Study of Mixed Mode stress intensity factors by two- and three-dimensional photoelasticity

An experimental study was performed to investigate the stress intensity factors from two-dimensional inclined edge cracked models and three-dimensional inclined semi-circular surface cracks that penetrate part-way through a thick plate;To improve the accuracy of photoelastic data collection, fringe multiplication and fringe sharpening technique with a digital image processing system were used. Fracture coefficients, together with the exact origin of the crack tip, were extracted from data sets that produced an overdeterministic system of equations solved by an iterative least squares method. Power series type Williams equations were used in the analysis. The accuracy of the experimental results were evaluated qualitatively and quantitatively. For qualitative visual assessment, regenerated fringes were plotted by using the fracture equations and coefficients estimated from the data sets. For quantitative accuracy evaluation, statistical parameters, such as standard deviation and correlation coefficients between theoretical and observed fringes at the data points were introduced;The accuracy evaluation indicated that the first 4 terms of Williams equations are sufficient to describe the stress field in the vicinity of the crack tip for both Mode I and Mixed Mode cases. It was found that the modified Westergaard equations or the first two terms of Williams equations cannot be used to extract Mixed Mode fracture parameters;The average values of the new experimental results, K(,I)/K(,Io) and K(,II)/K(,I), for the two-dimensional inclined edge cracked plates lie within the range of numerical solutions and previous experimental values. Variation of stress intensity factor along a circumference of a semi-circular surface crack in pure Mode I loading is similar to that predicted by a finite element solution, but at higher numerical values. New experimental solutions for K(,I)/K(,Io) and K(,II)/K(,I) at the maximum depth of the three-dimensional inclined semi-circular cracks are presented

Dynamic modeling and monitoring of bridge decks

Abstract available (p. iii

Development of a platform for simulating and optimizing thermoelectric energy systems

Thermoelectrics are solid state devices that can convert thermal energy directly into electrical energy. They have historically been used only in niche applications because of their relatively low efficiencies. With the advent of nanotechnology and improved manufacturing processes thermoelectric materials have become less costly and more efficient As next generation thermoelectric materials become available there is a need for industries to quickly and cost effectively seek out feasible applications for thermoelectric heat recovery platforms. Determining the technical and economic feasibility of such systems requires a model that predicts performance at the system level. Current models focus on specific system applications or neglect the rest of the system altogether, focusing on only module design and not an entire energy system. To assist in screening and optimizing entire energy systems using thermoelectrics, a novel software tool, Thermoelectric Power System Simulator (TEPSS), is developed for system level simulation and optimization of heat recovery systems. The platform is designed for use with a generic energy system so that most types of thermoelectric heat recovery applications can be modeled. TEPSS is based on object-oriented programming in MATLAB®. A modular, shell based architecture is developed to carry out concept generation, system simulation and optimization. Systems are defined according to the components and interconnectivity specified by the user. An iterative solution process based on Newton\u27s Method is employed to determine the system\u27s steady state so that an objective function representing the cost of the system can be evaluated at the operating point. An optimization algorithm from MATLAB\u27s Optimization Toolbox uses sequential quadratic programming to minimize this objective function with respect to a set of user specified design variables and constraints. During this iterative process many independent system simulations are executed and the optimal operating condition of the system is determined. A comprehensive guide to using the software platform is included. TEPSS is intended to be expandable so that users can add new types of components and implement component models with an adequate degree of complexity for a required application. Special steps are taken to ensure that the system of nonlinear algebraic equations presented in the system engineering model is square and that all equations are independent. In addition, the third party program FluidProp is leveraged to allow for simulations of systems with a range of fluids. Sequential unconstrained minimization techniques are used to prevent physical variables like pressure and temperature from trending to infinity during optimization. Two case studies are performed to verify and demonstrate the simulation and optimization routines employed by TEPSS. The first is of a simple combined cycle in which the size of the heat exchanger and fuel rate are optimized. The second case study is the optimization of geometric parameters of a thermoelectric heat recovery platform in a regenerative Brayton Cycle. A basic package of components and interconnections are verified and provided as well

Generalized averaged Gaussian quadrature and applications

A simple numerical method for constructing the optimal generalized averaged Gaussian quadrature formulas will be presented. These formulas exist in many cases in which real positive GaussKronrod formulas do not exist, and can be used as an adequate alternative in order to estimate the error of a Gaussian rule. We also investigate the conditions under which the optimal averaged Gaussian quadrature formulas and their truncated variants are internal

MS FT-2-2 7 Orthogonal polynomials and quadrature: Theory, computation, and applications

Quadrature rules find many applications in science and engineering. Their analysis is a classical area of applied mathematics and continues to attract considerable attention. This seminar brings together speakers with expertise in a large variety of quadrature rules. It is the aim of the seminar to provide an overview of recent developments in the analysis of quadrature rules. The computation of error estimates and novel applications also are described

The stability of a model galaxy.

Thesis. 1976. Ph.D.--Massachusetts Institute of Technology. Dept. of Mathematics.Microfiche copy available in Archives and Science.Bibliography: leaves 203-204.Ph.D

PSA 2016

These preprints were automatically compiled into a PDF from the collection of papers deposited in PhilSci-Archive in conjunction with the PSA 2016

Computer Science Research Institute 2004 annual report of activities.

This report summarizes the activities of the Computer Science Research Institute (CSRI) at Sandia National Laboratories during the period January 1, 2004 to December 31, 2004. During this period the CSRI hosted 166 visitors representing 81 universities, companies and laboratories. Of these 65 were summer students or faculty. The CSRI partially sponsored 2 workshops and also organized and was the primary host for 4 workshops. These 4 CSRI sponsored workshops had 140 participants--74 from universities, companies and laboratories, and 66 from Sandia. Finally, the CSRI sponsored 14 long-term collaborative research projects and 5 Sabbaticals

Mechanical Instabilities of Soft Materials: Creases, Wrinkles, Folds, and Ridges

Subject to a sufficiently large compression, materials may undergo mechanical instabilities of various types. When the material is homogeneous, creases set in. When the material is a bilayer consisting of a stiff thin film on a thick compliant substrate, wrinkles set in. Creases are localized self-contact regions with large strain deviating from the smooth state, while wrinkles are undulations finite in space with infinitesimal strain deviating from the smooth state. After the formation of wrinkles, if the compression further increases, wrinkles double their period and form localized folds. If the substrate is subject to a sufficiently large pre-tension, wrinkles transit to ridges. This thesis explores different types of mechanical instabilities: creases, wrinkles, folds, and ridges. We start with studying creases in different materials. Soft tissues growing under constraint often form creases. We adopt the model of growth that factors the deformation gradient into a growth tensor and an elastic deformation tensor, and show that the critical conditions for the onset of creases take a remarkably simple form. We then perform simulations to explore creases in strain-stiffening materials. For a solid that stiffens steeply at large strains, as the compression increases, the surface is initially smooth, then forms creases, and finally becomes smooth again. For a solid that stiffens steeply at small strains, creases never form for all levels of compression. In order to better control the formation and disappearance of creases, we design a soft elastic bilayer with same moduli of the film and substrate but the substrate pre-compressed, and show that the bilayer can snap between the flat and creased states reproducibly with tunable hysteresis in a large strain range. We also show that an interface between two soft materials can form creases under compression. We then investigate the critical conditions for the onset of wrinkles and creases in bilayers with arbitrary thicknesses and moduli of the two layers, and show several new types of bifurcation behavior when the film and substrate have comparable moduli and thicknesses. We study the effect of substrate pre-stretch on post-wrinkling bifurcations, and show that pre-tension stabilizes wrinkles while pre-compression destabilizes wrinkles. When the pre-compression is sufficiently large, `chaotic' morphologies emerge. When the pre-tension is sufficiently large, we realize ridge localizations and networks under an equi-biaxial compression, and study the mechanics of ridge formation and propagation.Engineering and Applied Science

Aeronautical engineering: A cumulative index to a continuing bibliography (supplement 235)

This publication is a cummulative index to the abstracts contained in Supplements 223 through 234 of Aeronautical Engineering: A Continuing Bibliography. The bibliographic series is compiled through the cooperative efforts of the American Institute of Aeronautics and Astronautics (AIAA) and the National Aeronautics and Space Administration (NASA). Seven indexes are included -- subject, personal author, corporate source, foreign technology, contract number, report number and accession number