the extended Fourier amplitude sensitivity test(EFAST).The variations in the sensitivity indices for different ranges and distribution types of the variables are investigated.The results provide an in-depth understanding of the influence of the variables on the equivalent elastic modulus from different perspectives.展开更多
The relationship between the plane-orientation function and the space-orientation function of whiskers in whisker-reinforced metal matrix composites was analyzed theoretically. The actual orientation of whiskers in th...The relationship between the plane-orientation function and the space-orientation function of whiskers in whisker-reinforced metal matrix composites was analyzed theoretically. The actual orientation of whiskers in the as- cast 20%SiC_W/Mg composite (SiC_W content in volume fraction) were investigated, and the elastic modulus of the composite was measured with an ultrasonic velocity analyzer. Results show that there is an evident difference be- tween the plane-orientation function and the space-orientation function of whiskers and the space-orientation function can represent the actual condition of the composite. Only by using the space-orientation function of whiskers, the difference of elastic modulus of the as-cast composite in different directions can be explained reasonably.展开更多
Elastic modulus(E)interpretation is debatable with limited literature detailing the impact of systemcompliance.To address this impact,a comprehensive testing schedule using an aluminium 6061(Al)sample is carried out o...Elastic modulus(E)interpretation is debatable with limited literature detailing the impact of systemcompliance.To address this impact,a comprehensive testing schedule using an aluminium 6061(Al)sample is carried out on several systems under various test setups.Al is chosen as it is extruded and adheres to well defined shape tolerances and elastic properties.A robust method,using the Savitzky-Golay filter,is introduced to identify significant slope changes in the stressestrain curve.Since the load in the test system is well defined,the recorded deformation is corrected to the expected value of Al resulting in a system-compliance factor.The results across the testing systems and test setups showed significant variance,with the recorded E always lower than the anticipated EAl.The number of components within the system over which the deformation is measured had the most significant impact,lowering the expected E by up to 50%.Additionally,the system-compliance factor is inconsistent across different systems and setups.Thus,it is evidently proved that each setup must be separately evaluated for its system-compliance and that no single value exists across systems and setups.The findings are then projected onto a series of uniaxial compressive strength(UCS)tests carried out on Stanstead granite(SS GR)samples.The corrected Et50 and Eavg values for system-compliance of the samples are within1%for each system as opposed to being50%pre-correction.The findings conclude that it is deemed necessary and of utmost importance that the deformation be corrected to accommodate the systemcompliance to obtain reliable results.展开更多
By using the system of image analyzer connected with scanning electron microscope, the whisker orientation in the SiC w/6061Al alloy composite as squeeze cast was measured. According to the shear lag model and the act...By using the system of image analyzer connected with scanning electron microscope, the whisker orientation in the SiC w/6061Al alloy composite as squeeze cast was measured. According to the shear lag model and the actual distribution function of whisker in composite, the inhomogeneity of elastic modulus in composite was analyzed. With the method of ultrasonic velocity, the elastic modulus of composite was measured. The results showed that, the whiskers of composite are preferred in an orientation normal to the direction of squeeze cast. The higher the volume fraction of whisker, the more extent of preferred orientation of it, and the inhomogeneity of elastic modulus is mainly due to the differences of whisker distribution in composite.展开更多
Based on the experimental and theoretical analysis, the tensile elastic modulus, strength and fracture characteristics of squeeze casting δ-Al2O3/Al alloy composites were studied. The fracture characteristics of comp...Based on the experimental and theoretical analysis, the tensile elastic modulus, strength and fracture characteristics of squeeze casting δ-Al2O3/Al alloy composites were studied. The fracture characteristics of composites were observed by SEM. The elastic modulus was predicted by the finite element method based on the energy equivalence principle, and the strength was predicted by the statistical integration average method using the maximum energy criterion of composite strength. In the prediction, the distribution density functions of the fiber’s. orientation and length were considered. These functions were gained by experimental measurement. It is shown that the predicted results are in agreement with the experimental values well and the microstructure feature of composites controls the fracture characteristics.展开更多
Toarcian claystone such as that of the Callovo-Oxfordian is a qualified multiphase material. The claystone samples tested in this study are composed of four main mineral phases: silicates(clay minerals, quartz,feldspa...Toarcian claystone such as that of the Callovo-Oxfordian is a qualified multiphase material. The claystone samples tested in this study are composed of four main mineral phases: silicates(clay minerals, quartz,feldspars, micas)(z86%), sulphides(pyrite)(z3%), carbonates(calcite, dolomite)(z10%) and organic kerogen(z1%). Three sets of measurements of the modulus of deformability were compared as determined in(i) nanoindentation tests with a constant indentation depth of 2 mm,(ii) micro-indentation tests with a constant indentation depth of 20 mm, and(iii) meso-compression tests with a constant displacement of 200 mm. These three experimental methods have already been validated in earlier studies. The main objective of this study is to demonstrate the influence of the scaling effect on the modulus of deformability of the material. Different frequency distributions of the modulus of deformability were obtained at the different sample scales:(i) in nano-indentation tests, the distribution was spread between 15 GPa and 90 GPa and contained one peak at34 GPa and another at 51 GPa;(ii) in the micro-indentation tests, the distribution was spread between 25 GPa and 60 GPa and displayed peaks at 26 GPa and 37 GPa; and(iii) in the meso-compression tests, a narrow frequency distribution was obtained, ranging from 25 GPa to 50 GPa and with a maximum at around 35 GPa.展开更多
Rock properties exhibit spatial variabilities due to complex geological processes such as sedimentation,metamorphism, weathering, and tectogenesis. Although recognized as an important factor controlling the safety of ...Rock properties exhibit spatial variabilities due to complex geological processes such as sedimentation,metamorphism, weathering, and tectogenesis. Although recognized as an important factor controlling the safety of geotechnical structures in rock engineering, the spatial variability of rock properties is rarely quantified. Hence, this study characterizes the autocorrelation structures and scales of fluctuation of two important parameters of intact rocks, i.e. uniaxial compressive strength(UCS) and elastic modulus(EM).UCS and EM data for sedimentary and igneous rocks are collected. The autocorrelation structures are selected using a Bayesian model class selection approach and the scales of fluctuation for these two parameters are estimated using a Bayesian updating method. The results show that the autocorrelation structures for UCS and EM could be best described by a single exponential autocorrelation function. The scales of fluctuation for UCS and EM respectively range from 0.3 m to 8.0 m and from 0.3 m to 8.4 m.These results serve as guidelines for selecting proper autocorrelation functions and autocorrelation distances for rock properties in reliability analyses and could also be used as prior information for quantifying the spatial variability of rock properties in a Bayesian framework.展开更多
The mismatch of elasticity modulus has limited the application of titanium alloys in medical implants,and porous structures have been proved effective to deal with this problem. However,the manufacturing of porous str...The mismatch of elasticity modulus has limited the application of titanium alloys in medical implants,and porous structures have been proved effective to deal with this problem. However,the manufacturing of porous structures has been restricted from conventional technologies. In this study,selective laser melting( SLM) technology was employed to produce a set of Ti-6Al-4V porous samples based on cubic lattices with varying size of strut width from 200 μm to 600 μm. Then the compression tests were conducted to analyze the influence of the strut width on the elasticity modulus and the ultimate strength. The result shows both of them increases linearly with the growth of strut width or with the decrease of porosity,and the elasticity modulus of porous parts is largely reduced and actually meets the requirement of clinical application. Additionally,a finite element model was established to verify the un-uniform stress distribution of porous parts. It reveals that fractures always initially occur at the vertical struts along the force direction which suffer from the main deformation.展开更多
Internal friction and elastic modulus of ternary Mn-Cu-Al alloys containing 56—60wt-% Mn,0-3.59 wt-% Al were measured with acoustic frequency,1 kHz,in the tempera-ture range of-150 to 150℃.It was found that when the...Internal friction and elastic modulus of ternary Mn-Cu-Al alloys containing 56—60wt-% Mn,0-3.59 wt-% Al were measured with acoustic frequency,1 kHz,in the tempera-ture range of-150 to 150℃.It was found that when the specimen was aged in the temperaturerange under the spinodal curve within the miscibility gap(400—500℃),the internal fric-tion increases with an increase of the aging time and reaches a maximum value at a certain ag-ing time which is shorter with a higher aging temperature.Two internal friction peaks whichdid not appear before the aging were observed above room temperature after a definite agingtime.These are respectively the martensitic tranformation peak and the relaxation peak orig-inating from the stress-induced movement of the twin boundaries.The former peak shifts to-ward higher temperatures with an increase of the aging time,whereas the relaxation peak ap-pearing at 15℃,is independent of the aging time and temperature.The activation energy as-sociated with the relaxation peak was found to be 0.56 eV which is about the same as that ofthe relaxation peak in binary alloy containing 90 wt-% Mn.It was also found that thehardness,strength and the brittleness of the specimen increase when aged below the spinodalcurve within the miscibility gap.The addition or Al enhances the strength but reduces the in-ternal friction of the specimen.A choice of suitable aging time and temperature can give anoptimum compromise of high strength and high internal friction.Analysis of experimental re-sults suggests that spinodal decomposition leads to Mn-rich zones in the specimen and thuscauses the phase transformation and the change of mechanical properties of the specimen.展开更多
A new strategy for elastic modulus adjustment is proposed based on the element bearing ratio (EBR),and the elastic modulus reduction method (EMRM) is proposed for limit load evaluation of frame structures. The EBR is ...A new strategy for elastic modulus adjustment is proposed based on the element bearing ratio (EBR),and the elastic modulus reduction method (EMRM) is proposed for limit load evaluation of frame structures. The EBR is defined employing the generalized yield criterion,and the reference EBR is determined by introducing the extrema and the degree of uniformity of EBR in the structure. The elastic modulus in the element with an EBR greater than the reference one is reduced based on the linear elastic finite element analysis and the equilibrium of strain energy. The lower-bound of limit-loads of frame structures are analyzed and the numerical example demonstrates the flexibility,accuracy and effciency of the proposed method.展开更多
Two semi-empirical approaches for prediction of elastic modulus of biphasic composites have been proposed. Developed relations are for pore free matrix and pore free filler and found to depend on nonlinear contributio...Two semi-empirical approaches for prediction of elastic modulus of biphasic composites have been proposed. Developed relations are for pore free matrix and pore free filler and found to depend on nonlinear contribution of volume fraction of constituents as well as ratio of elastic properties of individual phases. These relations are applied for the calculation of effective elastic modulus mainly for Al2O3-NiAl, SiC-Al, Alumina-Zirconia, Al-Al2O3, W-glass and Flax-Resin composite materials. Theoretical predictions using developed relations are compared with experimental data. It is found that the predicted values of effective elastic modulus using modified relations are quite close to the experimental results.展开更多
The size-dependent elastic property of rectangular nanobeams(nanowires or nanoplates) induced by the surface elasticity effect is investigated by using a developed modified core-shell model.The effect of surface elast...The size-dependent elastic property of rectangular nanobeams(nanowires or nanoplates) induced by the surface elasticity effect is investigated by using a developed modified core-shell model.The effect of surface elasticity on the elastic modulus of nanobeams can be characterized by two surface related parameters,i.e.,inhomogeneous degree constant and surface layer thickness.The analytical results show that the elastic modulus of the rectangular nanobeam exhibits a distinct size effect when its characteristic size reduces below 100 nm.It is also found that the theoretical results calculated by a modified core-shell model have more obvious advantages than those by other models(core-shell model and core-surface model)by comparing them with relevant experimental measurements and computational results,especially when the dimensions of nanostructures reduce to a few tens of nanometers.展开更多
The four point bending method was applied to measure X ray elastic constants(XEC) of (422) and (331) planes of TiN coating. Elastic Modulus and XECs of all the crystal planes were calculated by Kroner method. The resu...The four point bending method was applied to measure X ray elastic constants(XEC) of (422) and (331) planes of TiN coating. Elastic Modulus and XECs of all the crystal planes were calculated by Kroner method. The results from the calculation and the experiment were compared. It is concluded that the XECs values of same film prepared by different techniques scatter a little because of the effects of stoichiometric proportion and microstructure of films. [展开更多
The distribution and magnitude of surface and subsurface stresses of the single-layer sprayed-coatings on monolithic substrates were investigated by finite element method(FEM) .The models of coating configurations wit...The distribution and magnitude of surface and subsurface stresses of the single-layer sprayed-coatings on monolithic substrates were investigated by finite element method(FEM) .The models of coating configurations with different thicknesses and elastic modulus ratios of coating to substrate were introduced,and the effects of thickness and elastic modulus ratio on the stresses were addressed.The calculation results show that the coating/substrate interface shear stress obviously decreases with increasing coating thickness,due to the location of the maximum shear stress moving away from the coating/substrate interface.At the same time,the magnitude of von Mises stress also declines in the case of thicker coatings.However,the high elastic modulus ratio results in extremely high maximum shear stress and the severe discontinuity of the von Mises stress curves,which leads to the intensive stress concentration on the coating/substrate interface.So the coating configurations with the larger coating thickness and lower difference of elastic modulus between coating and substrate exhibit excellent resistant performance of rolling contact fatigue(RCF).展开更多
Based on the Hertzian granular contact mechanics model, the paper built up a Macroscopic Young’s Elastic Modulus of particle/granular packing rock layers, and built up a ties to connecting Young’s Elastic Modulus of...Based on the Hertzian granular contact mechanics model, the paper built up a Macroscopic Young’s Elastic Modulus of particle/granular packing rock layers, and built up a ties to connecting Young’s Elastic Modulus of sand particle in Meso and the Macroscopic Young’s Modulus of granular packing rock layers. The Macroscopic Young’s Modulus of granular packing rock layers is far less than the Young’s Modulus of sand particle. The Macroscopic Young’s Modulus of granular packing rock layers is proportioned to the powers of 1/3 of the vertical contact force of sand particles. The Macroscopic Young’s Modulus is inversely proportional to particle diameter. The paper calculated the vertical contact force of five types aligning mode of the particles. When equal stress, the increased of the coordination number lead to the decrease of the contact force fn, this lead to the coordination number is an inverse proportion to Macroscopic Young’s Modulus. But the larger coordination number change only means very little Macroscopic Young’s Modulus change.展开更多
基金Professor Jianhong Ye is grateful for the funding support from the National Key Research and Development Program of China(Grant No.2022YFC3102402).
文摘Elastic moduli,e.g.shear modulus G and bulk modulus K,are important parameters of geotechnical materials,which are not only the indices for the evaluation of the deformation ability of soils but also the important basic parameters for the development of the constitutive models of geotechnical materials.In this study,a series of triaxial loading-unloading-reloading shear tests and isotropic loading-unloadingreloading tests are conducted to study several typical mechanical properties of coral calcareous sand(CCS),and the void ratio evolution during loading,unloading and reloading.The test results show that the stress-strain curves during multiple unloading processes are almost parallel,and their slopes are much greater than the deformation modulus at the initial stage of loading.The relationship between the confining pressure and the volumetric strain can be defined approximately by a hyperbolic equation under the condition of monotonic loading of confining pressure.Under the condition of confining pressure unloading,the evolution of void ratio is linear in the e-lnp0 plane,and these lines are a series of almost parallel lines if there are multiple processes of unloading.Based on the experimental results,it is found that the modified Hardin formulae for the elastic modulus estimation have a significant deviation from the tested values for CCS.Based on the experimental results,it is proposed that the elastic modulus of soils should be determined by the intersection line of two spatial surfaces in the G/K-e-p’/pa space(pa:atmosphere pressure).“Ye formulation”is further proposed for the estimation of the elastic modulus of CCS.This new estimation formulation for soil elastic modulus would provide a new method to accurately describe the mechanical behavior of granular soils.
基金funding support from the National Key Research and Development Program of China(Grant No.2022YFC3102402)as well as from the National Natural Science Foundation of China(Grant No.51879257).
文摘In nature,there are widely distributed bi-modulus materials with different deformation characteristics under compressive and tensile stress states,such as concrete,rock and ceramics.Due to the lack of constitutive model that could reasonably consider the bi-modulus property of materials,and the lack of simple and reliable measurement methods for the tensile elastic parameters of materials,scientists and engineers always neglect the effect of the bi-modulus property of materials in engineering design and numerical simulation.To solve this problem,this study utilizes the uncoupled strain-driven constitutive model proposed by Latorre and Montáns(2020)to systematically study the distributions and magnitudes of stresses and strains of bi-modulus materials in the three-point bending test through the numerical method.Furthermore,a new method to synchronously measure the tensile and compressive elastic moduli of materials through the four-point bending test is proposed.The numerical results show that the bi-modulus property of materials has a significant effect on the stress,strain and displacement in the specimen utilized in the three-point and four-point bending tests.Meanwhile,the results from the numerical tests,in which the elastic constitutive model proposed by Latorre and Montáns(2020)is utilized,also indicate that the newly proposed measurement method has a good reliability.Although the new measurement method proposed in this study can synchronously and effectively measure the tensile and compressive elastic moduli,it cannot measure the tensile and compressive Poisson’s ratios.
基金supported by the National Natural Science Foundation of China(Nos.52275464 and 52075300)the Scientific Research Project for National High-Level Innovative Talents ofHebei Province Full-Time Introduction(No.2021HBQZYCXY004).
文摘Three-dimensional(3D)bioprinting has been used widely for the construction of hard tissues such as bone and cartilage.However,constructing soft tissues with complex structures remains a challenge.In this study,complex structures characterized by both tunable elastic modulus and porosity were printed using freeform reversible embedding of suspended hydrogels(FRESHs)printing methods.A mixture of alginate and gelatin was used as the main functional component of the bioink.Rheological analysis showed that this bioink possesses shear thinning and shear recovery properties,supporting both cryogenic and FRESH printing methods.Potential printing capabilities and limitations of cryogenic and FRESH printing were then analyzed by printability tests.A series of complex structures were printed by FRESH printing methods which could not be realized using conventional approaches.Mechanical tests and scanning electron microscopy analysis showed that the printed structure is of excellent flexibility and could be applied in various conditions by adjusting its mechanical modulus and porosity.L929 fibroblast cells maintained cell viability in cell-laden-printed structures,and the addition of collagen further improved the hydrogels’biocompatibility.Overall,all results provided useful insight into the building of human soft tissue organ blocks.
文摘The bamboo scrimber is an anisotropic material.The elastic constant values of the bamboo scrimber specimens measured by the dynamic and static methods are consistent,and the dynamic test method has the advantages of rapidity,simplicity,good repeatability,and high precision.Bamboo scrimber has strong potential as a building material,and its elastic constant is an important index to measure its mechanical properties.To quickly,simply,non-destructively,and accurately detect the elastic constant of the bamboo scrimber,they were dynamically tested by the free plate transient excitation method and cantilever plate torsional vibration method.The static four-point bending method was used to verify the accuracy and reliability of the dynamic elastic modulus,shear modulus,and Poisson’s ratio of the bamboo scrimber.The mechanism analysis and evaluation of the quality grade,homogeneity,and size effect of the bamboo scrimber whole board were carried out.The main results show that the dynamic elastic modulus,shear modulus,and Poisson’s ratio of the bamboo scrimber are 12 GPa,1500 MPa,and 0.31,respectively,which meet the requirements of GB/T 40247-2021 for structural bamboo scrimber.
基金financially supported by the National Nature Science Foundation of China (Grant Nos. 42022053 and 41877220)
文摘The equivalent elastic modulus is a parameter for controlling the deformation behavior of fractured rock masses in the equivalent continuum approach.The confining stress,whose effect on the equivalent elastic modulus is of great importance,is the fundamental stress environment of natural rock masses.This paper employs an analytical approach to obtain the equivalent elastic modulus of fractured rock masses containing random discrete fractures(RDFs)or regular fracture sets(RFSs)while considering the confining stress.The proposed analytical solution considers not only the elastic properties of the intact rocks and fractures,but also the geometrical structure of the fractures and the confining stress.The performance of the analytical solution is verified by comparing it with the results of numerical tests obtained using the three-dimensional distinct element code(3DEC),leading to a reasonably good agreement.The analytical solution quantitatively demonstrates that the equivalent elastic modulus increases substantially with an increase in confining stress,i.e.it is characterized by stress-dependency.Further,a sensitivity analysis of the variables in the analytical solution is conducted using a global sensitivity analysis approach,i.e.the extended Fourier amplitude sensitivity test(EFAST).The variations in the sensitivity indices for different ranges and distribution types of the variables are investigated.The results provide an in-depth understanding of the influence of the variables on the equivalent elastic modulus from different perspectives.
文摘The relationship between the plane-orientation function and the space-orientation function of whiskers in whisker-reinforced metal matrix composites was analyzed theoretically. The actual orientation of whiskers in the as- cast 20%SiC_W/Mg composite (SiC_W content in volume fraction) were investigated, and the elastic modulus of the composite was measured with an ultrasonic velocity analyzer. Results show that there is an evident difference be- tween the plane-orientation function and the space-orientation function of whiskers and the space-orientation function can represent the actual condition of the composite. Only by using the space-orientation function of whiskers, the difference of elastic modulus of the as-cast composite in different directions can be explained reasonably.
基金This work has been supported through the Natural Sciences and Engineering Research Council of Canada(NSERC)PGS D3-518886,NSERC Discovery Grants 341275
文摘Elastic modulus(E)interpretation is debatable with limited literature detailing the impact of systemcompliance.To address this impact,a comprehensive testing schedule using an aluminium 6061(Al)sample is carried out on several systems under various test setups.Al is chosen as it is extruded and adheres to well defined shape tolerances and elastic properties.A robust method,using the Savitzky-Golay filter,is introduced to identify significant slope changes in the stressestrain curve.Since the load in the test system is well defined,the recorded deformation is corrected to the expected value of Al resulting in a system-compliance factor.The results across the testing systems and test setups showed significant variance,with the recorded E always lower than the anticipated EAl.The number of components within the system over which the deformation is measured had the most significant impact,lowering the expected E by up to 50%.Additionally,the system-compliance factor is inconsistent across different systems and setups.Thus,it is evidently proved that each setup must be separately evaluated for its system-compliance and that no single value exists across systems and setups.The findings are then projected onto a series of uniaxial compressive strength(UCS)tests carried out on Stanstead granite(SS GR)samples.The corrected Et50 and Eavg values for system-compliance of the samples are within1%for each system as opposed to being50%pre-correction.The findings conclude that it is deemed necessary and of utmost importance that the deformation be corrected to accommodate the systemcompliance to obtain reliable results.
文摘By using the system of image analyzer connected with scanning electron microscope, the whisker orientation in the SiC w/6061Al alloy composite as squeeze cast was measured. According to the shear lag model and the actual distribution function of whisker in composite, the inhomogeneity of elastic modulus in composite was analyzed. With the method of ultrasonic velocity, the elastic modulus of composite was measured. The results showed that, the whiskers of composite are preferred in an orientation normal to the direction of squeeze cast. The higher the volume fraction of whisker, the more extent of preferred orientation of it, and the inhomogeneity of elastic modulus is mainly due to the differences of whisker distribution in composite.
基金Ac plied Fundamental Research Fund of Sichuan Province 1998(19), P.R.China Fund of Material and Structural Failure Mechanic
文摘Based on the experimental and theoretical analysis, the tensile elastic modulus, strength and fracture characteristics of squeeze casting δ-Al2O3/Al alloy composites were studied. The fracture characteristics of composites were observed by SEM. The elastic modulus was predicted by the finite element method based on the energy equivalence principle, and the strength was predicted by the statistical integration average method using the maximum energy criterion of composite strength. In the prediction, the distribution density functions of the fiber’s. orientation and length were considered. These functions were gained by experimental measurement. It is shown that the predicted results are in agreement with the experimental values well and the microstructure feature of composites controls the fracture characteristics.
文摘Toarcian claystone such as that of the Callovo-Oxfordian is a qualified multiphase material. The claystone samples tested in this study are composed of four main mineral phases: silicates(clay minerals, quartz,feldspars, micas)(z86%), sulphides(pyrite)(z3%), carbonates(calcite, dolomite)(z10%) and organic kerogen(z1%). Three sets of measurements of the modulus of deformability were compared as determined in(i) nanoindentation tests with a constant indentation depth of 2 mm,(ii) micro-indentation tests with a constant indentation depth of 20 mm, and(iii) meso-compression tests with a constant displacement of 200 mm. These three experimental methods have already been validated in earlier studies. The main objective of this study is to demonstrate the influence of the scaling effect on the modulus of deformability of the material. Different frequency distributions of the modulus of deformability were obtained at the different sample scales:(i) in nano-indentation tests, the distribution was spread between 15 GPa and 90 GPa and contained one peak at34 GPa and another at 51 GPa;(ii) in the micro-indentation tests, the distribution was spread between 25 GPa and 60 GPa and displayed peaks at 26 GPa and 37 GPa; and(iii) in the meso-compression tests, a narrow frequency distribution was obtained, ranging from 25 GPa to 50 GPa and with a maximum at around 35 GPa.
文摘Rock properties exhibit spatial variabilities due to complex geological processes such as sedimentation,metamorphism, weathering, and tectogenesis. Although recognized as an important factor controlling the safety of geotechnical structures in rock engineering, the spatial variability of rock properties is rarely quantified. Hence, this study characterizes the autocorrelation structures and scales of fluctuation of two important parameters of intact rocks, i.e. uniaxial compressive strength(UCS) and elastic modulus(EM).UCS and EM data for sedimentary and igneous rocks are collected. The autocorrelation structures are selected using a Bayesian model class selection approach and the scales of fluctuation for these two parameters are estimated using a Bayesian updating method. The results show that the autocorrelation structures for UCS and EM could be best described by a single exponential autocorrelation function. The scales of fluctuation for UCS and EM respectively range from 0.3 m to 8.0 m and from 0.3 m to 8.4 m.These results serve as guidelines for selecting proper autocorrelation functions and autocorrelation distances for rock properties in reliability analyses and could also be used as prior information for quantifying the spatial variability of rock properties in a Bayesian framework.
基金Sponsored by the National High Technology Research and Development Program of China(Grant No.2015AA042501)
文摘The mismatch of elasticity modulus has limited the application of titanium alloys in medical implants,and porous structures have been proved effective to deal with this problem. However,the manufacturing of porous structures has been restricted from conventional technologies. In this study,selective laser melting( SLM) technology was employed to produce a set of Ti-6Al-4V porous samples based on cubic lattices with varying size of strut width from 200 μm to 600 μm. Then the compression tests were conducted to analyze the influence of the strut width on the elasticity modulus and the ultimate strength. The result shows both of them increases linearly with the growth of strut width or with the decrease of porosity,and the elasticity modulus of porous parts is largely reduced and actually meets the requirement of clinical application. Additionally,a finite element model was established to verify the un-uniform stress distribution of porous parts. It reveals that fractures always initially occur at the vertical struts along the force direction which suffer from the main deformation.
文摘Internal friction and elastic modulus of ternary Mn-Cu-Al alloys containing 56—60wt-% Mn,0-3.59 wt-% Al were measured with acoustic frequency,1 kHz,in the tempera-ture range of-150 to 150℃.It was found that when the specimen was aged in the temperaturerange under the spinodal curve within the miscibility gap(400—500℃),the internal fric-tion increases with an increase of the aging time and reaches a maximum value at a certain ag-ing time which is shorter with a higher aging temperature.Two internal friction peaks whichdid not appear before the aging were observed above room temperature after a definite agingtime.These are respectively the martensitic tranformation peak and the relaxation peak orig-inating from the stress-induced movement of the twin boundaries.The former peak shifts to-ward higher temperatures with an increase of the aging time,whereas the relaxation peak ap-pearing at 15℃,is independent of the aging time and temperature.The activation energy as-sociated with the relaxation peak was found to be 0.56 eV which is about the same as that ofthe relaxation peak in binary alloy containing 90 wt-% Mn.It was also found that thehardness,strength and the brittleness of the specimen increase when aged below the spinodalcurve within the miscibility gap.The addition or Al enhances the strength but reduces the in-ternal friction of the specimen.A choice of suitable aging time and temperature can give anoptimum compromise of high strength and high internal friction.Analysis of experimental re-sults suggests that spinodal decomposition leads to Mn-rich zones in the specimen and thuscauses the phase transformation and the change of mechanical properties of the specimen.
基金supported by the National Natural Science Foundation of China (No. 50768001)the Foundation of New Century Excellent Talents in University (No. NCET-04-0834)the Guangxi Natural Science Foundation (No. 0728026)
文摘A new strategy for elastic modulus adjustment is proposed based on the element bearing ratio (EBR),and the elastic modulus reduction method (EMRM) is proposed for limit load evaluation of frame structures. The EBR is defined employing the generalized yield criterion,and the reference EBR is determined by introducing the extrema and the degree of uniformity of EBR in the structure. The elastic modulus in the element with an EBR greater than the reference one is reduced based on the linear elastic finite element analysis and the equilibrium of strain energy. The lower-bound of limit-loads of frame structures are analyzed and the numerical example demonstrates the flexibility,accuracy and effciency of the proposed method.
文摘Two semi-empirical approaches for prediction of elastic modulus of biphasic composites have been proposed. Developed relations are for pore free matrix and pore free filler and found to depend on nonlinear contribution of volume fraction of constituents as well as ratio of elastic properties of individual phases. These relations are applied for the calculation of effective elastic modulus mainly for Al2O3-NiAl, SiC-Al, Alumina-Zirconia, Al-Al2O3, W-glass and Flax-Resin composite materials. Theoretical predictions using developed relations are compared with experimental data. It is found that the predicted values of effective elastic modulus using modified relations are quite close to the experimental results.
基金Project supported by the National Natural Science Foundation of China (Grant No.11072104)the Scientific Research Program for Higher Schools of Inner Mongolia (Grant No.NJZY13013)
文摘The size-dependent elastic property of rectangular nanobeams(nanowires or nanoplates) induced by the surface elasticity effect is investigated by using a developed modified core-shell model.The effect of surface elasticity on the elastic modulus of nanobeams can be characterized by two surface related parameters,i.e.,inhomogeneous degree constant and surface layer thickness.The analytical results show that the elastic modulus of the rectangular nanobeam exhibits a distinct size effect when its characteristic size reduces below 100 nm.It is also found that the theoretical results calculated by a modified core-shell model have more obvious advantages than those by other models(core-shell model and core-surface model)by comparing them with relevant experimental measurements and computational results,especially when the dimensions of nanostructures reduce to a few tens of nanometers.
文摘The four point bending method was applied to measure X ray elastic constants(XEC) of (422) and (331) planes of TiN coating. Elastic Modulus and XECs of all the crystal planes were calculated by Kroner method. The results from the calculation and the experiment were compared. It is concluded that the XECs values of same film prepared by different techniques scatter a little because of the effects of stoichiometric proportion and microstructure of films. [
基金Project(2007AA04Z408) supported by the National High-Tech Research and Development Program of ChinaProject(50735006) supported by the National Natural Science Foundation of China
文摘The distribution and magnitude of surface and subsurface stresses of the single-layer sprayed-coatings on monolithic substrates were investigated by finite element method(FEM) .The models of coating configurations with different thicknesses and elastic modulus ratios of coating to substrate were introduced,and the effects of thickness and elastic modulus ratio on the stresses were addressed.The calculation results show that the coating/substrate interface shear stress obviously decreases with increasing coating thickness,due to the location of the maximum shear stress moving away from the coating/substrate interface.At the same time,the magnitude of von Mises stress also declines in the case of thicker coatings.However,the high elastic modulus ratio results in extremely high maximum shear stress and the severe discontinuity of the von Mises stress curves,which leads to the intensive stress concentration on the coating/substrate interface.So the coating configurations with the larger coating thickness and lower difference of elastic modulus between coating and substrate exhibit excellent resistant performance of rolling contact fatigue(RCF).
文摘Based on the Hertzian granular contact mechanics model, the paper built up a Macroscopic Young’s Elastic Modulus of particle/granular packing rock layers, and built up a ties to connecting Young’s Elastic Modulus of sand particle in Meso and the Macroscopic Young’s Modulus of granular packing rock layers. The Macroscopic Young’s Modulus of granular packing rock layers is far less than the Young’s Modulus of sand particle. The Macroscopic Young’s Modulus of granular packing rock layers is proportioned to the powers of 1/3 of the vertical contact force of sand particles. The Macroscopic Young’s Modulus is inversely proportional to particle diameter. The paper calculated the vertical contact force of five types aligning mode of the particles. When equal stress, the increased of the coordination number lead to the decrease of the contact force fn, this lead to the coordination number is an inverse proportion to Macroscopic Young’s Modulus. But the larger coordination number change only means very little Macroscopic Young’s Modulus change.
