Papers by Keyword: Contact Length

Abstract: Accurate characterization of low-resistance ohmic contacts on 4H-SiC is crucial for devicedevelopment, but is complicated by the limitations of the standard Transfer Length Method (TLM).TLM test structures are widely used for extracting the specific contact resistivity (ρC) between metaland semiconductor layers, as well as the sheet resistance of doped layers. The contact formation pro-cess itself, particularly the annealing step, modifies the SiC layer under the contact. This results in asheet resistance below the contact (RSK) that deviates from the sheet resistance of interest between thecontacts (RSH), which invalidates a key assumption of the standard TLM evaluation of a constant RSHthroughout the whole TLM test structure. This study uses 2D TCAD simulation of TLM test structuresto investigate the influence of the contact length L, while using an advanced evaluation method forextracting ρC with the help of a third contact. Consequently, it is necessary to measure the contactend resistance RCE, which is derived from the potential at the end of the TLM contact. The findingsprovide a deeper understanding of the TLM technique’s robustness and offer valuable guidelines foroptimizing TLM test structures to ensure accurate characterization of ohmic contacts on 4H-SiC.

Abstract: The current trend in temper rolling is to make a small reduction to steel strip in order to achieve higher strength with good formability and toughness. In addition, very high strength steels can be cold rolled twice with very small reductions. This causes problems in setup values for cold rolling. Rolling models are usually overestimating roll flattening in the case of small reductions.In temper rolling thickness reduction is small (0.5 – 3%) and the elastic deformation of the work roll should be taken into account [3]. However, standard circular arc roll gap models (e.g. Bland Ford Ellis combined with Hitchcock model) fail to predict the roll flattening and thus the rolling force [4]. In this work, finite element method has been used to define a simplified model for work roll flattening and contact length. Model describes the effect of reduction, strength of steel strip and roll radius.

Abstract: Rocking motion wire saw with the additional rocking motion of either the wire or the workpiece is a new machining method compared with the traditional wire saw. The length of contact between the wire and the workpiece changes in this new saw process. In this paper, the wire motion and the contact length were theoretically researched. Wire motion path equation with the rocking motion was established. The theoretical equation of the contact length in half a swing period was derived out. The results indicated that the wire motion was a single pendulum movement with a length line segment, which the swing pivot was moved with a feed rate. The contact length had significant changes in half a swing period in the rocking motion wire saw. The contact length varied periodically with the same amplitude in the square ingot sawing, which varied periodically with the variation amplitude in the circle ingot sawing. The contact length with the rocking motion was obviously shorter than the case without the rocking motion for either the square ingot or the circle ingot.

Abstract: In order to better reveal the theoretical nature of internal ultrasonic grinding which is an efficient grinding technology, the characteristics of grits motion is analyzed under axial vibration and the grits kinematic equation is established. By using Matlab the single particles trajectory is simulated, then the displacement of a grit is given at any time they contact. Through the theoretical analysis and Matlab simulation, we can achieve that for axial ultrasonic vibration the influences of axial feed on the grits trajectory is too litter to be ignored. So when calculate the contact length of the grinding wheel and the work piece, the grinding wheels axial feed can be neglected. Then the contact length of the grinding wheel and the work piece is achieved. It has a significant value for simplifying the calculation of the grinding force and the analysis of internal ultrasonic grinding.

Abstract: Heat generated in machining is significant to study, as number of technical and economic problems has root into it. The high temperatures on cutting tool needs better understanding of contact processes at tool-chip ,tool-workpiece interfaces. The contact length at tool-chip interface is significant to study as it governs the heat moving to the tool as well as many tribological conditions like stresses, tool wear. Understanding of Tool-workpiece interface is significant as it affects the heat moving to workpiece, tool, chip as well as tool flank wear and major machined surface characteristics. Non-sliding type tool wear mechanisms which are highly sensitive to temperature changes are important to study. The latest trends of using High Speed Machining, Dry and Near Dry Machining, Finish hard turning results in more heat generation demanding significant understanding of effect of heat generated and temperatures.

Abstract: It is considered that the contact stiffness between the grinding wheel and the workpiece depends on the number of the abrasive grains in contact with the workpiece and the support stiffness of a single abrasive grain. In this paper, the calculating method of the theoritical contact stiffness of grinding wheel in grinding operation was proposed. Comparing calculated results of the contact stiffness in grinding operation with measured it in the stationary state, the contact stiffness of the grinding wheel in grinding operation was investigated.

Abstract: This paper analyzes theoretically the contact length derived from elastic-plastic mechanics and microcontact theory with the aim of improving the traditional method of predicting roughness factor though experiments. The accuracy of the analysis is verified through experiments. It transpires from the theoretical model that the contact length between a grinding wheel and a workpiece increases with decreasing curvature radius of peak, increasing hardness of the workpiece as well as increasing depth of cut. It is also revealed that the contact length is directly proportional to the square of 0.32 of the hardness, approximately, whilst the square root of surface roughness and the density of peak of the grinding wheel show less influence on the contact length. The analysis method has reduced the variation between predicted and experimental values than that of the old methods. These results will be beneficial in analysing and designing the product quality of grinding.

Abstract: Due to the complexity of the actual rolling process, asymmetrical conditions of deformation zone can cause front end bending or lead to poor shape, profile or quality of the product, as well as reducing productivity. Therefore it is important to study the geometric parameters of deformation zone in order to determine the work parameters accurately during rolling. Because the stock is often inclined when it enters the rolls, the deformation zone is asymmetrical. In this investigation, a model of calculating contact length between stock and roll precisely is deduced according to the theory of rolling. The results by theoretical calculation and experiment prove that the projected arc is raised while the stock enters the rolls serious asymmetrically, as well as the increase of the entrance thickness of the rolling stock and the decrease of the exit thickness of the rolled stock.

Abstract: Although forming of porous metal is demanded for industrial applications, the deformation characteristics have not been investigated sufficiently. In this study, lotus-type porous copper is processed by multi-pass cold rolling. At the early stage of rolling, the elongation of the porous copper in the rolling direction is small, and the porosity decreases almost linearly with the total reduction in thickness. It is found that pass schedule with small rolls and with small reduction per pass is effective to suppress pore closure. Hardness of the porous copper increases almost linearly with total reduction. If the effective total reduction is considered, the hardness change is similar to that of a nonporous copper.

Abstract: This paper presents a stress analysis of the ceramic femoral heads of hip joint prostheses with different borehole shapes to evaluate their mechanical reliability in terms of stress concentration. Under the ideal loading conditions used for ceramic rupture tests specified by the ISO 7206-5 standard, a finite element (FE) modeling is performed to determine the tensile and hoop stress distributions in the ceramic femoral heads. Two borehole shapes that are currently used in the manufacturing industry for hip joint prostheses, namely the flat bottom and keyhole, were first studied. Two new borehole shapes, dome arc and dome ellipse, were then introduced by the authors in the paper to minimize the stress concentration. It was found that while the currently used borehole shapes lead to high tensile notch stresses at their critical corners causing possible fracture failure of ceramic heads, the authors’ borehole designs can improve the mechanical reliability significantly. In addition, the effects of taper-bore contact length and their interface friction are investigated and discussed.