The randomness of strength and deformation of concrete material is serious and should be considered both in theoretical analyses such as Finite Element Methods and engineering practice, specially for those structural ...The randomness of strength and deformation of concrete material is serious and should be considered both in theoretical analyses such as Finite Element Methods and engineering practice, specially for those structural members with a uniform stress field, where stresses or strains are approximately the same under loading. A mathematical ap- proach of producing a series of random variables of the ultimate tensile strain in concrete is proposed to describe the randomness ofconcrete deformation. With reinforced concrete finite elements a real model calculation method is found for the randomness of initial cracks determined by a minimum tension strain within the uniform stress fields of concrete members. The proposed methods in our paper have as aim to improve the existing method used by FEM and other rela- tive approaches, which normally pay less attention to randomness with consequences that may possibly differ from testing or practice. The method and sample computation as indicated is meaningful and comply with testing and engi- neering practice.展开更多
The identification of multiple interacting inclusions with uniform internal stresses in an infinite elastic matrix subjected to a uniform remote loading is of fundamental importance in the mechanics and design of part...The identification of multiple interacting inclusions with uniform internal stresses in an infinite elastic matrix subjected to a uniform remote loading is of fundamental importance in the mechanics and design of particulate composite materials.In anti-plane shear and plane deformations,certain sufficient conditions have been established in the literature which guarantee uniform internal stresses inside multiple interacting inclusions displaying various symmetries when the matrix is subjected to specific uniform remote loading.Correspondingly,sufficient conditions which allow for the design of multiple interacting inclusions independent of any specific form of(uniform)remote loading have also been established.In this paper,we demonstrate rigorously that,in all cases,these sufficient conditions are also necessary conditions and indeed allow for the identification of all possible collections of such inclusions.展开更多
The damage variables of describing the material damage state should be chosen first when the research of concrete structures by use of theory of damage theory. The method of calculation of damage parameter by the meas...The damage variables of describing the material damage state should be chosen first when the research of concrete structures by use of theory of damage theory. The method of calculation of damage parameter by the measure of the change of the elastic modulus of concrete specimens is effectively. In this paper, the wedge splitting tests with double bearing of three groups of different initial crack lengths of concrete specimens were conducted, and the stress and the strain of the points with different distance from the initial crack tip measured and calculated, and the damage value with peak stress of the various points were calculated based on the stress-strain curves. From the results of the test, the damage parameter can be confirmed under the non-uniform stress field, and the initial crack length has some influence on the damage parameter, and the longer the initial crack length and the greater the damage parameter.展开更多
This paper provides a review of recent research advances and trends in the area of stability of unstiffened circular cylindrical shells subjected to general non-uniform axial compressive stresses.Only the more importa...This paper provides a review of recent research advances and trends in the area of stability of unstiffened circular cylindrical shells subjected to general non-uniform axial compressive stresses.Only the more important and interesting aspects of the research,judged from a personal viewpoint,are discussed.They can be crudely classified into four categories:(1) shells subjected to non-uniform loads;(2) shells on discrete supports;(3) shells with intended cutouts/holes;and (4) shells with non-uniform settlements.展开更多
Based on the characteristics of 1D waves,the stress uniformity process in specimens under different loading conditions of rectangular and half-sine input waves was analyzed in split Hopkinson pressure bar (SHPB) test....Based on the characteristics of 1D waves,the stress uniformity process in specimens under different loading conditions of rectangular and half-sine input waves was analyzed in split Hopkinson pressure bar (SHPB) test.The results show that the times of an elastic wave propa-gating from one end to the other in a specimen to attain stress equilibrium,is related to input wave-forms and relative mechanical impedance between the specimen and the input/output bars.Here-into,with the increae of the relative impedance,the times decreases under rectangular input waves loading,while it increases under half-sine input wave loading.The dimensionless stress value of specimen corresponding to the status of stress equilibrium increases with the increase of the rela-tive mechanical impedance.However,the dimensionless stress value under half-sine input wave loading is significantly lower than the value under rectangular input wave loading for specimen with low mechanical impedance,and the relative differentia of the dimensionless stress values under two loading conditions decreases with the increase of the relative mechanical impedance.In gen-eral,the forced state of specimen with relatively low mechanical impedance under half-sine input wave loading is evidently superior to the state under rectangular input wave loading in SHPB test,and the advantages of forced state under half-sine input wave loading turns weak with the increase of the relative mechanical impedance.展开更多
In view of the anisotropy,heterogeneity and stress-sensitive permeability in low permeability reservoirs,an analytical well test model was established by introducing the concept of permeability modulus.This model cons...In view of the anisotropy,heterogeneity and stress-sensitive permeability in low permeability reservoirs,an analytical well test model was established by introducing the concept of permeability modulus.This model considered the permeability stress-sensitivity,wellbore storage effect,and the skin effect.The perturbation technique and Laplace transformation were used to solve the mathematical model analytically in Laplace space,and the bottom-hole pressure type curves were plotted and analyzed in real space by using the Stehfest numerical inversion.展开更多
An essential problem in the design of mechanical impact systems is the impact of a piston on a rod. The impact of a semi finite cylindrical piston on a non uniform rod was studied. Based on wave mechanics and characte...An essential problem in the design of mechanical impact systems is the impact of a piston on a rod. The impact of a semi finite cylindrical piston on a non uniform rod was studied. Based on wave mechanics and characteristic line theory, an inverse numerical approach to determine the piston profile was proposed, by means of which the geometry of an impact piston may be determined from the given stress waveform for a given rod profile. Numerical results show that the given stress waveform may be produced by means of the alternatives of design of piston and rod. There is good agreement between the experimental results and numerical results. [展开更多
Current methodologies used for the inference of thin film stress through curvature measurements are strictly restricted to stress and curvature states which are assumed to remain uniform over the entire film/substrate...Current methodologies used for the inference of thin film stress through curvature measurements are strictly restricted to stress and curvature states which are assumed to remain uniform over the entire film/substrate system. By considering a circular thin film/substrate system subject to non-uniform, but axisymmetric misfit strain distributions in the thin film, we derived relations between the film stresses and the misfit strain, and between the plate system＇s curvatures and the misfit strain. These relations feature a “local” part which involves a direct dependence of the stress or curvature components on the misfit strain at the same point, and a “non-local” part which reflects the effect of misfit strain of other points on the location of scrutiny. Most notably, we also derived relations between the polar components of the film stress and those of system curvatures which allow for the experimental inference of such stresses from full-field curvature measurements in the presence of arbitrary radial non-uniformities. These relations also feature a “non-local” dependence on curvatures making a full-field measurement a necessity. Finally, it is shown that the interfacial shear tractions between the film and the substrate are proportional to the radial gradients of the first curvature invariant and can also be inferred experimentally.展开更多
According to the Mohr-Coulomb yield criterion, the stress field of the infinite slope is derived under a vertical uniform load q on the top of the slope. It is indicated that elastic and elasto-plastic states would oc...According to the Mohr-Coulomb yield criterion, the stress field of the infinite slope is derived under a vertical uniform load q on the top of the slope. It is indicated that elastic and elasto-plastic states would occur in the slope. When q is smaller than the critical load, q(p), the slope is in the elastic state. If q equals q(p), the slope is in the critical state, and the plastic deformation would occur along the critical angle. With the increase of q, the plastic zone would extend, and the slope is in the elasto-plastic State. If q equals limit load, the slope is in the limit equilibrium state. The slope may be divided into three zones. Some charts of the critical angle, the critical and limit load coefficients are presented in this paper.展开更多
文摘The randomness of strength and deformation of concrete material is serious and should be considered both in theoretical analyses such as Finite Element Methods and engineering practice, specially for those structural members with a uniform stress field, where stresses or strains are approximately the same under loading. A mathematical ap- proach of producing a series of random variables of the ultimate tensile strain in concrete is proposed to describe the randomness ofconcrete deformation. With reinforced concrete finite elements a real model calculation method is found for the randomness of initial cracks determined by a minimum tension strain within the uniform stress fields of concrete members. The proposed methods in our paper have as aim to improve the existing method used by FEM and other rela- tive approaches, which normally pay less attention to randomness with consequences that may possibly differ from testing or practice. The method and sample computation as indicated is meaningful and comply with testing and engi- neering practice.
基金Project supported by the National Natural Science Foundation of China(Nos.11902147,11872203,and 51921003)the Natural Science Foundation of Jiangsu Province of China(No.BK20190393)and the Natural Sciences and Engineering Research Council of Canada(No.RGPIN–2017-03716115112)。
文摘The identification of multiple interacting inclusions with uniform internal stresses in an infinite elastic matrix subjected to a uniform remote loading is of fundamental importance in the mechanics and design of particulate composite materials.In anti-plane shear and plane deformations,certain sufficient conditions have been established in the literature which guarantee uniform internal stresses inside multiple interacting inclusions displaying various symmetries when the matrix is subjected to specific uniform remote loading.Correspondingly,sufficient conditions which allow for the design of multiple interacting inclusions independent of any specific form of(uniform)remote loading have also been established.In this paper,we demonstrate rigorously that,in all cases,these sufficient conditions are also necessary conditions and indeed allow for the identification of all possible collections of such inclusions.
文摘The damage variables of describing the material damage state should be chosen first when the research of concrete structures by use of theory of damage theory. The method of calculation of damage parameter by the measure of the change of the elastic modulus of concrete specimens is effectively. In this paper, the wedge splitting tests with double bearing of three groups of different initial crack lengths of concrete specimens were conducted, and the stress and the strain of the points with different distance from the initial crack tip measured and calculated, and the damage value with peak stress of the various points were calculated based on the stress-strain curves. From the results of the test, the damage parameter can be confirmed under the non-uniform stress field, and the initial crack length has some influence on the damage parameter, and the longer the initial crack length and the greater the damage parameter.
文摘This paper provides a review of recent research advances and trends in the area of stability of unstiffened circular cylindrical shells subjected to general non-uniform axial compressive stresses.Only the more important and interesting aspects of the research,judged from a personal viewpoint,are discussed.They can be crudely classified into four categories:(1) shells subjected to non-uniform loads;(2) shells on discrete supports;(3) shells with intended cutouts/holes;and (4) shells with non-uniform settlements.
基金Supported by National Natural Science Foundation of China (No. 50490274,10472134).
文摘Based on the characteristics of 1D waves,the stress uniformity process in specimens under different loading conditions of rectangular and half-sine input waves was analyzed in split Hopkinson pressure bar (SHPB) test.The results show that the times of an elastic wave propa-gating from one end to the other in a specimen to attain stress equilibrium,is related to input wave-forms and relative mechanical impedance between the specimen and the input/output bars.Here-into,with the increae of the relative impedance,the times decreases under rectangular input waves loading,while it increases under half-sine input wave loading.The dimensionless stress value of specimen corresponding to the status of stress equilibrium increases with the increase of the rela-tive mechanical impedance.However,the dimensionless stress value under half-sine input wave loading is significantly lower than the value under rectangular input wave loading for specimen with low mechanical impedance,and the relative differentia of the dimensionless stress values under two loading conditions decreases with the increase of the relative mechanical impedance.In gen-eral,the forced state of specimen with relatively low mechanical impedance under half-sine input wave loading is evidently superior to the state under rectangular input wave loading in SHPB test,and the advantages of forced state under half-sine input wave loading turns weak with the increase of the relative mechanical impedance.
基金support from the National 973 Program (Grant No. 2006CB705808)PetroChina Young and Middle Aged People Innovation Fund (Grant No. 07E1016)+1 种基金PetroChina Science & Technology Innovation Fund (Grant No. 2008D-5006-02-09)Science & Technology Innovation Fund of Southwest Petroleum University (Grant No. 2007XJZ010)
文摘In view of the anisotropy,heterogeneity and stress-sensitive permeability in low permeability reservoirs,an analytical well test model was established by introducing the concept of permeability modulus.This model considered the permeability stress-sensitivity,wellbore storage effect,and the skin effect.The perturbation technique and Laplace transformation were used to solve the mathematical model analytically in Laplace space,and the bottom-hole pressure type curves were plotted and analyzed in real space by using the Stehfest numerical inversion.
文摘An essential problem in the design of mechanical impact systems is the impact of a piston on a rod. The impact of a semi finite cylindrical piston on a non uniform rod was studied. Based on wave mechanics and characteristic line theory, an inverse numerical approach to determine the piston profile was proposed, by means of which the geometry of an impact piston may be determined from the given stress waveform for a given rod profile. Numerical results show that the given stress waveform may be produced by means of the alternatives of design of piston and rod. There is good agreement between the experimental results and numerical results. [
文摘Current methodologies used for the inference of thin film stress through curvature measurements are strictly restricted to stress and curvature states which are assumed to remain uniform over the entire film/substrate system. By considering a circular thin film/substrate system subject to non-uniform, but axisymmetric misfit strain distributions in the thin film, we derived relations between the film stresses and the misfit strain, and between the plate system＇s curvatures and the misfit strain. These relations feature a “local” part which involves a direct dependence of the stress or curvature components on the misfit strain at the same point, and a “non-local” part which reflects the effect of misfit strain of other points on the location of scrutiny. Most notably, we also derived relations between the polar components of the film stress and those of system curvatures which allow for the experimental inference of such stresses from full-field curvature measurements in the presence of arbitrary radial non-uniformities. These relations also feature a “non-local” dependence on curvatures making a full-field measurement a necessity. Finally, it is shown that the interfacial shear tractions between the film and the substrate are proportional to the radial gradients of the first curvature invariant and can also be inferred experimentally.
文摘According to the Mohr-Coulomb yield criterion, the stress field of the infinite slope is derived under a vertical uniform load q on the top of the slope. It is indicated that elastic and elasto-plastic states would occur in the slope. When q is smaller than the critical load, q(p), the slope is in the elastic state. If q equals q(p), the slope is in the critical state, and the plastic deformation would occur along the critical angle. With the increase of q, the plastic zone would extend, and the slope is in the elasto-plastic State. If q equals limit load, the slope is in the limit equilibrium state. The slope may be divided into three zones. Some charts of the critical angle, the critical and limit load coefficients are presented in this paper.
