To clarify the effect of SnO2 particle size on the arc erosion behavior of AgSnO2 contact material, Ag?4%SnO2 (mass fraction) contact materials with different sizes of SnO2 particles were fabricated by powder metallur...To clarify the effect of SnO2 particle size on the arc erosion behavior of AgSnO2 contact material, Ag?4%SnO2 (mass fraction) contact materials with different sizes of SnO2 particles were fabricated by powder metallurgy. The microstructure of Ag?4%SnO2 contact materials was characterized, and the relative density, hardness and electrical conductivity were measured. The arc erosion of Ag?4%SnO2 contact materials was tested, the arc duration and mass loss before and after arc erosion were determined, the surface morphologies and compositions of Ag?4%SnO2 contact materials after arc erosion were characterized, and the arc erosion mechanism of AgSnO2 contact materials was discussed. The results show that fine SnO2 particle is beneficial for the improvement of the relative density and hardness, but decreases the electrical conductivity. With the decrease of SnO2 particle size, Ag?4%SnO2contact material presents shorter arc duration, less mass loss, larger erosion area and shallower arc erosion pits.展开更多
Adhesion has been demonstrated to play an important role in contact and friction between objects at small scales. While various models have been established for adhesive contact under normal forces, studies on the adh...Adhesion has been demonstrated to play an important role in contact and friction between objects at small scales. While various models have been established for adhesive contact under normal forces, studies on the adhesive contact under tangential force have been far fewer, which if any, are mostly confined to the non-slipping situations. In the present work, a model has been proposed for adhesive contact with local sliding under tangential forces. Herein, the onset of local sliding in adhesive contact has been addressed by assuming the nucleation of dislocations. By analogy with the emission of dislocations at a crack tip, the critical tangential force for the onset of sliding has been determined, and its effect on the evolution of contact size has also been studied. Comparison with relevant experiments has verified the validity of the present model.展开更多
In this article,we reviewed several existing techniques that were capable of detecting local temperatures in the range of 2000-3500 K in a contact manner.These techniques included several non-standard thermocouples,Se...In this article,we reviewed several existing techniques that were capable of detecting local temperatures in the range of 2000-3500 K in a contact manner.These techniques included several non-standard thermocouples,Seger cones and ultrasonic meters.In particular,ultrasonic meters made of tungsten(W)wires were proven to be working well in nuclear plant for detecting the central temperature of reaction zone.We also presented two alternative approaches.One of them was a kind of singlemetal-based thermal sensor made from W,Mo and Ta wires,which utilized the size effect of Seebeck coefficient and theoretically applicable in contact mode measurement up to 3500 K.The other was a kind of detectors with micro-/nano-patterns,which utilized the size effect of surface melting point of bulky materials.This work should shed light on measurement approaches for ultrahigh temperatures in a variety of practical applications.展开更多
Recently,super gas wet and gas wet surfaces have been extensively attended in petroleum industry,as supported by the increasing number of publications in the last decade related to wettability alteration in gas conden...Recently,super gas wet and gas wet surfaces have been extensively attended in petroleum industry,as supported by the increasing number of publications in the last decade related to wettability alteration in gas condensate reservoirs.In many cases,contact angle measurement has been employed to assess the wettability alteration.Even though contact angle measurement seems to be a straightforward approach,there exist many misuses of this technique and consequently misinterpretation of the corresponding results.In this regard,a critical inspection of the most recent updated concepts and the intervening parameters in the contact angle based wettability evaluation of liquid-solid-gas systems could aid to provide some remediation to alleviate this problem.To this end,this work presents a survey on the accurate terms and rigorous protocols based on the community of surface science and chemistry.As a preliminary step,advancing,receding,static,and the most stable contact angle terminology are defined.The study is followed by the definition of the contact angle hysteresis effect.The application of surface free energy in the selection of the best gas wet agent is then analyzed.Afterward,the impact of the size-dependent behavior of drop on contact angle is discussed.Finally,a sessile drop experiment is explained to achieve the defined parameters.For future contributions to petroleum industry journals,like this journal,this work could offer an easy use of the conceptual framework for analyzing the results and comparative evaluations in chemical wettability modifier agents.展开更多
车桥碰撞属于典型的非线性动力过程,采用理论方法通常难以求解。有限元方法(Finite element method,FEM)是研究车桥碰撞问题的重要工具,但其前处理过程涉及参数及算法众多,实际操作极其繁杂。为提升研究者建模效率,同时提高模型计算精度...车桥碰撞属于典型的非线性动力过程,采用理论方法通常难以求解。有限元方法(Finite element method,FEM)是研究车桥碰撞问题的重要工具,但其前处理过程涉及参数及算法众多,实际操作极其繁杂。为提升研究者建模效率,同时提高模型计算精度,提出一种精细化建模方法,该方法操作步骤为:1)以实际工程为背景,建立完整车辆-桥梁碰撞模型,并进行验证;2)进行网格敏感性分析,选择合适网格尺寸,取得计算效率与精度的平衡;3)对重力荷载进行初始加载,避免桥墩产生P-delta效应。研究结果表明:该精细化建模方法能较好地还原真实事故情况,并且碰撞过程满足能量守恒定律,沙漏能仅为总能量的2.3%;网格尺寸为35 mm和50 mm时桥墩的损伤情况、碰撞力和最大位移均比较接近,100 mm网格桥墩产生的碰撞力和最大位移偏大;ANSYS/LS-DYNA软件默认加载方式下的桥墩轴力呈现幅度较大的波动,最大轴力比预期轴力高75%,采取的重力初始化方法能够在一定程度上消除ANSYS/LS-DYNA软件的固有弊端,避免P-delta效应。该精细化建模方法能有效实现车桥碰撞模拟,并且能够取得良好的精度,可为未来的研究者提供建模思路,提升建模效率。展开更多
In this paper,the surface and cross-section,pore size and distribution,contact angle and hydrostatic pressure of the membrane were tested.Then the membrane's working principle was analyzed and the stopping height ...In this paper,the surface and cross-section,pore size and distribution,contact angle and hydrostatic pressure of the membrane were tested.Then the membrane's working principle was analyzed and the stopping height of membranes with different pore sizes was calculated.It was found that the surface tension and pore size of the membrane were key factors to determine its stopping height.展开更多
基金Project(51274163)supported by the National Natural Science Foundation of ChinaProject(13JS076)supported by the Key Laboratory Research Program of Shaanxi Province,China+1 种基金Project(2012KCT-25)supported by the Pivot Innovation Team of Shaanxi Electrical Materials and Infiltration Technique,ChinaProject(2011HBSZS009)supported by the Special Foundation of Key Disciplines,China
文摘To clarify the effect of SnO2 particle size on the arc erosion behavior of AgSnO2 contact material, Ag?4%SnO2 (mass fraction) contact materials with different sizes of SnO2 particles were fabricated by powder metallurgy. The microstructure of Ag?4%SnO2 contact materials was characterized, and the relative density, hardness and electrical conductivity were measured. The arc erosion of Ag?4%SnO2 contact materials was tested, the arc duration and mass loss before and after arc erosion were determined, the surface morphologies and compositions of Ag?4%SnO2 contact materials after arc erosion were characterized, and the arc erosion mechanism of AgSnO2 contact materials was discussed. The results show that fine SnO2 particle is beneficial for the improvement of the relative density and hardness, but decreases the electrical conductivity. With the decrease of SnO2 particle size, Ag?4%SnO2contact material presents shorter arc duration, less mass loss, larger erosion area and shallower arc erosion pits.
基金supported by the National Key Basic Research Program (No.2012CB937500)Natural Science Foundation of China (No.11572216)
文摘Adhesion has been demonstrated to play an important role in contact and friction between objects at small scales. While various models have been established for adhesive contact under normal forces, studies on the adhesive contact under tangential force have been far fewer, which if any, are mostly confined to the non-slipping situations. In the present work, a model has been proposed for adhesive contact with local sliding under tangential forces. Herein, the onset of local sliding in adhesive contact has been addressed by assuming the nucleation of dislocations. By analogy with the emission of dislocations at a crack tip, the critical tangential force for the onset of sliding has been determined, and its effect on the evolution of contact size has also been studied. Comparison with relevant experiments has verified the validity of the present model.
基金financially supported by National Key R&D Program of China(Nos.2016YFA0200802 and2017YFA0701302)
文摘In this article,we reviewed several existing techniques that were capable of detecting local temperatures in the range of 2000-3500 K in a contact manner.These techniques included several non-standard thermocouples,Seger cones and ultrasonic meters.In particular,ultrasonic meters made of tungsten(W)wires were proven to be working well in nuclear plant for detecting the central temperature of reaction zone.We also presented two alternative approaches.One of them was a kind of singlemetal-based thermal sensor made from W,Mo and Ta wires,which utilized the size effect of Seebeck coefficient and theoretically applicable in contact mode measurement up to 3500 K.The other was a kind of detectors with micro-/nano-patterns,which utilized the size effect of surface melting point of bulky materials.This work should shed light on measurement approaches for ultrahigh temperatures in a variety of practical applications.
文摘Recently,super gas wet and gas wet surfaces have been extensively attended in petroleum industry,as supported by the increasing number of publications in the last decade related to wettability alteration in gas condensate reservoirs.In many cases,contact angle measurement has been employed to assess the wettability alteration.Even though contact angle measurement seems to be a straightforward approach,there exist many misuses of this technique and consequently misinterpretation of the corresponding results.In this regard,a critical inspection of the most recent updated concepts and the intervening parameters in the contact angle based wettability evaluation of liquid-solid-gas systems could aid to provide some remediation to alleviate this problem.To this end,this work presents a survey on the accurate terms and rigorous protocols based on the community of surface science and chemistry.As a preliminary step,advancing,receding,static,and the most stable contact angle terminology are defined.The study is followed by the definition of the contact angle hysteresis effect.The application of surface free energy in the selection of the best gas wet agent is then analyzed.Afterward,the impact of the size-dependent behavior of drop on contact angle is discussed.Finally,a sessile drop experiment is explained to achieve the defined parameters.For future contributions to petroleum industry journals,like this journal,this work could offer an easy use of the conceptual framework for analyzing the results and comparative evaluations in chemical wettability modifier agents.
基金Supported by The Special Coordination Fund(SCF)for Pro-moting Science and Technology commissioned by the Ministry of Education,Culture,Sports,Science and Technology(MEXT)of Japan
文摘AIM: To verify the performance of a lesion size measurement system through a clinical study.
文摘In this paper,the surface and cross-section,pore size and distribution,contact angle and hydrostatic pressure of the membrane were tested.Then the membrane's working principle was analyzed and the stopping height of membranes with different pore sizes was calculated.It was found that the surface tension and pore size of the membrane were key factors to determine its stopping height.
