35 research outputs found
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Long-term performance of ceramic matrix composites at elevated temperatures: Modelling of creep and creep rupture
The models developed, contain explicit dependences on constituent material properties and their changes with time, so that composite performance can be predicted. Three critical processes in ceramic composites at elevated temperatures have been modeled: (1) creep deformation of composite vs stress and time-dependent creep of fibers and matrix, and failure of these components; (2) creep deformation of ``interface`` around broken fibers; and (3) lifetime of the composite under conditions of fiber strength loss over time at temperature. In (1), general evolution formulas are derived for relaxation time of matrix stresses and steady-state creep rate of composite; the model is tested against recent data on Ti-MMCs. Calculations on a composite of Hi-Nicalon fibers in a melt-infiltrated SiC matrix are presented. In (2), numerical simulations of composite failure were made to map out time-to-failure vs applied load for several sets of material parameters. In (3), simple approximate relations are obtained between fiber life and composite life that should be useful for fiber developers and testers. Strength degradation data on Hi-Nicalon fibers is used to assess composite lifetime vs fiber lifetime for Hi-Nicalon fiber composites
The Role of Durability in Reliability-Based Design of Composite Materials for Civil Structures
Nano-mechanics Foundations and Experimental Methodologies for Multiphysics Prognosis of Functional Behaviour in Heterogeneous Functional Materials (HeteroFoaM)
AbstractThe present paper will discuss the nano-mechanics foundations and experimental methodologies that provide a foundation for the prognosis of the functional behavior of nano-structured heterogeneous materials for energy systems. The principle objective of this work at the fundamental level is the creation of conceptual foundations for prognosis of heterogeneous functional materials. Our approach is to focus on the mechanics associated with the nano-structural configurations and interfaces (function and geometry) of the active phases. The paper will discuss conceptual foundations, experimental methods, and computational and analysis methods that associate global functional response of interest to energy conversion and storage with the multiphysics of nano-structured heterogeneous materials. New experimental room-temperature, non-invasive interrogation methods for establishing internal integrity and for following material state changes in solid oxide fuel cells as a function of operation history will also be introduced and discussed as an example of the application of these concepts
Observation of Internal Damage and Inelastic Deformation of Graphite/Epoxy Tubes [±45°]4 under Cyclic Axial Loading
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Investigation of properties and performance of ceramic composite components: Final report on Phases 3 and 4
The objective of the Fossil Energy Advanced Research and Technology Development (AR and TD) Materials Program is to conduct research and development on materials for longer-term fossil energy applications as well as for generic needs of various fossil fuel technologies. The research program of the Materials Response Group at Virginia Tech addresses the need for reliable and durable structural ceramic composites to perform in high temperature environments. The research effort provides an experimental and analytical basis for the transition from properties of materials to performance of actual component structures. Phases 1 and 2 of the present program focused on the development of test capabilities, initial studies of component mechanical response under various conditions and the development of a life prediction methodology. These efforts have been described in previous reports. This report summarizes the major tasks completed under Phases 3 and 4 of the project. Overall, the authors have made significant progress in a broad spectrum of tasks in this program. Their efforts have encompassed component evaluation, assessment of new SiC-based composites with improved high-temperature potential, development of oxide coating materials for SiC, and the extension and development of new models for predicting the durability of composite components under specific operating conditions for various CMC applications. Each of these areas of work is an important area for achieving the ultimate goal of usable SiC-based composites in high-temperature corrosive environments typical of fossil energy applications
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Properties and Performance of Ceramic Composite Components
The objective of the Fossil Energy Advanced Research and Technology Development (AR and TD) Materials program is to conduct research and development on materials for longer-term fossil energy applications as well as for generic needs of various fossil fuel technologies. These needs have prompted research aimed toward a better understanding of material behavior in fossil energy environments and the development of new materials capable of substantial enhancement of plant operations, reliability, and efficiency