For the problem of hydraulic fracture propagation when weakening the hard roof in fully mechanized top-coal caving stope of ultra-thick coal seam, based on the stress arch theory and the fracture mechanics, a two-dime...For the problem of hydraulic fracture propagation when weakening the hard roof in fully mechanized top-coal caving stope of ultra-thick coal seam, based on the stress arch theory and the fracture mechanics, a two-dimensional model for hydraulic fracture of the roof in the stope was established to investigate the propagation laws of hydraulic fracture. The result shows that, after mining, the principal stress direction of overlaying rock deflects to form the stress arch, whose arrow height and arch thickness increase with the increase of the mining width and the side pressure coefficient. Within the influence range of stress arch, the hydraulic fracture in hard roof deflects towards the stope direction in the course of propagation and forms the ‘‘arch" fracture, which cuts off the roof below the fracture in a laminated way. The deflection angle of hydraulic fracture increases with the increase of the mining width, but decreases with the increase of the side pressure coefficient and the fractured horizon. This research can provide theoretical basis for the application of hydraulic fracturing method in the stope roof weakening.展开更多
The hybrid SiC foam-SiC particles/Al double interpenetrating composites to be used as the brake materials of high speed train were fabricated by squeeze casting technique. The influence of the type of matrix on the me...The hybrid SiC foam-SiC particles/Al double interpenetrating composites to be used as the brake materials of high speed train were fabricated by squeeze casting technique. The influence of the type of matrix on the mechanical properties and the fracture mechanism of the hybrid composites was investigated. The interface bond in the hybrid composites is good for the composites have the unique double interpenetrating structure. The ductile matrix resists the propagation of the microcracks in the struts. During the microcrack propagation process, the energy absorption and the fracture surface area are increased, which increases the ductility of the hybrid composites. The compressive strength of the hybrid composite reinforced by the SiC with the total volume fraction of 53% is 660 MPa, which is higher than that of traditional composite reinforced by single SiC particles.展开更多
The crimp feasibility of AZ31 Mg alloy wide plate responding to asymmetry and anisotropy at different temperatures was conducted by bending experiments and numerical simulation.Through the microstructural characterist...The crimp feasibility of AZ31 Mg alloy wide plate responding to asymmetry and anisotropy at different temperatures was conducted by bending experiments and numerical simulation.Through the microstructural characteristic,mechanical properties,EBSD and FEM analysis,the results indicated that{10-12}twins and pyramidal(a)slip were dominated at the inner surface layer of the plate,while prismatic and pyramidal(a)slips were controlled at the outer layer when bending at 100℃,and their quantity decreased as the temperature elevation and vanished at 200℃.The flexural deflection increased gradually with the augment of flexural temperature,while the fracture stress weakened.A large number of twins nucleated and grew in the coarse grain,causing major distribution proportion of high angular grain boundaries(HAGBs)at the compression part,which could improve its flexural properties and affect subsequent strain contours,twins and recrystallization distribution.The offset of the neutral layer declined from 1.4125 mm to 0.7261 mm with the temperature rising from 100℃to 250℃when bending,while it was concentrated on 0.0338-0.0481 mm when coiling,accounting for 0.26%-0.37%of the plate thickness.At last,the reel diameter descended with increasing the temperature and coiling rate.展开更多
基金Financial supports for this work,provided by the National Natural Science Foundation of China (No.51104191)the China Postdoctoral Science Foundation (2016M602655)the Program for Changjiang Scholars and Innovative Research Team in University of China (No.IRT13043)
文摘For the problem of hydraulic fracture propagation when weakening the hard roof in fully mechanized top-coal caving stope of ultra-thick coal seam, based on the stress arch theory and the fracture mechanics, a two-dimensional model for hydraulic fracture of the roof in the stope was established to investigate the propagation laws of hydraulic fracture. The result shows that, after mining, the principal stress direction of overlaying rock deflects to form the stress arch, whose arrow height and arch thickness increase with the increase of the mining width and the side pressure coefficient. Within the influence range of stress arch, the hydraulic fracture in hard roof deflects towards the stope direction in the course of propagation and forms the ‘‘arch" fracture, which cuts off the roof below the fracture in a laminated way. The deflection angle of hydraulic fracture increases with the increase of the mining width, but decreases with the increase of the side pressure coefficient and the fractured horizon. This research can provide theoretical basis for the application of hydraulic fracturing method in the stope roof weakening.
基金Projects(01306016, 01307148) supported by Key Laboratory of Ministry of Education for Conveyance and Equipment (East China Jiaotong University), ChinaProject(09497) supported by the Young Science Foundation of Jiangxi Provincial Education Office, ChinaProject(50765005) supported by the National Natural Science Foundation of China
文摘The hybrid SiC foam-SiC particles/Al double interpenetrating composites to be used as the brake materials of high speed train were fabricated by squeeze casting technique. The influence of the type of matrix on the mechanical properties and the fracture mechanism of the hybrid composites was investigated. The interface bond in the hybrid composites is good for the composites have the unique double interpenetrating structure. The ductile matrix resists the propagation of the microcracks in the struts. During the microcrack propagation process, the energy absorption and the fracture surface area are increased, which increases the ductility of the hybrid composites. The compressive strength of the hybrid composite reinforced by the SiC with the total volume fraction of 53% is 660 MPa, which is higher than that of traditional composite reinforced by single SiC particles.
基金the project from the National Key Research and Development Program of China(No.2016YFB0301104)the National Natural Science Foundation of China(No.51771043)the Program of Introducing Talents of Discipline Innovation to Universities 2.0(the 111 Project 2.0 of China,No.BP0719037)。
文摘The crimp feasibility of AZ31 Mg alloy wide plate responding to asymmetry and anisotropy at different temperatures was conducted by bending experiments and numerical simulation.Through the microstructural characteristic,mechanical properties,EBSD and FEM analysis,the results indicated that{10-12}twins and pyramidal(a)slip were dominated at the inner surface layer of the plate,while prismatic and pyramidal(a)slips were controlled at the outer layer when bending at 100℃,and their quantity decreased as the temperature elevation and vanished at 200℃.The flexural deflection increased gradually with the augment of flexural temperature,while the fracture stress weakened.A large number of twins nucleated and grew in the coarse grain,causing major distribution proportion of high angular grain boundaries(HAGBs)at the compression part,which could improve its flexural properties and affect subsequent strain contours,twins and recrystallization distribution.The offset of the neutral layer declined from 1.4125 mm to 0.7261 mm with the temperature rising from 100℃to 250℃when bending,while it was concentrated on 0.0338-0.0481 mm when coiling,accounting for 0.26%-0.37%of the plate thickness.At last,the reel diameter descended with increasing the temperature and coiling rate.
