Surrounding rocks at different locations are generally subjected to different stress paths during the process of deep hard rock excavation.In this study,to reveal the mechanical parameters of deep surrounding rock und...Surrounding rocks at different locations are generally subjected to different stress paths during the process of deep hard rock excavation.In this study,to reveal the mechanical parameters of deep surrounding rock under different stress paths,a new cyclic loading and unloading test method for controlled true triaxial loading and unloading and principal stress direction interchange was proposed,and the evolution of mechanical parameters of Shuangjiangkou granite under different stress paths was studied,including the deformation modulus,elastic deformation increment ratios,fracture degree,cohesion and internal friction angle.Additionally,stress path coefficient was defined to characterize different stress paths,and the functional relationships among the stress path coefficient,rock fracture degree difference coefficient,cohesion and internal friction angle were obtained.The results show that during the true triaxial cyclic loading and unloading process,the deformation modulus and cohesion gradually decrease,while the internal friction angle gradually increases with increasing equivalent crack strain.The stress path coefficient is exponentially related to the rock fracture degree difference coefficient.As the stress path coefficient increases,the degrees of cohesion weakening and internal friction angle strengthening decrease linearly.During cyclic loading and unloading under true triaxial principal stress direction interchange,the direction of crack development changes,and the deformation modulus increases,while the cohesion and internal friction angle decrease slightly,indicating that the principal stress direction interchange has a strengthening effect on the surrounding rocks.Finally,the influences of the principal stress interchange direction on the stabilities of deep engineering excavation projects are discussed.展开更多
A laboratory experimental program performed on Wuhan sandstones was presented under monotonic loading, partial cyclic loading during loading path and sine wave cyclic loading with different strain rates to compare uni...A laboratory experimental program performed on Wuhan sandstones was presented under monotonic loading, partial cyclic loading during loading path and sine wave cyclic loading with different strain rates to compare uniaxial compression strength and elastic properties (elastic modulus and Poisson ratio) under different conditions and influence of pore fluid on them. When the loading strain rates are 10^(-5), 10^(-4) and 10^(-3)/s, uniaxial compression strengths of dry sandstones are 82.3, 126.6 and 141.6 MPa, respectively, and that of water saturated sandstones are 70.5, 108.3 and 124.1 MPa, respectively. The above results show that the uniaxial compression strength increases with the increase of strain rate, however, variation of softening coefficient is insignificant. Under monotonic loading condition, tangent modulus increases with an increment of stress (strain) to a maximum value at a certain stress level, beyond which it starts to decline. Under the partial cyclic loading during loading path condition, unloading or reloading modulus is larger than loading modulus, and unloading and reloading moduli are almost constants with respect to stress level, especially unloading modulus. Under the sine wave cyclic loading condition, tangent modulus and Poisson ratio display asymmetric 'X' shape with various strain, and the average unloading modulus is larger than the average loading modulus.展开更多
Irregular honeycomb structures occur abundantly in nature and in man-made products,and are an active area of research.In this paper,according to the optimization of regular honeycomb structures,two types of irregular ...Irregular honeycomb structures occur abundantly in nature and in man-made products,and are an active area of research.In this paper,according to the optimization of regular honeycomb structures,two types of irregular honeycomb structures with both positive and negative Poisson’s ratios are presented.The elastic properties of irregular honeycombs with varying structure angles were investigated through a combination of material mechanics and structural mechanics methods,in which the axial deformation of the rods was considered.The numerical results show that axial deformation has a significant influence on the elastic properties of irregular honeycomb structures.The elastic properties of the structure can be considered by the enclosed area of the unit structure,the shape of the unit structure,and the elastic properties of the original materials.The elastic properties considering the axial deformation of rods studied in this study can provide a reference for other scholars.展开更多
This paper investigated the compressive mechanical properties of antitetrachiral honeycombs with different thickness ratios of ligament to cylinder.The deformation and energy absorption performance of the structures w...This paper investigated the compressive mechanical properties of antitetrachiral honeycombs with different thickness ratios of ligament to cylinder.The deformation and energy absorption performance of the structures were characterized by the cooperation of experimental and numerical methods.First,two types(small and large thickness ratios)of antitetrachiral honeycombs were manufactured by 3D printing.Then,the deformation mode,negative Poisson’s ratio(NPR)and crushing stress of the honeycombs were obtained experimentally.After that,a finite element(FE)model was established by using ABAQUS/Explicit,and the numerical model and method were validated.Based on experimental and numerical results,the X mode,double-parallel line mode and cylinder mode were obtained in the compressive deformation of the honeycomb with a small thickness ratio.The Bi-V mode,“e”mode and Z mode were obtained in the compressive deformation of the honeycomb with a large thickness ratio.The influence of the thickness ratio of ligament to cylinder was studied,and a thickness ratio of 1.625 was the critical value for the transformation of the antitetrachiral honeycomb deformation modes.展开更多
基金the financial support from the National Natural Science Foundation of China(Grant Nos.51839003 and 42207221).
文摘Surrounding rocks at different locations are generally subjected to different stress paths during the process of deep hard rock excavation.In this study,to reveal the mechanical parameters of deep surrounding rock under different stress paths,a new cyclic loading and unloading test method for controlled true triaxial loading and unloading and principal stress direction interchange was proposed,and the evolution of mechanical parameters of Shuangjiangkou granite under different stress paths was studied,including the deformation modulus,elastic deformation increment ratios,fracture degree,cohesion and internal friction angle.Additionally,stress path coefficient was defined to characterize different stress paths,and the functional relationships among the stress path coefficient,rock fracture degree difference coefficient,cohesion and internal friction angle were obtained.The results show that during the true triaxial cyclic loading and unloading process,the deformation modulus and cohesion gradually decrease,while the internal friction angle gradually increases with increasing equivalent crack strain.The stress path coefficient is exponentially related to the rock fracture degree difference coefficient.As the stress path coefficient increases,the degrees of cohesion weakening and internal friction angle strengthening decrease linearly.During cyclic loading and unloading under true triaxial principal stress direction interchange,the direction of crack development changes,and the deformation modulus increases,while the cohesion and internal friction angle decrease slightly,indicating that the principal stress direction interchange has a strengthening effect on the surrounding rocks.Finally,the influences of the principal stress interchange direction on the stabilities of deep engineering excavation projects are discussed.
基金Project(Z110510) supported by Opening Research Foundation of the Chinese Academy of Sciences Key Laboratory of Rock and Soil MechanicsProject(20060390473) supported by China Postdoctoral Science FoudationProject(40172084) supported by the National Natural Science Foundation of China
文摘A laboratory experimental program performed on Wuhan sandstones was presented under monotonic loading, partial cyclic loading during loading path and sine wave cyclic loading with different strain rates to compare uniaxial compression strength and elastic properties (elastic modulus and Poisson ratio) under different conditions and influence of pore fluid on them. When the loading strain rates are 10^(-5), 10^(-4) and 10^(-3)/s, uniaxial compression strengths of dry sandstones are 82.3, 126.6 and 141.6 MPa, respectively, and that of water saturated sandstones are 70.5, 108.3 and 124.1 MPa, respectively. The above results show that the uniaxial compression strength increases with the increase of strain rate, however, variation of softening coefficient is insignificant. Under monotonic loading condition, tangent modulus increases with an increment of stress (strain) to a maximum value at a certain stress level, beyond which it starts to decline. Under the partial cyclic loading during loading path condition, unloading or reloading modulus is larger than loading modulus, and unloading and reloading moduli are almost constants with respect to stress level, especially unloading modulus. Under the sine wave cyclic loading condition, tangent modulus and Poisson ratio display asymmetric 'X' shape with various strain, and the average unloading modulus is larger than the average loading modulus.
基金Supported by Fundamental Research Funds for the Central Universities(Grant No.310812161003)Natural Science Basic Research Plan in Shaanxi Province of China(Grant No.2016JM5035).
文摘Irregular honeycomb structures occur abundantly in nature and in man-made products,and are an active area of research.In this paper,according to the optimization of regular honeycomb structures,two types of irregular honeycomb structures with both positive and negative Poisson’s ratios are presented.The elastic properties of irregular honeycombs with varying structure angles were investigated through a combination of material mechanics and structural mechanics methods,in which the axial deformation of the rods was considered.The numerical results show that axial deformation has a significant influence on the elastic properties of irregular honeycomb structures.The elastic properties of the structure can be considered by the enclosed area of the unit structure,the shape of the unit structure,and the elastic properties of the original materials.The elastic properties considering the axial deformation of rods studied in this study can provide a reference for other scholars.
文摘This paper investigated the compressive mechanical properties of antitetrachiral honeycombs with different thickness ratios of ligament to cylinder.The deformation and energy absorption performance of the structures were characterized by the cooperation of experimental and numerical methods.First,two types(small and large thickness ratios)of antitetrachiral honeycombs were manufactured by 3D printing.Then,the deformation mode,negative Poisson’s ratio(NPR)and crushing stress of the honeycombs were obtained experimentally.After that,a finite element(FE)model was established by using ABAQUS/Explicit,and the numerical model and method were validated.Based on experimental and numerical results,the X mode,double-parallel line mode and cylinder mode were obtained in the compressive deformation of the honeycomb with a small thickness ratio.The Bi-V mode,“e”mode and Z mode were obtained in the compressive deformation of the honeycomb with a large thickness ratio.The influence of the thickness ratio of ligament to cylinder was studied,and a thickness ratio of 1.625 was the critical value for the transformation of the antitetrachiral honeycomb deformation modes.
