天然气水合物以胶结及孔隙填充等形式存在于深海能源土中,开采时因其分解会劣化地层力学特性进而引发海底事故,使得人们对能源土开采过程进行中力学特性的变化愈发重视。在前期室内试验的基础上,将一个温度-水压-力学二维微观胶结模型...天然气水合物以胶结及孔隙填充等形式存在于深海能源土中,开采时因其分解会劣化地层力学特性进而引发海底事故,使得人们对能源土开采过程进行中力学特性的变化愈发重视。在前期室内试验的基础上,将一个温度-水压-力学二维微观胶结模型引入离散元商业软件PFC2D中,通过对排气、排水性较好的土体进行升温及降压法开采进行数值模拟,并将模拟结果与相同条件下的室内试验结果对比,验证了该胶结模型的适用性。进一步分析了颗粒接触分布与颗粒平均纯转动率(averaged pure rotation rate,APR)在水合物分解时的变化情况。升温分解过程中随温度升高,颗粒总接触分布各向异性程度增大;胶结接触逐渐减少并始终保持主方向为水平方向,无胶结接触增多并始终保持主方向为竖直方向;APR值逐渐增大且正负值分布逐渐趋于集中。降压分解过程中随反(水)压降低,颗粒总接触由各向同性分布逐渐发展为主方向为竖直方向的各向异性,APR值较小且分布均匀;恢复反压后,试样进一步破坏,颗粒总接触各向异性更加明显,APR值增大且正负值呈集中分布。展开更多
Three kinds of welds were made using low frequency pulse current variable polarity tungsten inter gas （LPVPTIG） with argon shielding, direct current TIG （DCTIG） with helium shielding and high frequency pulse curr...Three kinds of welds were made using low frequency pulse current variable polarity tungsten inter gas （LPVPTIG） with argon shielding, direct current TIG （DCTIG） with helium shielding and high frequency pulse current variable polarity TIG （HPVPTIG） with argon shielding, respectively. It was found that macrosegregation bands with large amount of thick continuous eutectics and microporosities formed in the LPVPTIG weld due to the fluctuation of the pulse varied heat input. Only microsegregation existed in the DCTIG weld and HPVPTIG weld. However,the HPVPTIG weld had lower extent of Cu microsegregation since its welding speed was slower. The tensile results indicated that the mechanical properties of the weld decreased with the increase of the segregation extent of Cu and porosities, and LPVPTIG weld had lower tensile properties in the longitudinal direction than those in the transverse direction due to the macrosegregation bands.展开更多
Nonequilibrium statistical theory of fracture is a theory of fracture that macromechanical quantities can be derived from the microscopic atomic mechanism of microcrack(or microvoid)evolution kinetcs by means of noneq...Nonequilibrium statistical theory of fracture is a theory of fracture that macromechanical quantities can be derived from the microscopic atomic mechanism of microcrack(or microvoid)evolution kinetcs by means of nonequilibrium statistical physical concepts and methods. The microcrack evolution equation is the central equation in the theory.The coefficents of the equation, the microcrack growth rate and the microcrack nucleation rate,come from microscopic atomic mechanism.The solution of the equation connects with macromechanical quantities by the model of the weakest chain. All the other formulas and quantities, for instance, distribution function,fracture probability, reliability, failure rate and macromechanical quantities such as strength, toughness, life etc. and their statistical distribution function and statistical fluctuation are derived in a unified fashion and expressed by a few physical parameters. This theory can be widely applied to various kinds of fracture, such as the brittle, fatigue, delayed and environmental fracture of metals and structural ceramics. The theoretical framework of this theory is given in this paper.展开更多
The relationships between microhardness and microstructure, macrostructure and mechanical properties of friction stir welded joints AA6061-T913 were studied. Three equations were suggested to predict the grain size, u...The relationships between microhardness and microstructure, macrostructure and mechanical properties of friction stir welded joints AA6061-T913 were studied. Three equations were suggested to predict the grain size, ultimate tensile strength and yield strength from the hardness throughout the weld. Two-dimensional contour of grain size and three-dimensional maps of ultimate tensile and yield strengths were plotted according to the proposed equations. Also, the location of macroscopic zones was estimated based on hardness distribution. The modeling results were compared with the results obtained from microscopy and tensile tests. The modeling results show good agreement with the experimental findings, and the average differences between them for the ultimate tensile strength and yield strength were about 8% and 3%, respectively.展开更多
Based on parameter design language, a program of progressive failure analysis in composite structures is proposed. In this program, the relationship between macro- and micro-mechanics is established and the macro stre...Based on parameter design language, a program of progressive failure analysis in composite structures is proposed. In this program, the relationship between macro- and micro-mechanics is established and the macro stress distribution of the composite structure is calculated by commercial finite element software. According to the macro-stress, the damaged point is found and the micro-stress distribution of representative volume element is calculated by finite-volume direct averaging micromechanics(FVDAM). Compared with the results calculated by failure criterion based on macro-stress field(the maximum stress criteria and Hashin criteria) and micro-stress field(Huang model), it is proven that the failure analysis based on macro- and micro-mechanics model is feasible and efficient.展开更多
文摘天然气水合物以胶结及孔隙填充等形式存在于深海能源土中,开采时因其分解会劣化地层力学特性进而引发海底事故,使得人们对能源土开采过程进行中力学特性的变化愈发重视。在前期室内试验的基础上,将一个温度-水压-力学二维微观胶结模型引入离散元商业软件PFC2D中,通过对排气、排水性较好的土体进行升温及降压法开采进行数值模拟,并将模拟结果与相同条件下的室内试验结果对比,验证了该胶结模型的适用性。进一步分析了颗粒接触分布与颗粒平均纯转动率(averaged pure rotation rate,APR)在水合物分解时的变化情况。升温分解过程中随温度升高,颗粒总接触分布各向异性程度增大;胶结接触逐渐减少并始终保持主方向为水平方向,无胶结接触增多并始终保持主方向为竖直方向;APR值逐渐增大且正负值分布逐渐趋于集中。降压分解过程中随反(水)压降低,颗粒总接触由各向同性分布逐渐发展为主方向为竖直方向的各向异性,APR值较小且分布均匀;恢复反压后,试样进一步破坏,颗粒总接触各向异性更加明显,APR值增大且正负值呈集中分布。
文摘Three kinds of welds were made using low frequency pulse current variable polarity tungsten inter gas （LPVPTIG） with argon shielding, direct current TIG （DCTIG） with helium shielding and high frequency pulse current variable polarity TIG （HPVPTIG） with argon shielding, respectively. It was found that macrosegregation bands with large amount of thick continuous eutectics and microporosities formed in the LPVPTIG weld due to the fluctuation of the pulse varied heat input. Only microsegregation existed in the DCTIG weld and HPVPTIG weld. However,the HPVPTIG weld had lower extent of Cu microsegregation since its welding speed was slower. The tensile results indicated that the mechanical properties of the weld decreased with the increase of the segregation extent of Cu and porosities, and LPVPTIG weld had lower tensile properties in the longitudinal direction than those in the transverse direction due to the macrosegregation bands.
文摘Nonequilibrium statistical theory of fracture is a theory of fracture that macromechanical quantities can be derived from the microscopic atomic mechanism of microcrack(or microvoid)evolution kinetcs by means of nonequilibrium statistical physical concepts and methods. The microcrack evolution equation is the central equation in the theory.The coefficents of the equation, the microcrack growth rate and the microcrack nucleation rate,come from microscopic atomic mechanism.The solution of the equation connects with macromechanical quantities by the model of the weakest chain. All the other formulas and quantities, for instance, distribution function,fracture probability, reliability, failure rate and macromechanical quantities such as strength, toughness, life etc. and their statistical distribution function and statistical fluctuation are derived in a unified fashion and expressed by a few physical parameters. This theory can be widely applied to various kinds of fracture, such as the brittle, fatigue, delayed and environmental fracture of metals and structural ceramics. The theoretical framework of this theory is given in this paper.
基金The support of Iran National Science Foundation(INSF)(Grant No.91051732)
文摘The relationships between microhardness and microstructure, macrostructure and mechanical properties of friction stir welded joints AA6061-T913 were studied. Three equations were suggested to predict the grain size, ultimate tensile strength and yield strength from the hardness throughout the weld. Two-dimensional contour of grain size and three-dimensional maps of ultimate tensile and yield strengths were plotted according to the proposed equations. Also, the location of macroscopic zones was estimated based on hardness distribution. The modeling results were compared with the results obtained from microscopy and tensile tests. The modeling results show good agreement with the experimental findings, and the average differences between them for the ultimate tensile strength and yield strength were about 8% and 3%, respectively.
基金Project(51075204)supported by the National Natural Science Foundation of ChinaProjects(2012ZB52026,2014ZB52024)supported by the Aeronautical Science Foundation of ChinaProject(NS2014024)supported by the Fundamental Research Funds for the Central Universities,China
文摘Based on parameter design language, a program of progressive failure analysis in composite structures is proposed. In this program, the relationship between macro- and micro-mechanics is established and the macro stress distribution of the composite structure is calculated by commercial finite element software. According to the macro-stress, the damaged point is found and the micro-stress distribution of representative volume element is calculated by finite-volume direct averaging micromechanics(FVDAM). Compared with the results calculated by failure criterion based on macro-stress field(the maximum stress criteria and Hashin criteria) and micro-stress field(Huang model), it is proven that the failure analysis based on macro- and micro-mechanics model is feasible and efficient.
