Applied Mechanics and Materials Vols. 110-116

Abstract: It is found that springback is also sensitive to a range of material parameters, such as plastic anisotropy, evolution of elastic properties, yielding function and the Bauschinger effect particularly for loading/unloading operations. In this research, the effects of significant parameters on springback in U-die bending of CK67 anisotropic steel sheet are studied by numerical simulation and experiment. The results would compare springback of the die and eventually propose.

Abstract: Large deformation is a major deformation operation in many metal-forming processes, such as forging, rolling, extrusion, stamping and fine-blanking. It is difficult to study the deformation changes in these processes in a practical way, through the measurement of forces, due to the severe and localized nature of plastic deformation such as in the fine-blanking operation. Therefore, the forces analysis of most metal-forming processes cannot be carried out successfully by experiments. Thus, this paper aims to present the development of an effective process of forces measurement in fine-blanking process. Also, the effect of blank geometry and material properties on forming force in fine-blanking process was studied by theoretical formulation and experimental approach. Tensile strength and initial blank thickness were considered in this research. The obtained results indicated that by increasing the initial blank thickness and the tensile strength, the forces in fine-blanking process is increased.

Abstract: Crab walking is the most general and very important one for omni-directional walking of a hexapod robot. This paper presents a dynamic model for determining energy consumption and energy efficiency of a hexapod robot during its locomotion over flat terrain with a constant crab angle. The model has been derived for statically stable crab-wave gaits by considering a minimization of dissipating energy for optimal foot force distribution. Two approaches, such as minimization of norm of feet forces and minimization of norm of joint torques have been developed. The variations of average power consumption and energy consumption per weight per traveled length with velocity or stroke have been compared for crab walking with tripod and tetrapod gait patterns. Tetrapod gaits are found to be more energy-efficient compared to the tripod gaits.

Abstract: Real-time simulation of deformable solids is essential for some applications such as biological organ simulations for surgical simulators. In this work, deformable solids are approximated to be linear elastic, and an easy and straight forward numerical technique, the Finite Point Method (FPM), is used to model three dimensional linear elastostatics. Graphics Processing Unit (GPU) is used to accelerate computations. Results show that the Finite Point Method, together with GPU, can compute three dimensional linear elastostatic responses of solids at rates suitable for real-time graphics, for solids represented by reasonable number of points.

Abstract: Polymer Electrolyte Membrane (PEM) fuel cells are clean electrical power generators for applications normally up to 100 kW power requirements. It has the advantage of fast start-up due to its low operating temperatures of 60oC to 100oC. However, the low temperature requirement has to be addressed with an efficient thermal management system. For an air-cooled PEM fuel cell, cooling channels with a straight rectangular configuration are widely applied. This work establishes a computational methodology for the analysis of coolant flow mechanics related to the channel geometry for a specific bipolar plate size. The velocity and thermal gradient, average velocity rise factor (AVRF) and total cooling rates were determined from Computational Fluid Dynamics simulation based on initial coolant Reynolds number of approximately 250 to 750 with a steady heat flow of 82W. All geometries showed nearly 100% cooling capability respective to the heat load, but differ in the aspects of average plate temperature achieved, its temperature profile as well as existing gradient. From the analytical perspective of thermo fluids engineering, the selection criteria of suitable micro cooling channel configurations, depending on operating priority, was established.

Abstract: Cavitation, usually known as a destructive phenomenon, involves turbulent unsteady two-phase flow. Having such features, cavitating flows have been turned to a challenging topic in numerical studies and many researches are being done for better understanding of bubbly flows and proposing solutions to reduce its consequent destructive effects. Aeration may be regarded as an effective protection against cavitation erosion in many hydraulic structures, like gated tunnels. The paper concerns numerical simulation of flow in discharge gated tunnel of a dam using RNG model coupled with the volume of fluid (VOF) method and the zone which is susceptible of cavitation inception in the tunnel is predicted. Then a vent is considered in the mentioned zone for aeration and the numerical simulation is done again to study the effects of aeration. The results show that aeration is an impressively useful method to exclude cavitation in mentioned tunnels.

Abstract: This research presents a running model for a compliant wheel-leg hybrid mobile robot. A wheel-leg consists of three legs arranged by 120 degrees to each other and passive compliant joints. For simplicity, each leg is treated as a linear spring such that a traditional mass-spring model can be applied to model running of the wheel-leg hybrid robot. In order to achieve stable running, we propose a simple controller that can converge a robot leg to a desired angle of attack asymptotically during the swing phase. Hybrid wheel-leg running is then simulated and results are discussed.

Abstract: Freeze concentration is a process in which water is selectively separated out of binary solution in the form of ice, thereby concentrating solution. The freeze concentration system under consideration is a heat pump based freeze concentration system (FCS) that uses layer freezing process. The application of this system for the present paper is in the process of jaggery making used to concentrate sugarcane juice. A mathematical model is developed that helps in simulation of system under various operating parameters. The model is validated using previously published experimental results. Finally, based on simulation effects of various system parameters on ice growth and subsequent juice concentration have been discussed.

Abstract: This paper deals with a system with elements with one element is the main element and the other elements are the spare parts of the main element. If one element fails, one of the spare parts starts working immediately. The failure rate of non working elements are zero and the failure rate of working element is time dependent as and the failed elements are not repairable. The system works until all elements failed. In the second part of this paper the differential equations between the state of the system are established and by solving this equation the reliability function of the system () is calculated. In the third part, a numerical example solved to determine the parameters of the system. Nomenclature The notations used in this paper are as follows: : Number of elements, : Failure rate of each element at time, : Probability that the system is in state with spare element at time, : Probability that system works at time, : Mean time to failure of the system,

Abstract: Thermal energy generated by the friction between the disc and pad is transferred to both components and causes thermal expansion of material of each component, and futher affects the friction contact condition. This is the main factor of the thermoelastic instability (TEI) of a disc brake. In this study, TEI is analyzed using the finite element analysis technique. Three dimensional thermo-mechanical analysis model of the disc brake system is created. An intermediate processor based on the staggered approach is used to exchange analysis results: temperature, friction contact power, nodal displacement and deformation. Disc thickness variation (DTV) and temperature distribution of the disc are calculated, and the tendency and meaning of the results are discussed.