Transactions of the Canadian Society for Mechanical Engineering

Volume 30 (2006), Issue 3

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An approach for stabilising the finite element analysis of incompressible materials is presented. Although many effective methods exist for addressing incompressibility when applied forces or stress tractions are known, this paper explores cases where displacements are the only prescribed quantities on the boundary. In particular, the standard u-p formulation with isoparametric, quadrilateral, constant pressure, plane strain elements is considered. It is well known that these elements suffer from extreme numerical instability under displacement boundary conditions. A modified LU decomposition is used to filter the equations to produce a reduced nonsingular system leading to determination of the von Mises stress. The method is demonstrated with two test cases commonly used to assess element performance: a rectangular block in a uniform state of plane strain; and an axially restrained thick-walled cylinder subjected to internal and external pressures.

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Tungsten - Copper composites are generally used for electrical contact materials. These composites are suitable for hard working conditions such as intensive electrical sparks, gouging spark erosion, surface melting, welding, material transfer etc. The aim of the present article is to determine optimum processing conditions to improve the mechanical and physical properties of W-Cu composites with the view to increase their lifetime. W-Cu specimens are produced using powder material and the liquid infiltration process. Chemical composition, pressing machine pressure, infiltration time and temperature are variable parameters for specimen production. By optimizing the amount of cobalt addition, shaping pressure, time and temperature of production process, optimum values for mechanical and electrical properties such as density, hardness and resistivity are obtained.

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Dry machining is a very promising technology to reduce the machining cost and eliminate the negatives effects of lubricants on environment and on health. This technology is however difficult to apply for gummy materials which adhere to the cutting tools and for composites materials that wear out quickly the tools. In this research work, the effect of the cutting parameters, the alloys and that of hard particles (SiC, Al2O3) and soft particles (graphite) on the cutting forces and chip formation during dry machining is presented. The results obtained show that the machining laws relating the cutting conditions to the cutting force remain valid for the composites tested and for cutting speeds up to 150 m/min.

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The r-refinement increases accuracy of finite element solutions, but not increases computations. This paper presents a new and efficient technique applied to the r-refinement, which is based on the relative errors. This technique does not need a reference solution, and any physical quantity, such as energy, displacement, stress, etc., can be arbitrarily selected and applied to this technique. A simple algorithm is provided to find the optimum positions of nodes instead of solving a variety of nonlinear equations. Furthermore, this paper demonstrates this technique and provides a comprehensive finite element analysis of flexible axially moving beam by using the h-, p- and r-refinements.

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A commercial CFD code, CFX-TASCflow, is used to predict turbulent flow in a conical diffuser. The computation was performed using a low-Reynolds number k-ε model, low-Reynolds number k-ω model, a low-Reynolds number k-ω based non-linear algebraic Reynolds stress model, and a second moment closure with a wall-function. The experimental datasets of Singh [1] and Kassab [2] are used to validate the numerical results. The results show that all the turbulence models reproduce the static pressure coefficient distribution reasonably well. The low Reynolds number k-ω models give better prediction of the friction velocity than the second moment closure. The models also predict the Reynolds shear stress reasonably well but fail to reproduce the correct level of the kinetic energy.

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This paper describes an early fault detection strategy for a high performance hydrostatic actuation system, referred to as the ElectroHydraulic actuator (EHA). Safety is crucial for the EHA which is being applied in flight surface actuation systems and in robotics. The proposed fault detection methodology in this manuscript uses a new state/parameter estimation algorithm, referred to as the Unscented Kalman Filter (UKF) to estimate parameters which cannot be measured using sensors. The parameters reflect the health condition of the system and changes in their normal values can be related to the inception and progression of faults in the system. The two parameters of interest in this study are the viscous damping coefficient of a symmetrical actuator and the effective bulk modulus of the hydrostatic system. The feasibility of the approach is demonstrated by a simulation study and using experimental data. Changes in the viscous damping coefficient provide valuable information about the lubricating properties of the oil and the seal conditions of the actuator. Changes in the effective bulk modulus, as a result of air getting trapped in the system, will change the system response, affecting the natural frequency and may cause stability problems. In this paper, the UKF is used for the first time for parameter estimation in a hydraulic system.

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The aim of this paper is to develop a complete simulation model and study the tip-over responses of mobile cranes. The developed model takes into account all factors that could affect the overturning of truck cranes including: (i) detailed dynamics of the manipulator links and the base that can potentially rock back and forth, (ii) combined vehicle suspension and ground-tire compliance, (iii) condition of the ground under the wheels or the outrigger pontoons, (iv) friction between the outriggers/tires and the ground, (v) spatial motion of load carried, via a rope, by the telescopic boom of the truck crane, and (vi) hydraulic drive system. The model also includes the effect of the presence of the wheels that can support the machine in case of ground failure at any of the outrigger pontoons, and therefore is capable of predicting subsequent responses in case of soil failure under the crane supports. Simulation results are presented to understand tip-over responses of a typical mobile crane in the presence of load lifting, load swivel, ground failure and various ground conditions. The model developed in this paper is shown to be capable of producing detailed information about the machine responses, the reaction forces at crane' supports and the state parameters of drive system to various input scenarios. The acquired information could additionally be used for improving the design of the cranes in general.

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Precision injection molding technology can be applied for the computer, communication, electric appliance and medical components industries. This paper presents a new design of a tiebarless clamping system for micro-injection molding machine. The tiebarless clamping system can provide lots of convenience, such as more mold space for automation etc., for a micro-injection molding machine. Good parallel precision between stationary platen and movable platen of a clamping system is an important feature for high precision injection molding. With special mechanism of this tiebarless clamping system, the movable platen will deform with the stationary platen synchronously under high clamping force to maintain the parallelism. Via tests and verifications, the parallel precision is controlled at good condition under 6 tons of clamping force.

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Two numerical algorithms are presented here: the integration of the Poisson equation of attitude and the calculation of the angles from the elements of the matrix of attitude. The method here suggested lies in the use of a fast algorithm of Wilcox type in which the errors of commutation are eliminated by the use of a numerical artifice implemented in a data acquisition card: information on the angular velocity is given on only one channel among the three channels of the chart (the two other channels are put at zero) during a step of calculation. The numerical simulations are performed and validated by use of the Wilcox integration method which implies errors of commutation, with various orders of truncation, and by the integration method with an algorithm with two rates of calculation. By use of a strap-down inertial system and the Matlab software, real time experimental tests are carried out to calculate the best alternatives of the algorithm of integration resulted from the numerical simulations.

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This paper discusses the technology of undercutting on cam profiles to improve the transmission quality in cam-based speed-reducers. By means of the contact ratio and the pressure angle, two principles for undercutting are established to ensure a feasible mechanism. Polynomials are applied to generate the undercutting curves to satisfy our requirements. Finally, an example is given to illustrate the methodology.