Marine thin plates are susceptible to welding deformation owing to their low structural stiffness.Therefore,the efficient and accurate prediction of welding deformation is essential for improving welding quality.The t...Marine thin plates are susceptible to welding deformation owing to their low structural stiffness.Therefore,the efficient and accurate prediction of welding deformation is essential for improving welding quality.The traditional thermal elastic-plastic finite element method(TEP-FEM)can accurately predict welding deformation.However,its efficiency is low because of the complex nonlinear transient computation,making it difficult to meet the needs of rapid engineering evaluation.To address this challenge,this study proposes an efficient prediction method for welding deformation in marine thin plate butt welds.This method is based on the coupled temperature gradient-thermal strain method(TG-TSM)that integrates inherent strain theory with a shell element finite element model.The proposed method first extracts the distribution pattern and characteristic value of welding-induced inherent strain through TEP-FEM analysis.This strain is then converted into the equivalent thermal load applied to the shell element model for rapid computation.The proposed method-particularly,the gradual temperature gradient-thermal strain method(GTG-TSM)-achieved improved computational efficiency and consistent precision.Furthermore,the proposed method required much less computation time than the traditional TEP-FEM.Thus,this study lays the foundation for future prediction of welding deformation in more complex marine thin plates.展开更多
The valence subband energies and wave functions of a tensile strained quantum well are calculated by the plane wave expansion method within the 6×6 Luttinger Kohn model.The effect of the number and period of pla...The valence subband energies and wave functions of a tensile strained quantum well are calculated by the plane wave expansion method within the 6×6 Luttinger Kohn model.The effect of the number and period of plane waves used for expansion on the stability of energy eigenvalues is examined.For practical calculation,it should choose the period large sufficiently to ensure the envelope functions vanish at the boundary and the number of plane waves large enough to ensure the energy eigenvalues keep unchanged within a prescribed range.展开更多
Sensitivity analysis and topology optimization of microstructures using strain energy-based method is presented. Compared with homogenization method, the strain energy-based method has advantages of higher computing e...Sensitivity analysis and topology optimization of microstructures using strain energy-based method is presented. Compared with homogenization method, the strain energy-based method has advantages of higher computing efficiency and simplified programming. Both the dual convex programming method and perimeter constraint scheme are used to optimize the 2D and 3D microstructures. Numerical results indicate that the strain energy-based method has the same effectiveness as that of homogenization method for orthotropic materials.展开更多
A thorough understanding of the texture evolution of near-αtitanium alloys during the hot metal forming can help obtain an optimal crystallographic texture and material performance.The strain state has an obvious eff...A thorough understanding of the texture evolution of near-αtitanium alloys during the hot metal forming can help obtain an optimal crystallographic texture and material performance.The strain state has an obvious effect on the texture evolution of near-αtitanium alloys during the hot metal forming.In this paper,the texture evolution of a near-αTA15 titanium alloy during the hot metal forming under different strain states were discussed based on the crystal plasticity finite element method.It is found that the basal and prismatic slip systems are regarded as the dominant slip modes due to the similar low critical resolved shear stress during the hot metal forming of the TA15 sheet rotating the lattice around the[1010]and 0001 axis,respectively.Once both of them cannot be activated,the pyramidal-2 slipping occurs rotating the lattice around the[1010]axis.The relationship between the texture evolution and strain state is established.All the(0001)orientations form a band perpendicular to the direction of the first principal strain.The width of the band along the direction of the second principal strain depends on the ratio of the compressive effect to the tensile effect of the second principal strain.This relationship can help control the crystallographic texture and mechanical properties of the titanium alloys component during the hot metal forming.展开更多
In recent years, the method of magnetic survey as one of the new techniques in geological and geophysical studies is known. In this study to determine the shape of the stress field of the two methods, Anisotropy of Ma...In recent years, the method of magnetic survey as one of the new techniques in geological and geophysical studies is known. In this study to determine the shape of the stress field of the two methods, Anisotropy of Magnetic Susceptibility (AMS) and paleostress?have been used. Paleomagnetism is the characteristics of magnetic rocks. Some issues in associated with the past places of continental and oceanic plates can be solved. AMS is one of the paleomagnetism methods that pay to measurement of parameters (which are reflector of the magnetic fabrics rocks). It is presenting an ellipsoid with three-axis perpendicular to each other that defines magnetic ellipsoid. In this regard, the number of 12 stations in different rocks (Jurassic to Quaternary) in the southern region of Ardebil sampling was conducted. In this connection, the study of magnetic fabrics has shown an elliptical magnetic susceptibility with the prolate shape. For the separation of paleostress phases in the Khalkhal area using the analysis of the paleostress based on the study of heterogeneous fault-slip data and sliding lineaments. Firstly, data were picked from 10 stations, and after their analysis, the elliptical shape (prolate) has been determinated. The shape of the ellipsoid, based on AMS and paleostress methods and their results show that in both methods the shape of the stress field is prolate.展开更多
Structural strain modes are able to detect changes in local structural performance, but errors are inevitably intermixed in the measured data. In this paper, strain modal parameters are considered as random variables,...Structural strain modes are able to detect changes in local structural performance, but errors are inevitably intermixed in the measured data. In this paper, strain modal parameters are considered as random variables, and their uncertainty is analyzed by a Bayesian method based on the structural frequency response function （FRF）. The estimates of strain modal parameters with maximal posterior probability are determined. Several independent measurements of the FRF of a four-story reinforced concrete flame structural model were performed in the laboratory. The ability to identify the stiffness change in a concrete column using the strain mode was verified. It is shown that the uncertainty of the natural frequency is very small. Compared with the displacement mode shape, the variations of strain mode shapes at each point are quite different. The damping ratios are more affected by the types of test systems. Except for the case where a high order strain mode does not identify local damage, the first order strain mode can provide an exact indication of the damage location.展开更多
Optical full-field measurement methods are now widely applied in various domains. In general,the displacement fields can be directly obtained from the measurement,however in mechanical analysis strain fields are prefe...Optical full-field measurement methods are now widely applied in various domains. In general,the displacement fields can be directly obtained from the measurement,however in mechanical analysis strain fields are preferred.To extract strain fields from noisy displacement fields is always a challenging topic.In this study,a finite element method for smoothing displacement fields and calculating strain fields is proposed.An experimental test case on a holed aluminum specimen under tension is applied to validate this method.The heterogeneous displacement fields are measured by digital image correlation(DIC).By this proposed method,the result shows that the measuring noise on experimental displacement fields can be successfully removed,and strain fields can be reconstructed in the arbitrary area.展开更多
Due to the current trend towards lightweight design in automotive industry,hollow stepped gear shafts for automobile and its radial forging process are widely investigated.Utilizing coupled finite element thermo-mecha...Due to the current trend towards lightweight design in automotive industry,hollow stepped gear shafts for automobile and its radial forging process are widely investigated.Utilizing coupled finite element thermo-mechanical model,radial forging process of a hollow stepped gear shaft for automobile was simulated.The optimal combination of three process parameters including initial temperature,rotation rate and radial reduction was also selected using orthogonal design method.To examine the strain inhomogeneity of the forging workpiece,the strain inhomogeneity factor was introduced.The results reveal that the maximum effective strain and the minimum effective strain appeared in the outermost and innermost zones of different cross sections for the hollow stepped gear shaft,respectively.Optimal forging parameters are determined as a combination of initial temperature of 780°C,rotation rate of 21°/stroke and radial reduction of 3 mm.展开更多
The fatigue lives of materials and structures at different strain levels show het- eroscedasticity. In addition when the number of test specimens is insufficient, the fatigue strength coefficient and fatigue ductility...The fatigue lives of materials and structures at different strain levels show het- eroscedasticity. In addition when the number of test specimens is insufficient, the fatigue strength coefficient and fatigue ductility coefficient of the fitting parameters in the total strain life equa- tion may not have definite physical significance. In this work, a maximum likelihood method for estimating probabilistic strain amplitude fatigue life curves is presented based on the fatigue lives at different strain levels. The proposed method is based on the general basic assumption that the logarithm of fatigue life at an arbitrary strain level is normally distributed. The rela- tionship among the parameters of total strain life equation, monotonic ultimate tensile stress and percentage reduction of area is adopted. The presented approach is finally illustrated by two applications. It is shown that probabilistic strain amplitude-fatigue life curves can be eas- ily estimated based on the maximum likelihood method. The results show that fatigue lives at different strain levels have heteroscedasticity and the values of fatigue strength coefficient and fatigue ductility coefficient obtained by the proposed method are close to those of the true tensile fracture stress and true tensile fracture strain.展开更多
The isotropic and anisotropic behaviors are considered as the important formats of the constitutive behaviors,and can also be called the global properties.To improve the identification ability of virtual fields method...The isotropic and anisotropic behaviors are considered as the important formats of the constitutive behaviors,and can also be called the global properties.To improve the identification ability of virtual fields method(VFM)when the global properties are unknown,this paper proposes the strain correlation method(SCM)to determine the global properties before the parameter identification using the VFM.Firstly,the basic principle of SCM is described in detail.Then,the feasibility and accuracy of SCM are verified through the numerical experiments based on the three-point bending configuration and the real experiment of polymethyl methacrylate(PMMA).The influence of the additive Gaussian white noise,local errors in the strain fields,and missing data at the specimen edges on the characterization results are evaluated.The results show that the SCM has good noise immunity and lower accuracy requirements for the strain fields.As an application,the mechanical properties of Ti-6A1-4V alloys fabricated by selective laser melting(SLM)are characterized by the SCM.The results show that the alloys are isotropic,and the isotropic VFM is utilized to determine the mechanical parameters.By using the SCM,the accuracy of identification results can be improved for the isotropic or bidirectional reinforced orthotropic materials when using VFM.展开更多
C^1 natural element method （C^1 NEM） is applied to strain gradient linear elasticity, and size effects on mi crostructures are analyzed. The shape functions in C^1 NEM are built upon the natural neighbor interpolati...C^1 natural element method （C^1 NEM） is applied to strain gradient linear elasticity, and size effects on mi crostructures are analyzed. The shape functions in C^1 NEM are built upon the natural neighbor interpolation （NNI）, with interpolation realized to nodal function and nodal gradient values, so that the essential boundary conditions （EBCs） can be imposed directly in a Galerkin scheme for partial differential equations （PDEs）. In the present paper, C^1 NEM for strain gradient linear elasticity is constructed, and sev- eral typical examples which have analytical solutions are presented to illustrate the effectiveness of the constructed method. In its application to microstructures, the size effects of bending stiffness and stress concentration factor （SCF） are studied for microspeciem and microgripper, respectively. It is observed that the size effects become rather strong when the width of spring for microgripper, the radius of circular perforation and the long axis of elliptical perforation for microspeciem come close to the material characteristic length scales. For the U-shaped notch, the size effects decline obviously with increasing notch radius, and decline mildly with increasing length of notch.展开更多
In order to establish the quantitative relationship between equivalent strain and the performance index of the deformed material within the range of certain passes for equal channel angular processing （ECAP）, a new ...In order to establish the quantitative relationship between equivalent strain and the performance index of the deformed material within the range of certain passes for equal channel angular processing （ECAP）, a new approach to characterize the equivalent strain was proposed. The results show that there exists better accordance between mechanical property （such as hardness or strength） and equivalent strain after rolling and ECAP in a certain range of deformation amount, and Gauss equation can be satisfied among the equivalent strain and the mechanical properties for ECAP. Through regression analysis on the data of hardness and strength after the deformation, a more generalized expression of equivalent strain for ECAP is proposed as：ε=k0exp[-（k1M-k2）^2], where M is the strength or hardness of the material, k1 is the modified coefficient （k1∈ （0, 1））, ko and k2 are two parameters dependent on the critical strain and mechanical property that reaches saturation state for the material, respectively. In this expression the equivalent strain for ECAP is characterized novelly through the mechanical parameter relating to material property rather than the classical geometry equation.展开更多
New strain induced melt activated (new SIMA) method for preparing AZ91D magnesium alloy semi-solid billet is introduced by applying equal channel angular extrusion into strain induced step in SIMA method, by which sem...New strain induced melt activated (new SIMA) method for preparing AZ91D magnesium alloy semi-solid billet is introduced by applying equal channel angular extrusion into strain induced step in SIMA method, by which semi-solid billet with fine spheroidal grains and average grain size of 18 μm can be prepared. Furthermore, average grain size of semi-solid billet is reduced with increasing extrusion pass of AZ91D magnesium alloy obtained in ECAE process. By using semi-solid billet prepared by new SIMA, thixoforged magazine plates component with high mechanical properties such as yield strength of 201.4 MPa, ultimate tensile strength of 321.8 MPa and elongation of 15.3%, can be obtained.展开更多
In this paper a new method for preventing welding hot cracking—the inverse strain method(ISM)is developed on the principle of welding mechan- ics.Effectiveness and feasiblity of method in preventing welding hot crack...In this paper a new method for preventing welding hot cracking—the inverse strain method(ISM)is developed on the principle of welding mechan- ics.Effectiveness and feasiblity of method in preventing welding hot cracking of high strength aluminum alloy LY12CZ by synchronous rolling during welding (SRDW)along both sides of the weld at a suitable distance behind the welding arc are examined.Experimental resulte indicate that welding hot cracking of LY12CY can be effectively prevented and the mechanical properties of welded joint can also be improved by the method.It is an important new solution for preventing hot cracking in welding of sheet metal.展开更多
This paper presents a finite element framework for imposing frictional contact conditions on embedded fracture faces,implemented by the constant-strain assumed enhanced strain(AES)method,where penalty method is used t...This paper presents a finite element framework for imposing frictional contact conditions on embedded fracture faces,implemented by the constant-strain assumed enhanced strain(AES)method,where penalty method is used to impose both non-penetration constraint and Coulomb’s law of friction.The proposed constant-strain AES method for modeling embedded frictional contact can be cast into an integration algorithm similar to those used in the classical plasticity theory,where displacement jump is calculated from the local traction equilibrium at Gauss point,so the method does not introduce any additional global degrees of freedom.Moreover,constant-strain elements are often desirable in practice because they can be easily created automatically for large-scale engineering applications with complicated geometries.As encountered in other enriched finite element methods for frictional contact,the problem of normal contact pressure oscillations is also observed in the constant-strain AES method.Therefore,we developed a strain-smoothing procedure to effectively mitigate the oscillations.We investigated and verified the proposed AES framework through several numerical examples,and illustrated the capability of this method in solving challenging nonlinear frictional contact problems.展开更多
This paper investigates process parameter effects on microstructure and mechanical properties of the tubes processed via recently developed friction assisted tube straining(FATS)method.For this purpose,design of exper...This paper investigates process parameter effects on microstructure and mechanical properties of the tubes processed via recently developed friction assisted tube straining(FATS)method.For this purpose,design of experiment was used to arrange finite element analyses and experimental tests.Numerical and experimental tests were executed by changing rotary speed,feed rate and die angle.Taguchi design results show that increasing feed rate and decreasing rotary speed enhance Zener-Hollomon(Z)parameter and decrease average grain size,while die angle has no considerable effect.Increasing Z value reduces grain size and enhances flow stress of the processed samples,while the experiment with the highest Z value refines initial microstructure from 40 to 8μm and increases flow stress by 5 times.展开更多
In this paper,we mainly study the time-space fractional strain wave equation in microstructured solids.He’s variational method,combined with the two-scale transform are implemented to seek the solitary and periodic w...In this paper,we mainly study the time-space fractional strain wave equation in microstructured solids.He’s variational method,combined with the two-scale transform are implemented to seek the solitary and periodic wave solutions of the time-space strain wave equation.The main advantage of the variational method is that it can reduce the order of the differential equation,thus simplifying the equation,making the solving process more intuitive and avoiding the tedious solving process.Finally,the numerical results are shown in the form of 3D and 2D graphs to prove the applicability and effectiveness of the method.The obtained results in this work are expected to shed a bright light on the study of fractional nonlinear partial differential equations in physics.展开更多
In this paper, the stress-strain curve of material is fitted by polygonal line composed of three lines. According to the theory of proportional loading in elastoplasticity, we simplify the complete stress-strain relat...In this paper, the stress-strain curve of material is fitted by polygonal line composed of three lines. According to the theory of proportional loading in elastoplasticity, we simplify the complete stress-strain relations, which are given by the increment theory of elastoplasticity. Thus, the finite element equation with the solution of displacement is derived. The assemblage elastoplastic stiffness matrix can be obtained by adding something to the elastic matrix, hence it will shorten the computing time. The determination of every loading increment follows the von Mises yield criteria. The iterative method is used in computation. It omits the redecomposition of the assemblage stiffness matrix and it will step further to shorten the computing time. Illustrations are given to the high-order element application departure from proportional loading, the computation of unloading fitting to the curve and the problem of load estimation.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No.51975138the High-Tech Ship Scientific Research Project from the Ministry of Industry and Information Technology under Grant No.CJ05N20the National Defense Basic Research Project under Grant No.JCKY2023604C006.
文摘Marine thin plates are susceptible to welding deformation owing to their low structural stiffness.Therefore,the efficient and accurate prediction of welding deformation is essential for improving welding quality.The traditional thermal elastic-plastic finite element method(TEP-FEM)can accurately predict welding deformation.However,its efficiency is low because of the complex nonlinear transient computation,making it difficult to meet the needs of rapid engineering evaluation.To address this challenge,this study proposes an efficient prediction method for welding deformation in marine thin plate butt welds.This method is based on the coupled temperature gradient-thermal strain method(TG-TSM)that integrates inherent strain theory with a shell element finite element model.The proposed method first extracts the distribution pattern and characteristic value of welding-induced inherent strain through TEP-FEM analysis.This strain is then converted into the equivalent thermal load applied to the shell element model for rapid computation.The proposed method-particularly,the gradual temperature gradient-thermal strain method(GTG-TSM)-achieved improved computational efficiency and consistent precision.Furthermore,the proposed method required much less computation time than the traditional TEP-FEM.Thus,this study lays the foundation for future prediction of welding deformation in more complex marine thin plates.
文摘The valence subband energies and wave functions of a tensile strained quantum well are calculated by the plane wave expansion method within the 6×6 Luttinger Kohn model.The effect of the number and period of plane waves used for expansion on the stability of energy eigenvalues is examined.For practical calculation,it should choose the period large sufficiently to ensure the envelope functions vanish at the boundary and the number of plane waves large enough to ensure the energy eigenvalues keep unchanged within a prescribed range.
基金National Natural Science Foundation of China （90405016, 10676028） 973 Program （2006CB601205）+1 种基金 863 Project （2006AA04Z 122） Aeronautical Science Foundation （04B53080, 2006ZA 53006） and 111 Project （B07050）
文摘Sensitivity analysis and topology optimization of microstructures using strain energy-based method is presented. Compared with homogenization method, the strain energy-based method has advantages of higher computing efficiency and simplified programming. Both the dual convex programming method and perimeter constraint scheme are used to optimize the 2D and 3D microstructures. Numerical results indicate that the strain energy-based method has the same effectiveness as that of homogenization method for orthotropic materials.
基金financially supported by the National Natural Science Foundation of China(No.51401065).
文摘A thorough understanding of the texture evolution of near-αtitanium alloys during the hot metal forming can help obtain an optimal crystallographic texture and material performance.The strain state has an obvious effect on the texture evolution of near-αtitanium alloys during the hot metal forming.In this paper,the texture evolution of a near-αTA15 titanium alloy during the hot metal forming under different strain states were discussed based on the crystal plasticity finite element method.It is found that the basal and prismatic slip systems are regarded as the dominant slip modes due to the similar low critical resolved shear stress during the hot metal forming of the TA15 sheet rotating the lattice around the[1010]and 0001 axis,respectively.Once both of them cannot be activated,the pyramidal-2 slipping occurs rotating the lattice around the[1010]axis.The relationship between the texture evolution and strain state is established.All the(0001)orientations form a band perpendicular to the direction of the first principal strain.The width of the band along the direction of the second principal strain depends on the ratio of the compressive effect to the tensile effect of the second principal strain.This relationship can help control the crystallographic texture and mechanical properties of the titanium alloys component during the hot metal forming.
文摘In recent years, the method of magnetic survey as one of the new techniques in geological and geophysical studies is known. In this study to determine the shape of the stress field of the two methods, Anisotropy of Magnetic Susceptibility (AMS) and paleostress?have been used. Paleomagnetism is the characteristics of magnetic rocks. Some issues in associated with the past places of continental and oceanic plates can be solved. AMS is one of the paleomagnetism methods that pay to measurement of parameters (which are reflector of the magnetic fabrics rocks). It is presenting an ellipsoid with three-axis perpendicular to each other that defines magnetic ellipsoid. In this regard, the number of 12 stations in different rocks (Jurassic to Quaternary) in the southern region of Ardebil sampling was conducted. In this connection, the study of magnetic fabrics has shown an elliptical magnetic susceptibility with the prolate shape. For the separation of paleostress phases in the Khalkhal area using the analysis of the paleostress based on the study of heterogeneous fault-slip data and sliding lineaments. Firstly, data were picked from 10 stations, and after their analysis, the elliptical shape (prolate) has been determinated. The shape of the ellipsoid, based on AMS and paleostress methods and their results show that in both methods the shape of the stress field is prolate.
基金Ministry of Construction of China through the Science and Technique Program Grant No.06-k6-13Guangzhou Construction Technological Development Foundation through Grant No.200409+1 种基金Guangdong Province Natural Science Foundation through Grant No.5300381 Guangzhou Science and Technique Bureau through Science and Technique Program Grant No.2006J1-C0451
文摘Structural strain modes are able to detect changes in local structural performance, but errors are inevitably intermixed in the measured data. In this paper, strain modal parameters are considered as random variables, and their uncertainty is analyzed by a Bayesian method based on the structural frequency response function （FRF）. The estimates of strain modal parameters with maximal posterior probability are determined. Several independent measurements of the FRF of a four-story reinforced concrete flame structural model were performed in the laboratory. The ability to identify the stiffness change in a concrete column using the strain mode was verified. It is shown that the uncertainty of the natural frequency is very small. Compared with the displacement mode shape, the variations of strain mode shapes at each point are quite different. The damping ratios are more affected by the types of test systems. Except for the case where a high order strain mode does not identify local damage, the first order strain mode can provide an exact indication of the damage location.
基金supported by the National Basic Research Program of China("973"Project, Grant No.2010CB631005,2011CB606105)the National Natural Science Foundation of China(Grant No.10625209, 10732080,90916010)+2 种基金China Postdoctoral Science Foundation (Grant No.20090460335)Specialized Research Fund for the Doctoral Program of Higher Education(Grant No.20090002110048)the opening funds from the State Key Laboratory of Explosion Science and Technology (KFJJ10-18Y)
文摘Optical full-field measurement methods are now widely applied in various domains. In general,the displacement fields can be directly obtained from the measurement,however in mechanical analysis strain fields are preferred.To extract strain fields from noisy displacement fields is always a challenging topic.In this study,a finite element method for smoothing displacement fields and calculating strain fields is proposed.An experimental test case on a holed aluminum specimen under tension is applied to validate this method.The heterogeneous displacement fields are measured by digital image correlation(DIC).By this proposed method,the result shows that the measuring noise on experimental displacement fields can be successfully removed,and strain fields can be reconstructed in the arbitrary area.
基金Projects(51774054,51974050)supported by the National Natural Science Foundation of China。
文摘Due to the current trend towards lightweight design in automotive industry,hollow stepped gear shafts for automobile and its radial forging process are widely investigated.Utilizing coupled finite element thermo-mechanical model,radial forging process of a hollow stepped gear shaft for automobile was simulated.The optimal combination of three process parameters including initial temperature,rotation rate and radial reduction was also selected using orthogonal design method.To examine the strain inhomogeneity of the forging workpiece,the strain inhomogeneity factor was introduced.The results reveal that the maximum effective strain and the minimum effective strain appeared in the outermost and innermost zones of different cross sections for the hollow stepped gear shaft,respectively.Optimal forging parameters are determined as a combination of initial temperature of 780°C,rotation rate of 21°/stroke and radial reduction of 3 mm.
基金supported by the National Natural Science Foundation of China(No.51475022)
文摘The fatigue lives of materials and structures at different strain levels show het- eroscedasticity. In addition when the number of test specimens is insufficient, the fatigue strength coefficient and fatigue ductility coefficient of the fitting parameters in the total strain life equa- tion may not have definite physical significance. In this work, a maximum likelihood method for estimating probabilistic strain amplitude fatigue life curves is presented based on the fatigue lives at different strain levels. The proposed method is based on the general basic assumption that the logarithm of fatigue life at an arbitrary strain level is normally distributed. The rela- tionship among the parameters of total strain life equation, monotonic ultimate tensile stress and percentage reduction of area is adopted. The presented approach is finally illustrated by two applications. It is shown that probabilistic strain amplitude-fatigue life curves can be eas- ily estimated based on the maximum likelihood method. The results show that fatigue lives at different strain levels have heteroscedasticity and the values of fatigue strength coefficient and fatigue ductility coefficient obtained by the proposed method are close to those of the true tensile fracture stress and true tensile fracture strain.
基金This research was financially supported by the National Key Research and Development Program of China(Grant 2017YFB1103900)the National Science and Technology Major Project(Grant 2017-VI-0003-0073)+1 种基金the National Natural Science Foundation of China(Grant 11672153)Hubei Provincial Major Program of Technological Innovation(Grant 2017AAA121).
文摘The isotropic and anisotropic behaviors are considered as the important formats of the constitutive behaviors,and can also be called the global properties.To improve the identification ability of virtual fields method(VFM)when the global properties are unknown,this paper proposes the strain correlation method(SCM)to determine the global properties before the parameter identification using the VFM.Firstly,the basic principle of SCM is described in detail.Then,the feasibility and accuracy of SCM are verified through the numerical experiments based on the three-point bending configuration and the real experiment of polymethyl methacrylate(PMMA).The influence of the additive Gaussian white noise,local errors in the strain fields,and missing data at the specimen edges on the characterization results are evaluated.The results show that the SCM has good noise immunity and lower accuracy requirements for the strain fields.As an application,the mechanical properties of Ti-6A1-4V alloys fabricated by selective laser melting(SLM)are characterized by the SCM.The results show that the alloys are isotropic,and the isotropic VFM is utilized to determine the mechanical parameters.By using the SCM,the accuracy of identification results can be improved for the isotropic or bidirectional reinforced orthotropic materials when using VFM.
基金supported by the SDUST Spring Bud (2009AZZ021)Taian Science and Technology Development (20112001)
文摘C^1 natural element method （C^1 NEM） is applied to strain gradient linear elasticity, and size effects on mi crostructures are analyzed. The shape functions in C^1 NEM are built upon the natural neighbor interpolation （NNI）, with interpolation realized to nodal function and nodal gradient values, so that the essential boundary conditions （EBCs） can be imposed directly in a Galerkin scheme for partial differential equations （PDEs）. In the present paper, C^1 NEM for strain gradient linear elasticity is constructed, and sev- eral typical examples which have analytical solutions are presented to illustrate the effectiveness of the constructed method. In its application to microstructures, the size effects of bending stiffness and stress concentration factor （SCF） are studied for microspeciem and microgripper, respectively. It is observed that the size effects become rather strong when the width of spring for microgripper, the radius of circular perforation and the long axis of elliptical perforation for microspeciem come close to the material characteristic length scales. For the U-shaped notch, the size effects decline obviously with increasing notch radius, and decline mildly with increasing length of notch.
基金Projects(50471102,50671089) supported by the National Natural Science Foundation of China
文摘In order to establish the quantitative relationship between equivalent strain and the performance index of the deformed material within the range of certain passes for equal channel angular processing （ECAP）, a new approach to characterize the equivalent strain was proposed. The results show that there exists better accordance between mechanical property （such as hardness or strength） and equivalent strain after rolling and ECAP in a certain range of deformation amount, and Gauss equation can be satisfied among the equivalent strain and the mechanical properties for ECAP. Through regression analysis on the data of hardness and strength after the deformation, a more generalized expression of equivalent strain for ECAP is proposed as：ε=k0exp[-（k1M-k2）^2], where M is the strength or hardness of the material, k1 is the modified coefficient （k1∈ （0, 1））, ko and k2 are two parameters dependent on the critical strain and mechanical property that reaches saturation state for the material, respectively. In this expression the equivalent strain for ECAP is characterized novelly through the mechanical parameter relating to material property rather than the classical geometry equation.
基金Project(50475029, 50605015) supported by the National Natural Science Foundation of China
文摘New strain induced melt activated (new SIMA) method for preparing AZ91D magnesium alloy semi-solid billet is introduced by applying equal channel angular extrusion into strain induced step in SIMA method, by which semi-solid billet with fine spheroidal grains and average grain size of 18 μm can be prepared. Furthermore, average grain size of semi-solid billet is reduced with increasing extrusion pass of AZ91D magnesium alloy obtained in ECAE process. By using semi-solid billet prepared by new SIMA, thixoforged magazine plates component with high mechanical properties such as yield strength of 201.4 MPa, ultimate tensile strength of 321.8 MPa and elongation of 15.3%, can be obtained.
文摘In this paper a new method for preventing welding hot cracking—the inverse strain method(ISM)is developed on the principle of welding mechan- ics.Effectiveness and feasiblity of method in preventing welding hot cracking of high strength aluminum alloy LY12CZ by synchronous rolling during welding (SRDW)along both sides of the weld at a suitable distance behind the welding arc are examined.Experimental resulte indicate that welding hot cracking of LY12CY can be effectively prevented and the mechanical properties of welded joint can also be improved by the method.It is an important new solution for preventing hot cracking in welding of sheet metal.
基金supported by the Fundamental Research Funds for the Central Universities (Grant No.2021FZZX001-14)and ZJU-ZCCC Institute of Collaborative Innovation (Grant No.ZDJG2021005).
文摘This paper presents a finite element framework for imposing frictional contact conditions on embedded fracture faces,implemented by the constant-strain assumed enhanced strain(AES)method,where penalty method is used to impose both non-penetration constraint and Coulomb’s law of friction.The proposed constant-strain AES method for modeling embedded frictional contact can be cast into an integration algorithm similar to those used in the classical plasticity theory,where displacement jump is calculated from the local traction equilibrium at Gauss point,so the method does not introduce any additional global degrees of freedom.Moreover,constant-strain elements are often desirable in practice because they can be easily created automatically for large-scale engineering applications with complicated geometries.As encountered in other enriched finite element methods for frictional contact,the problem of normal contact pressure oscillations is also observed in the constant-strain AES method.Therefore,we developed a strain-smoothing procedure to effectively mitigate the oscillations.We investigated and verified the proposed AES framework through several numerical examples,and illustrated the capability of this method in solving challenging nonlinear frictional contact problems.
文摘This paper investigates process parameter effects on microstructure and mechanical properties of the tubes processed via recently developed friction assisted tube straining(FATS)method.For this purpose,design of experiment was used to arrange finite element analyses and experimental tests.Numerical and experimental tests were executed by changing rotary speed,feed rate and die angle.Taguchi design results show that increasing feed rate and decreasing rotary speed enhance Zener-Hollomon(Z)parameter and decrease average grain size,while die angle has no considerable effect.Increasing Z value reduces grain size and enhances flow stress of the processed samples,while the experiment with the highest Z value refines initial microstructure from 40 to 8μm and increases flow stress by 5 times.
基金supported by Program of Henan Polytechnic University(No.B2018-40)Innovative Scientists and Technicians Team of Henan Provincial High Education(21IRTSTHN016)the Fundamental Research Funds for the Universities of Henan Province。
文摘In this paper,we mainly study the time-space fractional strain wave equation in microstructured solids.He’s variational method,combined with the two-scale transform are implemented to seek the solitary and periodic wave solutions of the time-space strain wave equation.The main advantage of the variational method is that it can reduce the order of the differential equation,thus simplifying the equation,making the solving process more intuitive and avoiding the tedious solving process.Finally,the numerical results are shown in the form of 3D and 2D graphs to prove the applicability and effectiveness of the method.The obtained results in this work are expected to shed a bright light on the study of fractional nonlinear partial differential equations in physics.
文摘In this paper, the stress-strain curve of material is fitted by polygonal line composed of three lines. According to the theory of proportional loading in elastoplasticity, we simplify the complete stress-strain relations, which are given by the increment theory of elastoplasticity. Thus, the finite element equation with the solution of displacement is derived. The assemblage elastoplastic stiffness matrix can be obtained by adding something to the elastic matrix, hence it will shorten the computing time. The determination of every loading increment follows the von Mises yield criteria. The iterative method is used in computation. It omits the redecomposition of the assemblage stiffness matrix and it will step further to shorten the computing time. Illustrations are given to the high-order element application departure from proportional loading, the computation of unloading fitting to the curve and the problem of load estimation.
