Abstract: The Rapid Prototyping (R.P.) technology which is used in manufacturing a three-dimensional solid part is based on the layer forming method. Currently, the main streams of commercially available machines use the point or line forming method to create the solid part. A thin polymeric material layer is delivered by a roller or scraper to form a thin material layer for further layer forming. This process won’t be able to control the size of the forming part. In this paper, “Liquid Spray Process” is proposed to use a spray pen to spread a thin layer of polymeric material on the forming bed for further layer forming in a rapid prototyping system. It will decrease time and cost of the current R.P. machines by spreading proper size of thin forming bed. The setup of the system of the automatic spray pen, continuous material supply system, spray parameter settings and man-machine interface control system were discussed in this paper. Furthermore, the Taguchi Methods were applied to find the optimal spray forming parameters including height, velocity, acceleration, control air pressure, atomizing air pressure, fluid flow of spray, material pressure and speed of gear pump. Finally, the minimum uniform coating thickness could reach as low as 25 μm with “Liquid Spray Process” when the optimal parameters were used. The uniformity could be well maintained for both sprays in cross or in parallel directions to form an area of 120 mm × 150 mm with the optimal parameters.
Abstract: Two-phase heat transfer devices such as heat pipes and vapor chambers are composed of an evaporator, an adiabatic section and a condenser. For the dry-out prevention and capillary purpose, adiabatic sections and evaporators are covered by wick structures. Common wick structures are grooves, mesh, sintered powder and their combination. Combining with the wick structures, the major phase change effects on evaporators are thin-film evaporation. For the research between parameters of wick structure and evaporator performance, we developed a facility to measure the heat transfer on evaporators. To ensure the least heat losing, the path of heat flux and test condition were designed with several thermal guards. A pressure control system was established with balance mechanisms to maintain a stable condition of low pressure. Since temperature differences are very fast while the major phase change effect is thin-film evaporation, a high speed data acquisition system was used. Based on this test platform, the performance of evaporators can be determined at specific conditions.
Abstract: Failure modes of swept spot friction welds in lap-shear specimens of alclad 2024-T3 aluminum sheets are first investigated based on experimental observations. Optical and scanning electron micrographs of the welds before and after failure under quasi-static and cyclic loading conditions are examined. Experimental results show that the failure modes of the welds under quasi-static and cyclic loading conditions are quite different. Failure modes of swept spot friction welds depend considerably on the weld geometry, microstructure, and load amplitude. A fatigue crack growth model based on the paths of the dominant kinked fatigue cracks is developed to estimate the fatigue lives of the spot friction welds. The global and local stress intensity factors for finite kinked cracks, the stress intensity factors for finite transverse cracks, and the Paris law for fatigue crack propagation are used. The fatigue life estimations agree well with the experimental results.
Abstract: In this study, the microstructure and glass transition temperature (Tg) of five elements (Al-Cu-Cr-Fe-Ni) high-entropy alloy was evaluated under different Al content by molecular dyItalic textnamics (MD) simulations. The ensemble and COMPASS potential were used. Firstly, the Al-Cu-Cr-Fe-Ni high-entropy alloys were melted at high temperature and were cooled with a high quenching rate further. The radial distribution function (RDF),Wendt-Abraham parameter and X-ray diffractometer (XRD) were used to analyze the change on the microstructure and glass transition temperature (Tg) of Al-Cu-Cr-Fe-Ni high-entropy alloys. Simulation results show that the micro-structure of different aluminum content of AlxCuCrFeNi alloy after fast quenching are all amorphous state. When the aluminum content decreased, the amorphous state are more obvious and the glass transition temperature decreases.
Abstract: The performances characteristics of magnetic hydrodynamic tilted bearing with surface roughness lubricated with ferrofluid are studied in this study. To explore the effects of ferrofluid to the bearings, the Shah’s theoretical model and the modified items of characteristics related to magnetic ferrofluid are adopted. As the affections of surface roughness to the bearings, the stochastic Christensen Reynolds’ equation is applied; meanwhile, with the consideration of the non-zero mean α, variance σ and skewness ε. According to the results, comparing with the Newtonian fluids, the tilted bearing lubricated with magnetic ferrofluid has the higher built-up pressure distribution and load-carrying capacities. As the non-zero mean α of the surface roughness increases, the responding time decreases. On the other hand, increases the variation σ, decreases the responding time in longitudinal surface roughness; whereas, the transverse type has the inverse trend of responding time when variation increases.
Abstract: In the last decade, RFID (Radio Frequency Identification) technology has been applied in many applications to support the routine operations. These methods about RFID applications focus mainly on the specific issues in the application domains. In this study, a generic object relationship identification and guidance model is proposed to identify the relationships between objects (including human beings, physical goods and locations) and guide the objects toward their destination based on their predefined objectives via the RFID. Eight general types of object interactions including searching, blocking, no-in, no-out, conflict, intersection, coincidence, and support, are considered to identify object relationship and guide the objects. The proposed scheme consists of three modules namely object type combination (OTC), object relationship identification (ORI) and object guidance (OG). Moreover based on the proposed methodology, an Object Relationship Identification and Guidance System (ORIG-System) is developed and simulated environments are established in order to verify the feasibility and performance of the proposed model. As a whole, this study provides a methodology and system to provide effective support to the routine operations in distinct application domains via the RFID technology.
Abstract: Flywheels are kinetic energy storage and retrieval devices as chemical batteries. However, the high charge and discharge rates, as well as the high cycling capability make flywheels attractive as compared to other energy storage devices. This research serves as a preliminary study that aims for developing a technique in designing a flywheel rotor based on the solid isotropic method with penalization (SIMP) method. Examples are presented to illustrate the optimum structural layouts obtained given various design objectives. For a static rotor, the objectives are maximizing the first torsional natural frequency, maximizing the moment of inertia and maximizing both of them, respectively. The problem is formulated using bound formulation and the method of moving asymptotes (MMA), a first-order optimization technique, was employed. Therefore the design sensitivity becomes a necessity. The so-called checkerboard problem in the topology optimization is avoided using the nodal design variable. Also, a threshold is used to reduce the numerical imperfection in each iteration. For the topology design of a rotating rotor, the centrifugal force induced in the high-speed rotation is considered. The objective is to maximize the rotor stiffness and is demonstrated in the last example. Results show clear topology layout of flywheel was obtained using proposed method.
Abstract: For three-dimensional (3-D) mapping, so far, 3-D laser scanners and stereo camera systems are used widely due to their high measurement range and accuracy. For stereo camera systems, establishing corresponding point pairs between two images is one crucial step for reconstructing depth information. However, mapping approaches using laser scanners are still restricted by a serious constraint by accurate image registration and mapping. In recent years, time-of-flight (ToF) cameras have been used for mapping tasks in providing high frame rates while preserving a compact size, but lack in measurement precision and robustness. To address the current technological bottleneck, this article presents a 3-D mapping method which employs an RGB-D camera for 3-D data acquisition and then applies the RGB-D features alignment (RGBD-FA) for data registration. Experimental results show the feasibility and robustness of applying the proposed approach for real-time 3-D mapping for large-scale indoor environments.
Abstract: Micro metal forming is widely interested due to its potential in manufacturing micro parts with low costs and high production rate as the demands of compact devices have been increasing in many fields. This study uses micro ball punch deformation tests to investigate the effect of grain size on the formability of SUS 304 stainless steel sheets. The study employed annealing treatments to change the grain size of the sheets. By using three punches in different diameters in associated with three dies having an inner diameter of 2 mm and different die radii, it was able to perform micro bulging tests and obtain the bulging depths which were used to assess the formability of the sheets. The study shows that the grain size does affect the depth of the deformed dome in the ball punch deformation test at the micro scale.
Abstract: A three-dimensional atomic-scale finite element model was developed in this paper for simulation of a nano-scale uniaxial tension. First, the Morse’s potential function was used to simulate the forces acting among particles. Furthermore, a non-linear spring and dashpot element with a lumped mass was used to establish an atomic model. The elongation of the spring at fracture was used to simulate the radius of fracture of the atomic link. This method was applied to investigate the proportional tension test of an idealized FCC single crystal copper film along the x direction. The study includes the stress-strain curve, the effect of five categories of atomic distances on the stress-strain curve; and the effect of strain-rate on the stress-strain curve. The results showed that (1)the simulated maximum stress for copper is very close to 30.0GPa, which is also the value of maximum equivalent stress obtained by Lin and Hwang , verifying the validity of the calculation of this paper. In the tension test of copper, necking develops gradually and eventually leads to fracture. The simulated deformed material element during each stage of deformation was similar to that simulated by Komanduri et al.(2)the influence of =6.2608 on the five categories of atomic distance considered was limited and it may be neglected to save computation time,(3)when the strain-rate was large, the resistance to deformation was also large, leading to an increase in the yield stress and fracture stress.