Labor and management are considered basic elements in cyclic conflict. A model is developed assuming that their interactions arise solely from the sustenance needs of the elements. The “size”; and “state”; determining the condition of the... more
Labor and management are considered basic elements in cyclic conflict. A model is developed assuming that their interactions arise solely from the sustenance needs of the elements. The “size”; and “state”; determining the condition of the elements are defined. Analysis of the interactive industrial forces yield the governing differential equations of the industrial system. The industrial system is assumed to
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This paper contains a thermodynamic analysis of electron emission from a micro-fabricated diamond tip array. The analysis is based on experimental measurements of the current-voltage characteristics of an actual device. Field enhancement,... more
This paper contains a thermodynamic analysis of electron emission from a micro-fabricated diamond tip array. The analysis is based on experimental measurements of the current-voltage characteristics of an actual device. Field enhancement, applied field, and electrical current density are shown to influence thermodynamic performance. The idealized thermodynamic analysis predicts cooling rates above 10 W/cm2 for an existing device under room
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Purpose The purpose of this paper is to evaluate the tool experiences using torque during welding as a means of in-process sensing for tool wear. Metal matrix composites (MMCs) are materials with immense potential for aerospace structural... more
Purpose The purpose of this paper is to evaluate the tool experiences using torque during welding as a means of in-process sensing for tool wear. Metal matrix composites (MMCs) are materials with immense potential for aerospace structural applications. The major barrier to implementation of these materials is manufacturability, specifically joining MMCs to themselves or other materials using fusion welding. Friction stir welding (FSW) is an excellent candidate process for joining MMCs, as it occurs below the melting point of the material, thus precluding the formation of degradative intermetallics’ phases present in fusion welded joints. The limiting factor for use of FSW in this application is wear of the tool. The abrasive particles which give MMCs their enhanced properties progressively erode the tool features that facilitate vertical mixing and consolidation of material during welding, resulting in joints with porosity. While wear can be mitigated by careful selection of process parameters and/or the use of harder tool materials, these approaches have significant complexities and limitations. Design/methodology/approach This study evaluates using the torque the tool experiences during welding as a means of in-process sensing for tool wear. Process signals were collected during linear FSW of Al 359/SiC/20p and correlated with wear of the tool probe. The results of these experiments demonstrate that there is a correlation between torque and wear, and the torque process signal can potentially be exploited to monitor and control tool wear during welding. Findings Radial deterioration of the probe during joining of MMCs by FSW corresponds to a decrease in the torque experienced by the tool. Experimentally observed relationship between torque and wear opens the door to the development of in-process sensing, as the decay in the torque signal can be correlated to the amount of volume lost by the probe. The decay function for tool wear in FSW of a particular MMC can be determined experimentally using the methodology presented here. The decay of the torque signal as the tool loses volume presents a potential method for control of the wear process. Originality/value This work has near-term commercial applications, as a means of monitoring and controlling wear in process could serve to grow commercial use of MMCs and expand the design space for these materials beyond net or near-net-shape parts.
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Point defect formation associated with early stages of optical damage was observed unexpectedly in two, and possibly three, different optical materials subjected to short-duration space exposure. Three calcium fluoride, two lithium... more
Point defect formation associated with early stages of optical damage was observed unexpectedly in two, and possibly three, different optical materials subjected to short-duration space exposure. Three calcium fluoride, two lithium fluoride, and three magnesium fluoride samples were flown on Space Shuttle flight STS-46 as part of the Evaluation of Oxygen Interactions with Materials - Third Phase experiment. One each of the calcium and magnesium fluoride samples was held at a fixed temperature of 60 C during the space exposure, while the temperatures of the other samples were allowed to vary with the ambient temperature of the shuttle cargo bay. Pre-flight and post-flight optical absorption measurements were performed on all of the samples. With the possible exception of the magnesium fluoride samples, every sample clearly showed the formation of F-centers in that section of the sample that was exposed to the low earth orbit environment. Solar vacuum ultraviolet radiation is the most probable primary cause of the defect formation; however, the resulting surface metallization may be synergistically altered by the atomic oxygen environment.
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Many authors have described ways of calculating the efficiency of thermoelectric devices. These calculations usually make simplifying assumptions to define the behavior of the device. The most common of these is to make the thermoelectric... more
Many authors have described ways of calculating the efficiency of thermoelectric devices. These calculations usually make simplifying assumptions to define the behavior of the device. The most common of these is to make the thermoelectric material properties constant. This paper presents work in progress toward simulating the behavior of real thermoelectric devices. We present the steady state differential equations defining the behavior of thermoelectric materials and the associated boundary conditions required to solve power generation and cooling element problems. We implemented a simple one-dimensional simulation of a power-generating device using B-spline collocation methods. The results of the simulation are compared to an example presented by Angrist (1976).
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A friction stir system for processing at least a first workpiece includes a spindle actuator coupled to a rotary tool comprising a rotating member for contacting and processing the first workpiece. A detection system is provided for... more
A friction stir system for processing at least a first workpiece includes a spindle actuator coupled to a rotary tool comprising a rotating member for contacting and processing the first workpiece. A detection system is provided for obtaining information related to a lateral alignment of the rotating member. The detection system comprises at least one sensor for measuring a force experienced by the rotary tool or a parameter related to the force experienced by the rotary tool during processing, wherein the sensor provides sensor signals. A signal processing system is coupled to receive and analyze the sensor signals and determine a lateral alignment of the rotating member relative to a selected lateral position, a selected path, or a direction to decrease a lateral distance relative to the selected lateral position or selected path. In one embodiment, the friction stir system can be embodied as a closed loop tracking system, such as a robot-based tracked friction stir welding (FSW) or friction stir processing (FSP) system.
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... Auteur(s) / Author(s). COOK George E. (1) ; SMARTT Herschel B. (2) ; MITCHELL Jason E. (3) ; STRAUSS Alvin M. (4) ; CRAWFORD Reginald (4) ; ... Localisation / Location. INIST-CNRS, Cote INIST : 6039, 35400011831931.0010. Nº notice... more
... Auteur(s) / Author(s). COOK George E. (1) ; SMARTT Herschel B. (2) ; MITCHELL Jason E. (3) ; STRAUSS Alvin M. (4) ; CRAWFORD Reginald (4) ; ... Localisation / Location. INIST-CNRS, Cote INIST : 6039, 35400011831931.0010. Nº notice refdoc (ud4) : 14851609. ...
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ABSTRACT
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Abstract Temperature measurements of the weld during friction stir welding (FSW) have previously been carried out using various methods including infra-red imaging/thermometers, embedded thermocouples in the parent metal as well as direct... more
Abstract Temperature measurements of the weld during friction stir welding (FSW) have previously been carried out using various methods including infra-red imaging/thermometers, embedded thermocouples in the parent metal as well as direct ...
ABSTRACT Two variational techniques with wide application to various heat transfer problems are described. The first is the chain system method applicable to th
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Research Interests: Computational Modeling, Packaging, Modeling and Simulation, Path planning, Parallel Robots, and 14 moreInteroperability, Kinematics, Robot kinematics, Graphic User Interface Design, Computer Languages, Collision detection, Inverse Kinematics, Graphical User Interfaces, Open Systems, Computer Graphic, Mathematical Model, Path Planning, Programming language, and Matrix transformation
This paper reviews the biomedical literature concerning human adaptation to nonterrestrial environments, and focuses on the definition of practical countermeasures necessary for long-term survival on the Moon, Mars and during long-term... more
This paper reviews the biomedical literature concerning human adaptation to nonterrestrial environments, and focuses on the definition of practical countermeasures necessary for long-term survival on the Moon, Mars and during long-term space missions and exploration. Of particular importance is the development of clinically relevant countermeasures for prevention of pathophysiological changes in the musculoskeletal and cardiopulmonary systems under these conditions. The countermeasures which are proposed are based upon a combination of biomechanical and theoretical analyses. The biomechanical analyses are based upon clinical measurements of human skeletal density changes associated with weight lifting as well as clinical studies of human strength and fitness currently being conducted using an isoinertial trunk dynamometer. The theoretical analysis stems from a mathematical model for bone loss in altered gravity environments that we have begun to develop. These analyses provide guide...
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ABSTRACT
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In using the finite element method to examine certain aspects of the mechanical behavior of the human lumbar spine, most investigators have made numerous simplifying assumptions regarding the geometric and material data used to build a... more
In using the finite element method to examine certain aspects of the mechanical behavior of the human lumbar spine, most investigators have made numerous simplifying assumptions regarding the geometric and material data used to build a model of the spine. Since there are no specific rules for choosing geometric and material data for a "normal" human lumbar spine, considerably different types of models have been used by investigators in their finite element studies. In this study, variations in model geometric and material properties are shown to significantly affect the finite element results of an axisymmetric model of the human lumbar spine under axial compression. The Young's moduli of the cancellous bone and intervertebral disc annulus, Poisson's ratios of the cartilaginous end-plate and disc annulus, the width of the disc annulus, the height of the disc, and the ratio of the disc nucleus pressure and axial pressure are recognized as the parametric variables that most significantly affect the finite element solution.
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ABSTRACT
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ABSTRACT
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A three-dimensional computational fluid dynamic (CFD) model is used to simulate the control of the temperature of a friction stir welding (FSW) tool during the joining process. The CFD software package FLUENT was used to create the... more
A three-dimensional computational fluid dynamic (CFD) model is used to simulate the control of the temperature of a friction stir welding (FSW) tool during the joining process. The CFD software package FLUENT was used to create the numerical model. The simulation was executed in a small cluster computing environment to improve the runtimes of the model. Within the model the FSW tool was elevated and maintained at a temperature higher than temperatures experienced during the FSW process. This paper examines the axial force associated with the FSW process when the tool is maintained at an elevated temperature. The FSW tool temperature in the model was optimized to reduce the axial force experienced by the tool during joining. Using the CFD model along with the DAKOTA software package from Sandia National Labs an optimal elevated tool temperature was found that reduced the axial load experienced by the FSW tool by 25%.
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As friction stir welding (FSW) has expanded to welding higher strength materials, large process forces and extreme tool wear have become issues. One possible solution is introducing an additional heating source in front of the FSW tool... more
As friction stir welding (FSW) has expanded to welding higher strength materials, large process forces and extreme tool wear have become issues. One possible solution is introducing an additional heating source in front of the FSW tool which softens the material and reduces the tool loads. We investigate the advantages of elevating temperature. Bead on plate welds were performed with
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This paper examines the dynamic behaviors of inflated beam aerospace structures. The principal foci of this investigation are the determination of the damping mechanisms active in structures constructed from inflated cylindrical beams,... more
This paper examines the dynamic behaviors of inflated beam aerospace structures. The principal foci of this investigation are the determination of the damping mechanisms active in structures constructed from inflated cylindrical beams, development of a practical modeling method ...
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This paper evaluates the factors that control the flexibility of fabric space-suit elements, in particular gloves, by examining a bending model of a pressurized fabric tube. Results from the model are used to evaluate the design... more
This paper evaluates the factors that control the flexibility of fabric space-suit elements, in particular gloves, by examining a bending model of a pressurized fabric tube. Results from the model are used to evaluate the design strategies used in space-suit components, to evaluate the current direction in research on highly mobile space-suit gloves and to suggest changes necessary for optimum glove fabric selection. Finally it is shown that the modulus of the fabric used in space-suit joint construction is as important to the flexibility of the joint as the glove size and design.
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Noether's theorem and Noether's inverse theorem for generalised mechanical systems described by Lagrangian functions of the second order and non-conservative forces are established. The existence of the first integral... more
Noether's theorem and Noether's inverse theorem for generalised mechanical systems described by Lagrangian functions of the second order and non-conservative forces are established. The existence of the first integral depends on the existence of solutions of the generalised Noether-Bessel-Hagen equation. The theory is based on the idea that the transformations of time and generalised coordinates together with non-conservative forces determine
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Friction stir welding (FSW) joins materials by plunging a rotating tool into the work piece. The tool consists of a shoulder and a pin that plastically deforms the parent materials and then forges them together under the applied pressure.... more
Friction stir welding (FSW) joins materials by plunging a rotating tool into the work piece. The tool consists of a shoulder and a pin that plastically deforms the parent materials and then forges them together under the applied pressure. To create the pressure needed for forging, a rather large axial force must be maintained on the tool. Maintaining this axial force is challenging for robots due to their limited load capacity and compliant nature. To address this problem, force control has been used, and historically, the force has been controlled by adjusting the plunge depth of the tool into the work piece. This paper develops the use of tool traverse speed as the controlling variable instead of plunge depth. To perform this investigation, a FSW force controller was designed and implemented on a retrofitted Milwaukee Model K milling machine. The closed loop proportional, integral plus derivative (PID) control architecture was tuned using the Ziegler–Nichols method. Results show t...