Minimal failure probability for ceramic design via shape control

We consider the probability of failure for components made of brittle mate- rials under one time application of a load as introduced by Weibull and Batdorf - Crosse and more recently studied by NASA and the STAU cooperation as an objective functional in shape optimization and prove the existence of optimal shapes in the class of shapes with a uniform cone property. The corresponding integrand of the objective functional has convexity properties that allow to derive lower-semicontinuity according to Fujii (Opt. Th. Appl. 1988). These properties require less restrictive regularity assumptions for the boundaries and state functions compared to [arXiv:1210.4954]. Thereby, the weak formulation of linear elasticity can be kept for the abstract setting for shape optimization as presented in the book by Haslinger and Maekinen

GivEn -- Shape Optimization for Gas Turbines in Volatile Energy Networks

This paper describes the project GivEn that develops a novel multicriteria optimization process for gas turbine blades and vanes using modern "adjoint" shape optimization algorithms. Given the many start and shut-down processes of gas power plants in volatile energy grids, besides optimizing gas turbine geometries for efficiency, the durability understood as minimization of the probability of failure is a design objective of increasing importance. We also describe the underlying coupling structure of the multiphysical simulations and use modern, gradient based multicriteria optimization procedures to enhance the exploration of Pareto-optimal solutions

Aeronautical Engineering: A special bibliography, supplement 60

This bibliography lists 284 reports, articles, and other documents introduced into the NASA scientific and technical information system in July 1975

Activities of the Structures Division, Lewis Research Center

The purpose of the NASA Lewis Research Center, Structures Division's 1990 Annual Report is to give a brief, but comprehensive, review of the technical accomplishments of the Division during the past calendar year. The report is organized topically to match the Center's Strategic Plan. Over the years, the Structures Division has developed the technology base necessary for improving the future of aeronautical and space propulsion systems. In the future, propulsion systems will need to be lighter, to operate at higher temperatures and to be more reliable in order to achieve higher performance. Achieving these goals is complex and challenging. Our approach has been to work cooperatively with both industry and universities to develop the technology necessary for state-of-the-art advancement in aeronautical and space propulsion systems. The Structures Division consists of four branches: Structural Mechanics, Fatigue and Fracture, Structural Dynamics, and Structural Integrity. This publication describes the work of the four branches by three topic areas of Research: (1) Basic Discipline; (2) Aeropropulsion; and (3) Space Propulsion. Each topic area is further divided into the following: (1) Materials; (2) Structural Mechanics; (3) Life Prediction; (4) Instruments, Controls, and Testing Techniques; and (5) Mechanisms. The publication covers 78 separate topics with a bibliography containing 159 citations. We hope you will find the publication interesting as well as useful

Influence of Microstructure on Damage Behavior of Sound Absorbing Ceramics

Porous sound-absorbing ceramics contribute to the passive damping of thermo-acoustic instabilities and sound dissipation. As ceramic liners, they must satisfy all requirements respecting mechanical strength and thermal resistance. Design and development of such ceramics concern various aspects like thermal shock resistance, crack behavior, fatigue limit, creep and erosion resistance. The aim of this work is to investigate the mechanical behavior of highly porous sound absorbing ceramics and to predict the brittle damage behavior considering the material microstructure. It studies the applicability of such ceramics as insulation liners for the combustion chambers and gives a clue to further material improvement in terms of mechanical strength. Experiments were performed in this work to characterize the mechanical strengths of a new developed sound absorbing ceramic for the application as ceramic heat shields for the combustion chambers of premixed gas turbines. Compressive tests at both room and high temperature as well as four-point bending tests at room temperature have been carried out. Furthermore, the fits of fracture strengths of the material to the Normal, Weibull and Type I extreme value distributions are investigated. The characterization was then expanded to other physical properties such as porosity, density, thermal conduction coefficients and thermal expansion coefficients. A non-multi-physic but multi-scale approach is applied in this work which predicts the influence of the microstructure on the macroscopic properties. The scale transition method is known as mean-field homogenization method, based on assumed relations between average values of micro-strain and -stress fields in each phase. This homogenization model is based on the Eshelby model and assumes the pores (or rather inclusions) to be ellipsoidal. Influence of the pore density, pore form and pore orientation on the strength of these porous sound absorbing ceramic are studied here. Depending on the loading condition higher strength by higher porosity values is achievable by for example aligning the pores on a desired direction or changing their form from spherical to ellipsoid with high aspect ratios. Furthermore, direct finite element simulations of a representative-volume element (RVE) are also implemented in this work to investigate the pure brittle damage of this sound absorbing ceramic. An effective-stress degradation model has been implemented in a predefined user-subroutine of ABAQUS. It is based on the three dimensional rupture criterion and describes the pure brittle damage under mechanical, thermomechanical, static and quasi-static loadings. Different RVE s have been generated and investigated in terms of damage considering different structural parameters. The present results demonstrate the application potential of these sound absorbing ceramic as liner in terms of mechanical strengths, predict their brittle damage behavior considering the microstructure and provide a base for further material developments and numerical investigations. The applicability of these ceramic to line the combustion chambers in terms of sound absorption is investigated on an experimental set-up at the Faculty of Combustion of the Center of Applied Space Technology and Microgravity (ZARM). The validation of the results from this chapter will be performed on this set-up