在环境污染日益严重的今天,汽车轻量化已成为当今社会亟待解决的问题,而钢/铝异种金属的焊接结构正是实现汽车轻量化的有效手段之一。激光焊具有焊接速度快、能量密度高、焊接变形小等特点,因此采用激光焊对钢/铝异种金属进行焊接。研...在环境污染日益严重的今天,汽车轻量化已成为当今社会亟待解决的问题,而钢/铝异种金属的焊接结构正是实现汽车轻量化的有效手段之一。激光焊具有焊接速度快、能量密度高、焊接变形小等特点,因此采用激光焊对钢/铝异种金属进行焊接。研究结果表明,当焊接速度为20 mm/s、焊接功率为0.82~0.83 k W时,采用"钢上铝下"的搭接形式可获得成形良好的焊接接头。未添加中间层的接头界面处存在连续分布的及岛状的金属间化合物区,其组织主要为Fe_3Al、FeAl、FeAl_2、Fe_2Al_5和FeAl_3,其中部分FeAl_3呈针状形貌。添加Fe-B-Si中间层的钢/铝界面金属间化合物区边界趋于平整,厚度减少,且岛状区和针状FeAl_3数量减少。通过拉剪试验证明,Fe-B-Si中间层的添加可提高接头的力学性能。展开更多
The structure of fractures in nature rock appears irregular and induces complicated seepage flow behavior.The mechanism and quantitative description of fluid flow through rock fractures is a difficult subject that has...The structure of fractures in nature rock appears irregular and induces complicated seepage flow behavior.The mechanism and quantitative description of fluid flow through rock fractures is a difficult subject that has been greatly concerned in the fields of geotechnical,mining,geological,and petroleum engineering.In order to probe the mechanism of fluid flow and the effects of rough structures,we conducted a few laboratory tests of fluid flow through single rough fractures,in which the Weierstrass-Mandelbrot fractal function and PMMA material were employed to produce the fracture models with various fractal roughnesses.A high-speed video camera was employed to record the fluid flow through the entire single rough fracture with a constant hydraulic pressure.The properties of fluid flow varying with the fracture roughness and the influences of the rough structure were analyzed.The components of flow resistance of a single rough fracture were discussed.A fractal model was proposed to relate the fluid resistance to the fracture roughness.A fractal equivalent permeability coefficient of a single rough fracture was formulated.This study aims to provide an experimental basis and reference for better understanding and quantitatively relating the fluid flow properties to the structures of rock fractures.展开更多
文摘在环境污染日益严重的今天,汽车轻量化已成为当今社会亟待解决的问题,而钢/铝异种金属的焊接结构正是实现汽车轻量化的有效手段之一。激光焊具有焊接速度快、能量密度高、焊接变形小等特点,因此采用激光焊对钢/铝异种金属进行焊接。研究结果表明,当焊接速度为20 mm/s、焊接功率为0.82~0.83 k W时,采用"钢上铝下"的搭接形式可获得成形良好的焊接接头。未添加中间层的接头界面处存在连续分布的及岛状的金属间化合物区,其组织主要为Fe_3Al、FeAl、FeAl_2、Fe_2Al_5和FeAl_3,其中部分FeAl_3呈针状形貌。添加Fe-B-Si中间层的钢/铝界面金属间化合物区边界趋于平整,厚度减少,且岛状区和针状FeAl_3数量减少。通过拉剪试验证明,Fe-B-Si中间层的添加可提高接头的力学性能。
基金supported by the National Science Funds for Distinguished Young Scholar of China (Grant No. 51125017)the National Basic Research Program of China (Grant Nos. 2010CB226804,2011CB201201)+2 种基金the National Natural Science Foundation of China (Grant No. 50974125)the International Cooperation Project of Ministry of Science & Technology of China (Grant No. 2012DFA60760-2)NSFC International Cooperation and Exchange Program (Grant No. 51120145001)
文摘The structure of fractures in nature rock appears irregular and induces complicated seepage flow behavior.The mechanism and quantitative description of fluid flow through rock fractures is a difficult subject that has been greatly concerned in the fields of geotechnical,mining,geological,and petroleum engineering.In order to probe the mechanism of fluid flow and the effects of rough structures,we conducted a few laboratory tests of fluid flow through single rough fractures,in which the Weierstrass-Mandelbrot fractal function and PMMA material were employed to produce the fracture models with various fractal roughnesses.A high-speed video camera was employed to record the fluid flow through the entire single rough fracture with a constant hydraulic pressure.The properties of fluid flow varying with the fracture roughness and the influences of the rough structure were analyzed.The components of flow resistance of a single rough fracture were discussed.A fractal model was proposed to relate the fluid resistance to the fracture roughness.A fractal equivalent permeability coefficient of a single rough fracture was formulated.This study aims to provide an experimental basis and reference for better understanding and quantitatively relating the fluid flow properties to the structures of rock fractures.
