Analytical solution for buckling of asymmetrically delaminated Reissner's elastic columns including transverse shear

The exact analytical solution of buckling in delaminated columns is presented. In order to investigate analytically the influence of axial and shear strains on buckling loads the geometrically exact beam theory is employed with no simplification of the governing equations. The critical forces are then obtained by the linearized stability theory. In the paper, we limit the studies to linear elastic columns with a single delamination, but with arbitrary longitudinal and vertical asymmetry of delamination and arbitrary boundary conditions. The studies of quantitative and qualitative influence of transverse shear are shown in detail and extensive results for buckling loads with respect to delamination length, thickness and longitudinal position are presented. (c) 2007 Elsevier Ltd. All rights reserved

Exact buckling analysis of composite elastic columns including multiple delamination and transverse shear

The exact analytical solution of buckling in beams with multiple delaminations is presented. In order to investigate analytically the influence of axial and shear strains on buckling loads, the geometrically exact beam theory is employed with no simplification of the governing equations. The critical forces are then obtained by the linearized stability theory. The parametric studies are designed so that they give us fundamental understanding of the effects of the delamination number, length and position on the buckling load. The effect of shear is found to be of substantial importance. (c) 2007 Elsevier Ltd. All rights reserved

Optimal Recovery of Elastic Properties for Anisotropic Materials through Ultrasonic Measurements

Full knowledge of material elastic properties is required to facilitate design in many applications. The existence of misorientation between the geometric axes of the part and the material symmetry axes has in particularly created challenged in design of composite structure. In this thesis the potential for optimal identification of material symmetries for a general anisotropic material through a water immersion technique is explored. The concept is extensible to any class of symmetry groups and does not assume a-priori knowledge of the material. Initial experimental results for determining the elastic constants as well as locating the symmetry planes are presented. Many materials have not been investigated completely by a method such as the one described. The specific contribution of this work is to demonstrate this process for experimental data sets. The primary focus is on carbon-carbon composite material. The method is demonstrated using a single crystal with known properties

The general theory of elastic stability at the end of the XIX century

This paper reviews the research on the theory of elastic stability published at the end of the 19th century, with emphasis on the work by G. H. Bryan in Cambridge. The state of the studies on structural stability previous to Bryan is reviewed, and two lines of work are identified: one is a general stability of rigid bodies and the other is a collection of case studies of elastic stability. Bryan's theory is discussed next, presenting his arguments based on first energy principles, which led him to strong conclusions. The importance of the word "general" and the idea of having solved the problem in each case are explained. The impact of the contributions made by Bryan, together with the critiques that this generated, is also discussed.Fil: Godoy, Luis Augusto. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentin

Control and structural optimization for maneuvering large spacecraft

Presented here are the results of an advanced control design as well as a discussion of the requirements for automating both the structures and control design efforts for maneuvering a large spacecraft. The advanced control application addresses a general three dimensional slewing problem, and is applied to a large geostationary platform. The platform consists of two flexible antennas attached to the ends of a flexible truss. The control strategy involves an open-loop rigid body control profile which is derived from a nonlinear optimal control problem and provides the main control effort. A perturbation feedback control reduces the response due to the flexibility of the structure. Results are shown which demonstrate the usefulness of the approach. Software issues are considered for developing an integrated structures and control design environment

Methods of applied dynamics

The monograph was prepared to give the practicing engineer a clear understanding of dynamics with special consideration given to the dynamic analysis of aerospace systems. It is conceived to be both a desk-top reference and a refresher for aerospace engineers in government and industry. It could also be used as a supplement to standard texts for in-house training courses on the subject. Beginning with the basic concepts of kinematics and dynamics, the discussion proceeds to treat the dynamics of a system of particles. Both classical and modern formulations of the Lagrange equations, including constraints, are discussed and applied to the dynamic modeling of aerospace structures using the modal synthesis technique

Planar, time-optimal, rest-to-rest slewing maneuvers of flexible spacecraft

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76605/1/AIAA-20370-687.pd

Determination of the Viscoelastic Properties of General Anisotropic Materials

Elastic properties are rarely sufficient in order to evaluate the condition of a composite material. Knowledge of the viscoelastic properties is very critical for design purposes, for they directly characterize damping. Damping related measurements in the material provides information about the degree of cross-linking and crystallinity of the polymer. For metals, damping may be related to dislocation motion among other characteristics. For composite materials, in general the interphase and the matrix dominate the damping of the material. Ultrasonic measurement of damping gives a non- destructive measure of strength of composite materials. This thesis considers damping characteristics of polymer matrix composites as well as reinforced carbon-carbon (RCC). These characteristics represent perhaps the best hope of developing a true index of state or damage tensor for composite materials. For polymer matrix composites the damping and elastic properties can be combined with either temperature or pressure to characterize the interatomic potentials in the matrix. This is the closest to a non- destructive measure of strength that is likely. By describing cross linkage and crystallinity this measure also provides insight into many of the most important degradation mechanisms. Part of this research looks into the recovery of stiffness tensor, material symmetry and principal axis. Damping is measured along this principal axis. It is also interesting to note that the damping is affected by oxidation, second part of this thesis looks into the oxidation effects of damping in RCC. Optimization routine is developed to solve Christoffel\u27s equation to recover the material stiffness tensor. Method to determine the initial guesses for the optimization routine is also developed in this thesis. An ultrasonic microscope with immersion transducers is used to extract data from samples. Oxidation is carried out in a tube furnace run at 700°C. Stiffness tensors for the samples are recovered from the measured data using a routine applying the solution to the Christoffel\u27s equation. Recovered stiffness tensors show satisfactory results. The orientation of the recovered stiffness tensors is very close to the material axis. Damping is measured with this variability. The variability in repeatability of damping measurements is less than 10%. Oxidation data obtained followed the initial assumptions and can be used for designing if damping accuracy can be improved

TWO-STAGE UTILITY MAXIMIZATION AND IMPORT DEMAND SYSTEMS REVISITED: LIMITATIONS AND AN ALTERNATIVE

Two-stage utility maximization theory has been widely used in the literature to estimate import demand for agricultural commodities that are often inputs. This article examines the overlooked conceptual and empirical limitations of applying two-stage utility maximization theory to model the demand for imported commodities that are inputs. A discussion is presented about how the underutilized theory of two-stage profit maximization overcomes these limitations. Also discussed are the conditions under which errors illustration of the two-stage profit maximization procedure is provided.Demand and Price Analysis, International Relations/Trade,

Integrated research in constitutive modelling at elevated temperatures, part 1

Topics covered include: numerical integration techniques; thermodynamics and internal state variables; experimental lab development; comparison of models at room temperature; comparison of models at elevated temperature; and integrated software development