• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 722
  • 290
  • 290
  • 290
  • 290
  • 290
  • 288
  • 121
  • 89
  • 10
  • 9
  • 2
  • Tagged with
  • 1355
  • 1355
  • 674
  • 546
  • 545
  • 350
  • 184
  • 156
  • 94
  • 76
  • 73
  • 72
  • 72
  • 67
  • 56
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
181

Moment-rotation characteristics of semi-rigid high tensile bolted connections-III.

Leon, Emmanuel. V. January 1961 (has links)
In riveted beam to column web connections the relationship between the connection‘s end rotation and moment have received considerable attention in the past. Numerous tests and studies have been made using various combinations of beams, connections and column sizes. However, little is known about the relationship of moment and rotation in high-tensile bolted beam to column connections.
182

Design and fabrication of a lightweight robotic manipulator

Roy, Matthew MacGregor. January 1997 (has links)
Typically, when a robotic manipulator undergoes rapid acceleration, there is a commensurate loss in end-effector positional accuracy. To achieve high accuracy of the working end, massive links are usually required. Conversely, to achieve high accelerations, thin and flimsy links have to be employed, only to be plagued by large end-effector vibrations and long settling times. However, this traditional tradeoff can be circumvented through the application of high-performance materials such as graphite/epoxy which exhibits high stiffness-to-weight and strength-to-weight ratios as well as good damping properties. This thesis describes the process of designing and fabricating the three principal mechanisms of an anthropomorphic lightweight robotic arm: the shoulder joint, elbow joint and wrist. Each mechanism comprises various components which were individually optimized for strength stiffness and weight by finite element analysis. The components were then synthesized into shoulder, elbow and wrist mechanisms that exhibited excellent workspace, low backlash and low friction. This lightweight composite manipulator was developed as a multi-purpose arm for possible applications in the remote repair of hydroelectric power lines, minesweeping and the handling of hazardous materials.
183

A combined approach for analysis of single crystal nickel base superalloys /

Bande, Gilbert. January 2001 (has links)
The purpose of this research is to develop a new tool for mechanical design and analysis of single crystal (SC) nickel base superalloys used in gas turbine engine components. The principle of this tool is based on the extension of the predictive models for isotropic material behavior to anisotropic materials such as SC nickel, base superalloys. This objective is achieved by combining the two main approaches used in the literature for SC materials development: the macroscopic approach and the microscopic approach. For that reason, this theory is designated as the "combined approach " (CA). / The structure of the CA theory requires two main elements: a viscoplastic model (that admits a yield function) and a slip factor. The viscoplastic model describes the behavior of the material in the macroscopic level. Conversely, the slip factor based on the crystallographic theory, accounts for the micro-slip state that dominates SC materials during deformation. / In order to determine the slip factor, a preliminary slip trace study of the crystal is established. Also to determine material constants from experimental data, a procedure has been developed to reduce the 3D basic equations into a one-dimensional form. The model has been evaluated for its predictive capability on SC material behavior including orientation dependence of the initial yielding, tension/compression asymmetry, stress-strain response, fully reversed cyclic response, creep response and relaxation response. In almost all the cases, good correlation has been observed between the predicted responses and experimental data, when available. Furthermore, it is believable that the CA can be successfully used for many other SC materials such as the body-centered-cubic (b.c.c) or the hexagonal-closed-packet (h.c.p). In view of all these results, the CA theory seems to offer the greatest promise in this regard. Limitations and future development needs are discussed.
184

Direct simulation Monte Carlo model of a couette flow of granular materials

Basik, Beata-Marie January 1990 (has links)
Since life-threatening natural phenomena, such as, snow avalanches and lava flows, and many industrial and agricultural material handling processes may be classified as granular flows, establishing constitutive relationships which model granular flow behaviour is of prime importance. While laboratory experiments attempting to support granular flow theory have been plagued by poor instrumentation, numerical simulations are becoming increasingly helpful in understanding the nature of these flows. The present investigation describes such a simulation developed within the framework of the Direct Simulation Monte Carlo model for rarefied gases presented in Bird (1976) and granular flow kinetic theory according to Lun, et al. (1984). More specifically, the model generates a Couette flow of smooth, inelastic, homogeneous, spherical granular particles. Two different boundary condition models are used to model the flow field's upper and lower boundaries: the Periodic Boundary Condition (PBC) model and the Finite Shear Layer (FSL) model. An essentially uniform shear flow with virtually no slip at the boundaries results from both boundary conditions. Stress and granular temperature results obtained with the PBC and FSL models for the lower range of solids fractions ($ nu < 0.3)$ compare very well with the Lun, et al. (1984) theory. At higher solids fractions, while the total stresses generated with both boundary models are in reasonable agreement with the latter theory and results from other numerical work, higher than expected streaming stresses appear to be compensating for lower than expected collisional stresses; as a result, granular temperature in this range of solids fractions proves to be higher than predicted.
185

Skating mechanics of change of direction maneuvers in hockey players

Fortier, Antoine January 2011 (has links)
Ice hockey is a popular winter sport that involves many skating skills improved by coaching instruction and numerous hours of practice. Once the basic mechanics of skating have been honed, the open game context requires rapid skating transitions between skating skills so as to effectively navigate about the ice surface to evade opponents and move in strategic tandem with teammates. Consequently, a player's performance relates in large part to effective change of direction maneuvers. The purpose of this study was to observe the kinetics of change of direction maneuvers in hockey players while wearing one of two skate models: a conventional skate and a skate with enhanced ankle mobility. Eight subjects with competitive ice hockey playing experience performed 90º change of direction tasks both to their left and then right sides for both skate models. Kinetic data were collected using a portable acquisition device connected to force strain gauge transducers on the blade holder. During a change of direction maneuver, a significant difference in the force applied by the inside and outside skates was noted (p < 0.05). No significant differences were observed as a main effect for skate model and turn direction. Significant differences were noted when leg side (inside/outside) was compared with skate model or turn direction (p< 0.05). This can provide insight to ice hockey coaches for training and skill development purposes but also to ice hockey skate manufacturers for future directions related to injury prevention and skating performance. / Étant un sport d'hiver populaire, l'hockey sur glace englobe plusieurs tâches de patinage qui sont améliorées par l'enseignement des entraîneurs accompagné de plusieurs heures de pratique. Une fois que les bases du patinage sont maîtrisées, le contexte du jeu ouvert requière des habilitées de transition rapide à travers les aptitudes de patinage pour naviguer effectivement sur la surface glacée afin d'évader les adversaires et se déplacer de manière stratégique avec les coéquipiers. Par conséquence, la performance d'un joueur est largement reliée aux mouvements de changement de direction. L'objectif de cette étude est d'observer la kinétique des mouvements de changement de direction de joueurs d'hockey en portant soit un patin conventionnel ou un patin avec une plus grande mobilité à la cheville. Huit sujets avec de l'expérience compétitive d'hockey on performés des mouvements de changement de direction de 90º à gauche et a droite pour les deux type de patins utilises. Des données kinétiques on été collectées en utilisant un système portable d'acquisition de données connecté à des jauges de déformation situés entre la lame et la botte du patin. Durant un mouvement de changement de direction, une différence significative a été observée au niveau de la distribution du poids entre la jambe extérieure et intérieure (p > 0.05). Aucune différence significative n'a été notée pour les deux modèles de patin ou par rapport à la direction du virage. Des différences significatives ont été observées lorsque la jambe intérieure ou extérieure a été comparée avec le type de patin utilisé ou la direction du virage (p > 0.05). Ceci nous donne de l'information par rapport aux stratégies d'entrainement des joueurs d'hockey ainsi que pour la fabrication de futurs modèles de patin pour la performance et la prévention aux blessures.
186

Oblique impact on sand.

Townsend, David. L. January 1953 (has links)
By the very nature of its subject, soil mechanics as compared to a modern science is inexact. Of necessity, idealized sections have been assumed in the determination of the various theories which govern the action of a soil. However, in the field all the local vagaries of nature come into play and the resulting heterogeneous mass is difficult to analyse and inconsistent in its properties. Thus, the field or soil mechanics has seen two parallel paths utilized in its development. The theoretical path has led to a fuller understanding of the stresses and strains which affect the soil; but the rigorous application of these theories has not proved completely satisfactory in the field.
187

Intergranular water and permeability of the Lake Vostok accretion ice, Eastern Antarctica

Jepsen, Steven Michael. Unknown Date (has links)
Thesis (Ph. D.)--Montana State University, 2005. / (UnM)AAI3187809. Source: Dissertation Abstracts International, Volume: 66-08, Section: B, page: 4311. Adviser: Edward E. Adams.
188

Interface-tracking by the face-offsetting method for martensitic transformation simulations /

Bellur Ramaswamy, Ravi S. January 2007 (has links)
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1273. Adviser: Daniel A. Tortorelli. Includes bibliographical references (leaves 84-86) Available on microfilm from Pro Quest Information and Learning.
189

Failure of microelectromechanical systems under dynamic loading : an experimental and numerical investigation /

Kimberley, Jamie, January 2008 (has links)
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-05, Section: B, page: 3078. Adviser: John Lambros. Includes bibliographical references (leaves 163-168) Available on microfilm from Pro Quest Information and Learning.
190

A new node-to-node approach to contact/impact problems for two dimensional elastic solids subject to finite deformation /

Xu, Daqing, January 2008 (has links)
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-05, Section: B, page: 3165. Adviser: Keith D. Hjelmstad. Includes bibliographical references (leaves 121-126) Available on microfilm from Pro Quest Information and Learning.

Page generated in 0.0742 seconds