Browsing by Subject "Strains and stresses"
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Item A failure prediction model for window glass(Texas Tech University, 1980-05) Beason, William L.There is a need within engineering practice for an analytical method to predict the probability of failure of window glass plates subjected to lateral loads. The failure prediction technique should include provision for all significant factors which influence glass strength and all significant factors which influence plate behavior The ultimate use of the glass plate failure prediction model will be to provide a realistic assessment of glass plate strength to be used in the design of window glass.Item A finite element complementary energy formulation for plane elastoplastic stress analysis(Texas Tech University, 1979-05) Azene, MulunehThe m.ethod of analysis presented herein parallels that of Ref (8) with two added major distingushing features. First, the present model consists of an eighteen degree of freedom self-equilibrating finite element model wherein the stress function is expressed by means of a complete set of quintic Hermitian polynomials. The function used, while allowing for selfequilibrating stresses that are continuous within the element, also enables the admission of all the second derivatives of the function as nodal parameters, thereby permitting the determination of nodal stress values directly without the need of additional computation. Second, the present work introduces an additional force parameter that is essential to satisfy complete static equilibrium of external forces constistent with the assumed stress function.Item A fuzzy sets based model of the interaction between stresses involved in manual lifting tasks(Texas Tech University, 1982-12) Karwowski, WaldemarThe primary objectives of this research were: 1. Development and testing of a mathematical, fuzzy sets based model for the acceptability of the stresses involved in lifting activity. 2. Evaluation of the hypothesis that a combination of the acceptability of the biomechanical and physiological stresses leads to an overall measure of lifting task acceptability, namely the acceptability of the psychophysical stress. 3. Development of a general criterion for establishing maximum permissible weights of load to be lifted safely. 4. Comparison and evaluation of existing recommendations versus this proposed general criterion. The group of acceptable weights of load that can be lifted safely was defined as a class with no sharp transition from membership to nonmembershlp. The acceptability measure of the stresses were associated with fuzziness, rather than randomness. Measures of acceptability were expressed by membership functions which describe the degree to which the stresses were acceptable for the human operator (with respect to the chosen design criteria). A synergistic effect was used as the basis to combine the biomechanical and physiological stresses into one category. The psychophysical methodology was used to carry out an experiment with nine male subjects to provide the data needed for the model development. An iterative procedure was used to generate conditions for membership functions which resulted in the minimum (or near-minimum) mean value of the Hamming distance between the acceptability measures of these stresses. The combined stress was then compared with the psychophysical one using the similarity measure between them. The conditions under which the acceptability of the psychophysical stress were similar to the acceptability of the combined stress were found. The points of reference for the biomechanical stress where the hypothesis holds true were also deterniined. A general criterion for the acceptability of the lifting task was proposed as one which considers the effect of both biomechanical and physiological stresses on the human operator's performance during manual lifting activities.Item A simplified model for analyzing the nonlinear dynamic response of thin plates(Texas Tech University, 1986-08) Lim, Gee LooNot availableItem A study of the differential deflections occurring in full-scale residential slab-on-ground foundations(Texas Tech University, 1985-08) Shih, Chaur-songNot availableItem Analysis of rectangular glass plates resting on flexible beams(Texas Tech University, 1988-05) Yu, Chia-juiNot availableItem Comparison of stresses of layered and monolithic glass plates(Texas Tech University, 1985-08) Nagalla, Sesha RNot availableItem The dynamic failure behavior of tungsten heavy alloys subjected to transverse loads(2004) Tarcza, Kenneth Robert; Taleff, Eric M.; Bless, Stephan J.Tungsten heavy alloys (WHA), a category of particulate composites used in defense applications as kinetic energy penetrators, have been studied for many years. Even so, their dynamic failure behavior is not fully understood and cannot be predicted by numerical models presently in use. In this experimental investigation, a comprehensive understanding of the high-rate transverse-loading fracture behavior of WHA has been developed. Dynamic fracture events spanning a range of strain rates and loading conditions were created via mechanical testing and used to determine the influence of surface condition and microstructure on damage initiation, accumulation, and sample failure under different loading conditions. Using standard scanning electron microscopy metallographic and fractographic techniques, sample surface condition is shown to be extremely influential to the manner in which WHA fails, causing a fundamental change from externally to internally nucleated failures as surface condition is improved. Surface condition is characterized using electron microscopy and surface profilometry. Fracture surface analysis is conducted using electron microscopy, and viii linear elastic fracture mechanics is used to understand the influence of surface condition, specifically initial flaw size, on sample failure behavior. Loading conditions leading to failure are deduced from numerical modeling and experimental observation. The results highlight parameters and considerations critical to the understanding of dynamic WHA fracture and the development of dynamic WHA failure models.Item Experimental study of edge displacements of laterally loaded window glass plates(Texas Tech University, 1979-05) Anians, Duncan CliveNot availableItem Finite element analysis of the behavior of nonlinear soil continua including dilatancy(Texas Tech University, 1975-12) Raghu, DorairajaTwo problems were analyzed in this research to study the behavior of soils subjected to loads. In the first problem, the behavior of both dense and loose sand was investigated, when a vertical steel plate is pushed into it. A new dilation finite element model based on variational principles was developed to study the effects of shear dilatancy in the sand. The second problem deals with a loaded footing resting on soft clay.Item Fracture and stress pattern correlations in glass plates(Texas Tech University, 1986-08) Wang, JuifengNot availableItem Geometrically nonlinear analysis of rectangular glass panels by the finite element method(Texas Tech University, 1980-05) al-Tayyib, Abdul-Hamid J.Not availableItem Nonlinear analysis of rectangular glass plates by finite difference method(Texas Tech University, 1981-08) Wang, Bob Yao-tingNot availableItem Nonlinear analysis of rectangular glass plates by Galerkin method(Texas Tech University, 1983-05) Ku, Fu-yuNot availableItem Nonlinear stress analysis of insulating glass units(Texas Tech University, 1986-05) Chou, Gee DavidNot availableItem Nonlinear thermoelastic stress analysis of spherically curved solar panels(Texas Tech University, 1985-05) Vungutur, Krishna V S RSpherically curved glass panels are used to concentrate solar energy onto a line focus in fixed mirror distributed focus type solar collectors. These solar panels consist of thin flat glass plates bent to form a spherical surface, glued onto a paper honeycomb backing, and covered with steel plate at the back and with plastic strips on the sides. Stresses are produced in the glass plates as they are formed into spherical surfaces. In addition, when the solar receiver is not in focus relative to the bowl and the sun, a mirror hot spot condition is developed, resulting in large thermally induced stresses within glass plates. The curved glass panel is modeled as a plate on elastic foundation in order to represent the behavior of the plate in relation to other panel components. Since lateral deflections of these plates are large compared to their thickness, nonlinear von Karman plate equations are used in the analysis, A computer model has been prepared to assist in the nonlinear analysis of stresses using finite difference method. The model has flexibility to analyze a variety of rectangular plate geometries subjected to thermal and other applied loads.Item Plastic buckling and collapse of circular cylinders under axial compression(2006) Bardi, Francois C.; Kyriakides, S.This study is concerned with the plastic buckling of relatively thick tubes and the ensuing succession of instabilities leading to their failure. The first instability is uniform axisymmetric wrinkling that is treated as a plastic bifurcation. As the wrinkles grow, the axial rigidity of the shell is gradually reduced. This eventually leads to a limit load instability beyond which failure in the form of localized deformation takes place. The problem is studied using experiments and analyses. Stainless steel specimens with D/t of 23-52 were custom-designed to avoid stress concentrations and reproduce long uniform pipe conditions. The specimens were compressed to failure under displacement control. In all cases, a second bifurcation involving nonaxisymmetric mode of deformation preceded the limit load. The bifurcation into axisymmetric wrinkling was determined by monitoring the development of wrinkles on the surface of the tubes. This critical state was successfully predicted using an anisotropic deformation theory of plasticity. The anisotropy of the material was established experimentally and modeled using Hill's quadratic anisotropic yield criterion. The problem was first modeled as uniform axisymmetric wrinkling. The model uses Sanders’ shell kinematics assuming small strains and moderately small rotations and includes a modified flow theory of plasticity to accommodate the anisotropy observed in the tubes. Small axisymmetric imperfections based on the critical halfwavelength were integrated into the model. The problem was formulated through the principle of virtual work and solved using Newton’s method. The solution correctly simulates the growth of wrinkles resulting in a limit load instability. The model included second bifurcation calculations from axisymmetric to non-axisymmetric configuration. Second bifurcation instabilities were found to occur before the limit load developed. For this reason, a second model was developed in which non-axisymmetric deformation of the shell was simulated by introducing both axisymmetric and nonaxisymmetric imperfections. Non-axisymmetric responses were found to be highly sensitive to the imperfections. Each experiment was first reproduced accurately by choosing the right combination of imperfections. However, to achieve a satisfactory prediction of the limit state over the whole range of D/t, a thorough parametric study of the imperfection sensitivity was performed. The relative amplitude of the axisymmetric imperfection to the non-axisymmetric imperfection was found to define whether the shell deforms axisymmetrically or not. Furthermore, if one of the imperfections governs the deformation configuration, then the effect of the second onto the response is negligible. Thus, a constant axisymmetric imperfection of 0.05% of the pipe wall thickness and a non-axisymmetric imperfection proportional to (D/t) 2 / m 3 yielded accurate predictions of both mode of deformation and limit load.Item Prediction of the dimensional instability resulting from machining of residually stressed components(Texas Tech University, 1995-08) Shin, Shang HyonResidual stresses, built into most manufactured components, are revealed most dramatically during subsequent machining operations. Depending on the magnitude and distribution of the original residual stress state, the remaining part of a machined component distorts in order lo maintain the equilibrium of internal forces, resultng in a new state of residual stress distribution in the remaining material. Given a known residual stress state in a material, the purpose of this research was to develop a methodology for the prediction of machining-induced distortions and the determination of the new state of residual stresses in the remaining material. In the first phase of this work, closed-form equations for the distortions of a residually stressed block, subjected to surface layer removal, were developed. Experimental and finite element simulations of the surface layer removal were also conducted and compared to the closed-form solutions. In the second phase of this study, analytical solutions for the distortions and residual stress re-distribution in a cylinder subjected to machining of the inner surface were developed. The original residual stress state was determined by the elasto-plastic solution of a cylinder subjected to the autofrettage process as well as the finite element simulations of the autofrettage process. The effect of isotropic as well as cylindrically orthotropic material properties on the ensuing machining distortions and the redistributions of residual stress state were studied. Closed-form solutions and finite element results of this study demonstrated excellent agreement in the determination of distortions and the new state of residual stresses due to material removal operations.Item Stress analysis of spherically curved rectangular and triangular solar panels(Texas Tech University, 1986-05) Lim, Kuang YakMany of the first mirror panels manufactured and installed on the 65-foot diameter FMDF test facility in Crosbyton, Texas have cracked glass surfaces. It is believed that the majority of the damage was caused by improper handling and the residual and thermal stresses in the panel. Since the cost of the solar panels is a considerable part of the total cost of the solar bowl, the analysis and design of these panels is crucial to the cost efficient design of the solar bowl. Various shapes of the solar panels are proposed to form the hemispherical solar bowl. Scaling-up of the reflector bowl from 65 feet to as much as 200 feet diameter is being considered by researchers. As such the main objective of this research is to develop a technique to analyze the residual stresses in the solar panels.Item The effect of the static fatigue constant upon window glass strength characterization(Texas Tech University, 1986-12) Hwang, Yuh-shingNot available