查看更多>>摘要：High-performance concrete (HPC) as a promising construction material has been widely used in infrastructures and high-rise buildings etc. However, its pretty high autogenous shrinkage (AS) especially in its early age becomes one of the key problems endangering long-time durability of HPC structures. This paper carried out the early age AS research of large scaled HPC column specimens by embedded Fiber Bragg-Grating (FBG) strain sensor. Temperature compensation for FBG strain sensor by thermocouple was also attempted in this paper, and the results were reasonable and acceptable comparing with the result compensated by FBG temperature sensor. Reinforcement influence, size effect and temperature effect on HPC AS were also analyzed respectively in this paper.
查看更多>>摘要：This study used the micro double cup extrusion of aluminum to investigate the effects of the surface roughness of workpiece and die on the tribological conditions involving mixed lubrication and plastic deformation. The aluminum billets with the diameter of 3 mm and the height of 4.5 mm in different surface roughnesses were prepared by grinding processes and used in the experiments under conditions of dry and molybdenum disulfide lubrication. To estimate the friction factors, the heights of the extruded cups were measured and compared with those predicted by finite element simulations using the law of constant shear stress. The results show that smaller workpiece surface roughness resulted in low and nearly constant friction in the early stage of the micro extrusion under the dry and lubricated conditions, which were reflected in the estimated friction factors. In the later stage of the extrusion processes, the workpiece surface finish became close to the one of the die for all tested conditions. The friction was clearly reduced in the dry condition but it became greater in the cases with the lubricated condition. The surface condition in the later stage of the micro extrusion process was believed to allow the lubricant to escape from the contact interface.
查看更多>>摘要：The main objective of this study is to investigate the effect of bearing preloads on the characteristics of spindle stiffness. Finite element model for spindle-bearing system is established enabling the variation of spindle stiffness calculations under different bearing preloads. On the other hand, the spindle stiffness may also be obtained from the experiment and its result may be utilized to validate the numerical calculations. The front-end section of spindle is acted by poise weights at different directions, and their corresponding deformations are measured through dial indicator. Three bearing preload conditions, i.e. light, medium and heavy preloads are selected, which are imposed on the bearing to investigate the spindle stiffness variation, respectively. In addition, the effects of the geometrical parallelism error at the end surfaces of spacer due to the manufacturing tolerance or some imperfection on the spindle stiffness are studied. Finally, the impact test on the spindle-bearing body is performed by hammer and the corresponding vibration signal on the spindle surfaces is acquired by aecelerometer. The spindle stiffness may be reflected in the other manner through the signals processing by spectrum analysis.
查看更多>>摘要：This paper concerns the design and analysis of a 6-DOF inverted Stewart platform of an amusement park. In consideration of both the thrill-seeking and the safety of tourists, the platform must have 3 proper translational axial accelerations and 3 proper rotary angular accelerations within one motion cycle, and the impact of seismic force shall be taken into account in order to retain the adaptability to change of the system in case of emergent situations. Besides, the safety factors of various parts and components of the system shall be higher than six. In this paper, a 3D model is developed for the platform by means of Solidwork, and kinematics simulation is carried out by means of Cosmos/Motion software to generate 3D geometrical diagrams which are to be transferred into ANSYS Workbench software, and at last, the optimized design of geometry of each part/component of the system and the evaluation of overall safety of the system are conducted in Workbench software based on foresaid 3D geometrical diagrams.
查看更多>>摘要：In this paper, a parametric cubic spline function for generating gear profile is proposed. The spline function includes new gear design parameters such as pressure angle, number of teeth, module, and tooth tip circle modification. The proposed geometry can improve corner filling condition. Finally, the simulation software DEFORM is used to simulate the cold forging process of the micro-gears with different profiles.
查看更多>>摘要：With rapid expansion of nanotechnology, microminiaturization has become imperative in the field of micro/nano fabrication. A nanomanipulation system with high degrees of freedom that can perform nanomachining, nanofabrication and mechanical/electrical characterization of nanoscale objects inside a scanning electron microscope (SEM) is presented. The manipulation system consists of several individual operating units each having three linear stages and one rotational stage. The body of the manipulator is designed using the idea of superposition. Each operating unit can move in the permissible range of SEM's vacuum chamber and can increase or decrease the number of units according to the requirement. Experiments were executed to investigate the in-situ electrical resistance of nano materials.
查看更多>>摘要：This paper presents an integrated process of structural topology optimization in minimizing both compliance and structural weight. The material volume fraction acts an additional design variable subjected to the empirical approximate stress constraint in terms of material volume fraction. This explicitly approximate function can provide a convenient way to calculate its gradient information for numerical optimization. An engineer does not require advanced topology optimization and superior finite element technique in applying proposed method.
查看更多>>摘要：In order to inspect on wall condition inside the coke oven, an inspection device has been developed to protect a camera inside and sustains high temperature long enough so that it can be permanently-installed on the pusher ram beam. The temperature of the coking chamber during operation is about 1200 ℃ while the maximum tolerable temperature of a camera is less than 40 ℃. The device has to function as a good thermal insulator with cooling element for the camera at the pusher head and for signal cables along the beam. In this paper, the necessary conditions of the inspective device were found out by building a three-dimensional numerical model of the device to simulate the temperature distribution inside the device with CFD commercial software.
查看更多>>摘要：Thermoelectric coolers are often used in freezing chuck to freeze or to thaw easy broken egg-shells, clays, and other ferrous/nonferrous materials, which are incapable to machine it by other clamping technology. For design and application purposes, detailed studies of freezing/thawing processes by thermoelectric coolers are inevitable to the success of this technology. In this study, an experiment to measure the thermal resistance of single thermoelectric device is conducted and a model to calculate its hot and cold side temperatures is derived. Moreover, a design case of freezing chuck system is analyzed by COMSOL software to investigate the freezing/thawing functions and to evaluate its effectiveness.
查看更多>>摘要：Drop test is one of the common methods for determining the reliability of electronic products under actual transportation conditions. The aim of this study is to develop a reliable drop impact simulation technique. The test specimen of a printed circuit board is clamped at two edges on a test fixture and mounted on the drop test machine platform. The drop table is raised at the height of 50mm and dropped with free fall to impinge four half-spheres of Teflon. One accelerometer is mounted on the center of the specimen to measure the impact pulse. The commercial finite element software ANSYS/LS-DYNA is applied to compute the impact acceleration and dynamic strain on the test specimen during the drop impact. The finite element results are compared to the experimental measurement of acceleration with good correlation between simulation and drop testing. With the accurate simulation technique, one is capable of predicting the impact response and characterizing the failure mode prior to real reliability test.
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