The effect of freeze-thaw(F-T)cycles on the mechanical behaviors and internal mechanism of rock mass is a critical research topic.In permafrost or seasonally frozen regions,F-T cycles have adverse effects on the mecha...The effect of freeze-thaw(F-T)cycles on the mechanical behaviors and internal mechanism of rock mass is a critical research topic.In permafrost or seasonally frozen regions,F-T cycles have adverse effects on the mechanical properties of rock mass,leading to many serious disasters in mining and geotechnical operations.In this paper,uniaxial compression tests are carried out on cyan sandstone after different F-T cycles.The failure modes and damage evolution of cyan sandstone under F-T cycles are studied.In addition,from the perspective of fracture and pore volume,the calculation equations of rock strain under frost heaving pressure and F-T cycles are established and verified with the corresponding laboratory tests.Subsequently,based on the classical damage theory,the F-T damage variables of cyan sandstone under different F-T cycles are calculated,and the meso-damage calculation model of cyan sandstone under F-T-loading coupling conditions is derived.Furthermore,through the discrete element numerical simulation software(PFC^(3D)),the microscopic damage evolution process of cyan sandstone under uniaxial compression after F-T cycles is studied,including the change of microcracks number,distribution of microcracks,and the acoustic emission(AE)count.The goal of this study is to investigate the damage evolution mechanism of rock from the mesoscopic and microscopic aspects,which has certain guiding value for accurately understanding the damage characteristics of rock in cold regions.展开更多
The cracking patterns of a thin sheet with a pre-existing crack subjected to dynamic loading are numerically simulated to investigate the mechanism of crack branching by using the FEM method.Six numerical models were ...The cracking patterns of a thin sheet with a pre-existing crack subjected to dynamic loading are numerically simulated to investigate the mechanism of crack branching by using the FEM method.Six numerical models were set up to study the effects of load,tensile strength and heterogeneity on crack branching.The crack propagation is affected by the applied loads,tensile strength and heterogeneity.Before crack branching,the crack propagates by some distance along the direction of the pre-existing crack.For the materials with low heterogeneity,the higher the applied stress level is and the lower the tensile strength of the material is,the shorter the propagation distance is.Moreover,the branching angle becomes larger and the number of branching cracks increases.In the case of the materials with high heterogeneity,a lot of disordered voids and microcracks randomly occur along the main crack,so the former law is not obvious.The numerical results not only are in good agreement with the experimental observations in laboratory,but also can be extended to heterogeneity media.The work can provide a good approach to model the cracking and fracturing of heterogeneous quasi-brittle materials,such as rock,under dynamic loading.展开更多
The generation and development of microcracks of SiCp/Al materials in the machining process were researched, and the forming causes and mechanism of the cut surface morphology for ap=0.2 mm or ap=0.4 mm and at 2 m/min...The generation and development of microcracks of SiCp/Al materials in the machining process were researched, and the forming causes and mechanism of the cut surface morphology for ap=0.2 mm or ap=0.4 mm and at 2 m/min～10 m/min were systematically analyzed. The supporting and "floor"roles of aluminum are wake at a shallower cutting depth and a lower speed, the SiC particles are shed under the role of cutting force, and the microcrack size of cut surface is larger. With the increase in the cutting depth and the cutting speed, the cutting temperature increases, the supporting and "floor" roles of aluminum are enhanced, the shedding and fracture of the reinforcement particles are flexible under the action of the cutting force, the fracture of cutting transforms from brittle to ductile, and the expansion of microcrack on the entire surface tends to balance with a smaller size. A curve between the cutting force and the cutting speed was plotted, a microcrack form of the cut surface was given, and some theoretical basis is provided for the mechanical processing and the surface quality.展开更多
基金Projects(52474167,52104109)supported by the National Natural Science Foundation of ChinaProject(2022JJ40602)supported by the Natural Science Foundation of Hunan Province,China。
文摘The effect of freeze-thaw(F-T)cycles on the mechanical behaviors and internal mechanism of rock mass is a critical research topic.In permafrost or seasonally frozen regions,F-T cycles have adverse effects on the mechanical properties of rock mass,leading to many serious disasters in mining and geotechnical operations.In this paper,uniaxial compression tests are carried out on cyan sandstone after different F-T cycles.The failure modes and damage evolution of cyan sandstone under F-T cycles are studied.In addition,from the perspective of fracture and pore volume,the calculation equations of rock strain under frost heaving pressure and F-T cycles are established and verified with the corresponding laboratory tests.Subsequently,based on the classical damage theory,the F-T damage variables of cyan sandstone under different F-T cycles are calculated,and the meso-damage calculation model of cyan sandstone under F-T-loading coupling conditions is derived.Furthermore,through the discrete element numerical simulation software(PFC^(3D)),the microscopic damage evolution process of cyan sandstone under uniaxial compression after F-T cycles is studied,including the change of microcracks number,distribution of microcracks,and the acoustic emission(AE)count.The goal of this study is to investigate the damage evolution mechanism of rock from the mesoscopic and microscopic aspects,which has certain guiding value for accurately understanding the damage characteristics of rock in cold regions.
基金Project(50820125405)supported by the National Natural Science Foundation of ChinaProject(51121005)supported by the National Natural Science Foundation of China
文摘The cracking patterns of a thin sheet with a pre-existing crack subjected to dynamic loading are numerically simulated to investigate the mechanism of crack branching by using the FEM method.Six numerical models were set up to study the effects of load,tensile strength and heterogeneity on crack branching.The crack propagation is affected by the applied loads,tensile strength and heterogeneity.Before crack branching,the crack propagates by some distance along the direction of the pre-existing crack.For the materials with low heterogeneity,the higher the applied stress level is and the lower the tensile strength of the material is,the shorter the propagation distance is.Moreover,the branching angle becomes larger and the number of branching cracks increases.In the case of the materials with high heterogeneity,a lot of disordered voids and microcracks randomly occur along the main crack,so the former law is not obvious.The numerical results not only are in good agreement with the experimental observations in laboratory,but also can be extended to heterogeneity media.The work can provide a good approach to model the cracking and fracturing of heterogeneous quasi-brittle materials,such as rock,under dynamic loading.
文摘The generation and development of microcracks of SiCp/Al materials in the machining process were researched, and the forming causes and mechanism of the cut surface morphology for ap=0.2 mm or ap=0.4 mm and at 2 m/min～10 m/min were systematically analyzed. The supporting and "floor"roles of aluminum are wake at a shallower cutting depth and a lower speed, the SiC particles are shed under the role of cutting force, and the microcrack size of cut surface is larger. With the increase in the cutting depth and the cutting speed, the cutting temperature increases, the supporting and "floor" roles of aluminum are enhanced, the shedding and fracture of the reinforcement particles are flexible under the action of the cutting force, the fracture of cutting transforms from brittle to ductile, and the expansion of microcrack on the entire surface tends to balance with a smaller size. A curve between the cutting force and the cutting speed was plotted, a microcrack form of the cut surface was given, and some theoretical basis is provided for the mechanical processing and the surface quality.
