Strength and Notch Sensitivity of Porous‐Matrix Oxide Composites

Mattoni, Michael A.; Zok, Frank W.

doi:10.1111/j.1551-2916.2005.00299.x

Cited by 24 publications

(27 citation statements)

References 36 publications

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“…junction stiffness, weighted by the fraction of the three junction Using the arithmetic averaging method, the toughness is predicted types, given by Eq. (15). Both the arithmetic mean and the to be: harmonic mean are considered.…”

Section: Ii1 Materials and Test Procedures (1) Experimental Resultsmentioning

confidence: 99%

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Matrix-Enabled Damage Tolerance in Oxide CFCCs

Zok¹,

Levi²,

McMeeking³

2005

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The objective of this program has been to elucidate the underlying mechanisms by which porous matrices give rise to composite toughness in the absence of interphases between the fibers and the matrix, the role of microstructure and processing in attaining this behavior, and the mechanics associated with the deformation, cracking and failure of the composites. The broader goal has been to develop the knowledge base necessary to exploit the nonlinear phenomena occurring within the matrix. Properties of prime interest include in-plane tensile strength and notch sensitivity, subject to both fiber-dominated and matrix-dominated loadings. Recognizing that changes in the structure of the porous matrix have opposing effects on the properties of interest (enhancing some while compromising others), the research has sought to identify the microstructural parameters that provide a desirable balance of composite properties. The key variables explored were those pertaining to the characteristics of the porosity, notably its content, as well as the nature and extent of the bonds which determine both the strength of the particle network within the matrix and the strength of the fiber-matrix interface.The highlights of the program are summarized below. Additional details are in the appended papers. Mullite/Alumina Mixtures for Use as Porous MatricesWeakly bonded particle mixtures of mullite and alumina have been assessed as candidate matrices for use in porous matrix ceramic composites. Conditions for the deflection of a matrix crack at a fiber-matrix have been used to identify the combinations of modulus and toughness of the fibers and the matrix for which damage tolerant behavior is expected to occur in the composite. Accordingly, an experimental study on modulus and toughness of particle mixtures as well as the changes in these properties following aging at elevatedPublic reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instruct.ons, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. ABSTRACT (Maximum 200 Words)The program has focused on the mechanics of deformation and fracture of a family of porous-matrix all-oxide continuous fiber ceramic composites (CFCCs). The activities have lead to substantive developments in the mechanistic understanding of: (i) mechanical properties and thermal stability of porous mullite/alumina matrices; (ii) strength, fracture resistance and notch sensitivity of porous-matrix composites; and (iii) stability and performance of oxide composites in gas turbine combustion environments. Models to describe the pertinent phenomena have been developed and validated.14. 2 temperature was designed and conducted. Models for these properties based on bonded particle aggregates have been calibrated. Upon combining the experimental and modeling results, predictions are made of the critical aging times at which damage tolerance is lost because of ...

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Section: Ii1 Materials and Test Procedures (1) Experimental Resultsmentioning

confidence: 99%

“…In comparing Eq. tions from alumina-alumina, alumina-mullite, and mullite-mullite (15) to the experimental data, the remaining unknown variable. T1.…”

Section: Ii1 Materials and Test Procedures (1) Experimental Resultsmentioning

confidence: 99%

Matrix-Enabled Damage Tolerance in Oxide CFCCs

Zok¹,

Levi²,

McMeeking³

2005

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“…26 There was no apparent detrimental effect of the SiC particles. Because of limited material volume, tensile tests were performed on hourglassshaped specimens.…”

Section: Property Assessmentmentioning

confidence: 97%

Processing of Oxide Composites with Three‐Dimensional Fiber Architectures

Yang

Weaver

Zok

et al. 2009

Journal of the American Ceramic Society

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Fabrication of oxide fiber composites is accompanied by the development of drying cracks in the matrix following slurry infiltration. The cracks are a result of the inherent shrinkage in particle compacts during drying coupled with the mechanical constraints imposed on the matrix by the fibers. The effects are most pronounced in systems with three‐dimensional fiber architectures. A mitigation strategy based on the addition of coarse matrix particles to the fine particulates has been devised and demonstrated. Among the various implementation strategies explored, the most effective involves combining the two particle types (coarse and fine) into a single slurry and coinfiltrating the slurry through sequential vibration‐ and vacuum‐assisted processes. Regardless of the infiltration route, the SiC particles have no apparent detrimental effect on the fiber bundle properties. Additionally, they increase the through‐thickness thermal diffusivity by 50%–100%.

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“…Experimental measurements on three such materials, with varying matrix strength levels, and accompanying photographs of the tested specimens are shown in Figs. 20 and 21(a) 56 . As the strength of the matrix is increased (by addition of a precursor‐derived alumina within a particulate mullite–alumina matrix), the length of shear bands emanating from the notch tip and the extent of fiber pullout decrease dramatically.…”

Section: Notch Sensitivitymentioning

confidence: 99%

Developments in Oxide Fiber Composites

Zok

2006

Journal of the American Ceramic Society

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211

104

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Prospects for revolutionary design of future power generation systems are contingent on the development of durable high-performance ceramic composites. With recent discoveries in materials and manufacturing concepts, composites with all-oxide constituents have emerged as leading candidates, especially for components requiring a long service life in oxidizing environments. Their insertion into engineering systems is imminent. The intent of this article is to present a synopsis of the current understanding of oxide composites as well as to identify outstanding issues that require resolution for successful implementation. Emphasis is directed toward material systems and microstructural concepts that lead to high toughness and longterm durability. These include: the emergence of La monazite and related compounds as fiber-coating materials, the introduction of the porous-matrix concept as an alternative to fiber coatings, and novel strategies for enabling damage tolerance while retaining long-term morphological stability. Additionally, materials and mechanics models that provide insights into material design, morphology evolution, and composite properties are reviewed.

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Strength and Notch Sensitivity of Porous‐Matrix Oxide Composites

Cited by 24 publications

References 36 publications

Matrix-Enabled Damage Tolerance in Oxide CFCCs

Matrix-Enabled Damage Tolerance in Oxide CFCCs

Processing of Oxide Composites with Three‐Dimensional Fiber Architectures

Developments in Oxide Fiber Composites

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