| Philosophical Transactions: Physical Science and Engineering; High- Temperature Structural Materials. Volume 351, Number 1697 |
15 JUN 95 |
216 pages |
| Authors:
R. W. Cahn; A. G. Evans; M. McLean; IMPERIAL COLL OF SCIENCE TECHNOLOGY ANDMEDICINE LONDON (UNITED KINGDOM)
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 | The Final Proceedings for High Temperature Structural Materials was held from 2 November 1994 to 3 November 1994. |
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| Mechanical Performance of Fiber Reinforced Metal Matrix Composites and Microstructural Development of Polycrystalline Alumina Fibers Synthesized from Liquid Precursors |
31 DEC 94 |
8 pages |
| Authors:
A. G. Evans; F. Zok; C. G. Levi; F. F. Lange; CALIFORNIA UNIV SANTA BARBARA
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| The research of the Office of Naval Research grant at UCSB focused on the research concerns of mechanical properties of fiber reinforced metal matrix composites as well as the understanding of microstructural development in polycrystalline Al2O3 fibers synthesized from liquid precursors. It has been closely coordinated with the DARPA/ONR URI program dealing with the design of high performance composites. |
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| A Knowledge Highway for Integrated Modelling from Manufacturing to Design |
30 NOV 94 |
44 pages |
| Authors:
A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| A workshop was held to discuss a new paradigm for choosing the preferred materials and processes needed for manufacturing a component, based on an analysis of the targeted attributes, performance and cost. This paradigm was developed around the idea of a 'knowledge highway'--a disciplined process for generating, storing and using the Information most relevant to the manufacturing and design engineers. Model systems were used to develop this Idea, which combined ... |
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| Fiber Coating Concepts for Brittle Matrix Composites |
93 |
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| Authors:
J. B. Davis; J. P. A. Loefvander; A. G. Evans; E. Bischoff; M. L. Emiliani; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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 | This study investigates a system of sapphire fiber-reinforced alumina. the system is thermochemically stable for severe conditions. it also exhibits little thermal expansion mismatch and utilizes the excellent strength and creep resistance of sapphire reinforcements. newly developed mechanical testing techniques for determining the interfacial fracture energies and sliding resistances were used to identify porous oxide and refractory metal coatings. |
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| The Ultimate Tensile Strength of Metal and Ceramic-Matrix Composites |
93 |
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| Authors:
M. Y. He; A. G. Evans; W. A. Curtin; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| The tensile strength of ceramic and metal matrix composites is subject to an important role of the fiber/matrix interface. the mechanical properties of this interface dictate the stress concentration that develops in fibers that surround a failed fiber. an analysis of this phenomenon is used to illustrate interface conditions that sufficiently diminish the stress concentration that a global load sharing criterion may be used to prescribe the contribution of the ... |
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| Cracking and Damage Mechanisms in Ceramic/Metal Multilayers |
93 |
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| Authors:
M. C. Shaw; D. B. Marshall; M. S. Dadkhah; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| Investigations of cracking in multilayered ceramic/metal composites are presented. two aspects are considered. they are subsequent crack extension and crack renucleation across intact single metal layers. subsequent crack progression occurs either by the formation of a zone of periodically spaced cracks or by the extension of a dominant, nearly planar crack. both patterns are analyzed. crack renucleation criteria are determined and compared with predictions. high-resolution strain-mapping techniques are employed to ... |
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| Effects of Misfit Strain and Reverse Loading on the Flow Strength of Particulate-Reinforced Al Matrix Composites |
93 |
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| Authors:
S. M. Pickard; S. Schmauder; D. B. Zahl; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| To critically assess flow models, experimental studies conducted on particulate-reinforced al alloys are used. for this purpose, the influence of thermal expansion misfit and of reverse loading provide a particularly critical assessment. comparison with models indicates that continuum cell calculations provide good predictions of trends, subject to an in situ matrix strength that may differ from that for the unreinforced alloy. |
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| Environmentally Compatible Double Coating Concepts for Sapphire Fiber- Reinforced Gamma-TiAl |
93 |
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| Authors:
T. J. Mackin; J. Y. Yang; C. G. Levi; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| Environmentally compatible interfaces based on double coating concepts have been developed for sapphire fibers in gamma-tial matrix composites. the fiber coating design involves two layers with distinct functions: one in contact with the fiber which provides the debonding and sliding characteristics required for toughening, and a second one next to the matrix which protects the fiber and debond layer from diffusional interactions and mechanical degradation during processing. three double coating ... |
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| Composites: Materials of the Future |
31 OCT 92 |
7 pages |
| Authors:
A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| A diverse group from Europe and the U.S. were brought together to address broad aspects of composite systems, ranging from processing to design and Including novel concepts. One objective was to compare and contrast approaches used tor polymer-based systems with those for metal and ceramic systems. Another was to assess opportunities for new Initiatives. A third was to explore concurrent engineering Issues. Various generalizations can be made based on the ... |
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| The Effect of Reinforcement Size on the Creep Strength of Intermetallic Matrix Composites |
92 |
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| Authors:
J. Roesler; A. G. Evans; MAX-PLANCK-INST FUER METALLFORSCHUNG STUTTGART (GERMANY F R)
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| The creep strengthening of intermetallic materials by reinforcements is shown to be limited owing to diffusional matter transport along the reinforcement/matrix interface. In order to avoid strength reduction by fast diffusion, a critical reinforcement size has to be exceeded which depends on the loading conditions (temperature, strain rate) of the composite. The required particle dimensions are identified in this article, comparing the rate of diffusive matter transport with the applied ... |
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| The Effect of Reinforcement Size on the Creep Strength of Intermetallic Matrix Composites |
92 |
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| Authors:
J. Rosler; A. G. Evans; MAX-PLANCK-INST FUER METALLFORSCHUNG STUTTGART (GERMANY F R) INST FUER WERKST OFFWISSENSCHAFTEN
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| The creep strengthening of intermetallic materials by reinforcements is shown to be limited owing to diffusional matter transport along the reinforcement/matrix interface. In order to avoid strength reduction by fast diffusion, a critical reinforcement size has to be exceeded which depends on the loading conditions (temperature, strain rate) of the composite. The required particle dimensions are identified in this article, comparing the rate of diffusive matter transport with the applied ... |
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| Effects of Misfit Strain and Reverse Loading on the Flow Strength of Particulate-Reinforced Al Matrix Composites |
92 |
|
| Authors:
S. M. Pickard; S. Schmauder; D. B. Zahl; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| To critically assess flow models, experimental studies were conducted on particulate-reinforced al alloys. the influence of thermal expansion misfit and reverse loading provide a particularly useful evaluation model. a comparison of results with models indicates that continuum cell calculations provide good predictions of trends, subject to an in-situ matrix strength that may differ from that for the unreinforced alloy. |
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| The Mode I Fracture Resistance of Unidirectional Fiber-Reinforced Aluminum Matrix Composites |
92 |
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| Authors:
H. C. Cao; J. Yang; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA COLL OF ENGINEERING
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| Mode I fracture resistance has been measured for an al/4 mg and al matrix composites. the material was unidirectionally reinforced with ceramic fibers, prepared using a squeeze casting technique. investigations were also made into the effects that sic particle additions have. the al matrix system had a relatively low fracture resistance, whereas the al/5 mg system had a high toughness. the addition of particulates slightly decreased the resistance to crack ... |
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| The Mechanical Properties of Al Alloys Reinforced With Continuous Al2O3 Fibers |
92 |
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| Authors:
M. S. Hu; J. Yang; H. C. Cao; A. G. Evans; R. Mehrabian; CALIFORNIA UNIV SANTA BARBARA COLL OF ENGINEERING
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| This paper covers the mechanical properties of aluminum matrix composites unidirectionally reinforced with al2o3 fibers. the measurements and characterization was done with longitudinal and transverse tension, as well as in shear. the flow strengths in transverse tension and shear are found to exceed those of the matrices. it was found that ductilities where lower. subject to the in-situ properties of the matrix being known from independent measurements, the strengthening is ... |
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| Design, Analysis and Application of an Improved Push-Through Test for the Measurement of Interface Properties in Composites |
92 |
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| Authors:
P. D. Warren; T. J. Mackin; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| An improved fiber push-through test has been designed and used to obtain new information about interfaces in composites consisting of matrices of a ti alloy and a borosilicate glass, both reinforced with sic fibers. interpretation of these results is accomplished through an analysis of coupled debonding and push-through, followed by push-back. the sliding stress is found to vary with push-out distance and to be substantially reduced in the vicinity of ... |
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| Effects of Fiber Roughness on Interface Sliding in Composites |
92 |
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| Authors:
T. J. Mackin; P. D. Warren; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| The presence of asperities at the fiber-matrix interface is noted experimentally as a load rise during the initial stages of push-out and as a reseating load drop during push-back. these effects are modeled by considering the elastic deformation of asperities at the interface. during fiber sliding, the decorrelation of initially matching fiber and matrix geometries results in an asperity pressure at the interface. fractal models of interface roughness are incorporated ... |
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| A High-Toughness Gamma-Titanium Aluminde |
92 |
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| Authors:
H. E. Deve; A. G. Evans; D. S. Shih; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| A high-toughness gamma-tial with a lath microstructure has been characterized. the presence of a laminated structure that consists of x(sub 2) plates between gamma laths has been shown to govern the toughness. the lath microstructure promotes dissipation through a combination of process zone and crack bridging mechanisms. mechanical twinning in the gamma-phase contributes to the toughness through the formation of a twin process zone, while regions consisting of intact lath ... |
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| The Mechanical Properties of Ceramic Composites Produced by Melt Oxidation |
92 |
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| Authors:
S. M. Pickard; E. Manor; H. Ni; A. G. Evans; R. Mehrabian; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| Measurements of strength and fracture toughness of a range of DIMOX materials, with and without SiC particulates, were taken. The SiC particulate size has been shown to correlate with strength, and to be consistent with a model based on the expansion misfit between the particulates and the matrix. The toughness has contributions for both the residual alloy and the silicon carbide. The residual alloy has been shown to conform well ... |
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| Fracture Characteristics of Ceramic-Matrix Composites |
92 |
|
| Authors:
A. G. Evans; CALIFORNIA UNIV SANTA BARBARA COLL OF ENGINEERING**
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| Ceramic matrix composites exhibit macroscopic fracture characteristics similar to those encountered with polymer matrix composites. However, the damage mechanisms involved and the micromechanics that represent the material behavior are substantially different. The macroscopic mechanical behavior involves well defined mode I, mode II, and mixed mode cracking response. The incidence of these responses depends on the particular composite. Most of the published literature is on composites with dense matrices consisting of ... |
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| The Role of Fiber Bridging in the Delamination Resistance of Fiber- Reinforced Composites |
92 |
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| Authors:
S. M. Spearing; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| Delamination cracks in composites may interact with misaligned or inclined fibers. Such interactions often lead to fiber bridging, which causes the nominal delamination resistance to increase as the crack extends. Substantial specimen geometry effects are also involved. An experimental investigation of the role of fiber bridging has been conducted for three different composites. The results are compared with fiber bridging models based on a softening traction law, leading to schemes ... |
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| Effects of Fiber Roughness on Interface Sliding in Composites |
92 |
|
| Authors:
T. J. Mackin; P. D. Warren; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| The presence of asperities at the fiber matrix interface is noted experimentally as a load rise during the initial stages of push out and as a reseating load drop during push back. These effects are modeled by considering the elastic deformation of asperities at the interface. During fiber sliding, the decorrelation of initially matching fiber and matrix geometries results in an asperity pressure at the interface. Fractal models of interface ... |
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| Design, Analysis and Application of an Improved Push-Through Test for the Measurement of Interface Properties in Composites |
92 |
|
| Authors:
P. D. Warren; T. J. Mackin; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
| An improved fiber push-through test has been designed and used to obtain new information about interfaces in composites consisting of matrices of a Ti alloy and a borosilicate glass, both reinforced with SiC fibers. Interpretation of these results is accomplished through an analysis of coupled debonding and push-through, followed by push-back. The sliding stress is found to vary with push-out distance and to be substantially reduced in the vicinity of ... |
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| Thin Film Cracking and the Roles of Substrate and Interface |
92 |
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| Authors:
T. Ye; Z. Suo; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| Cracks in thin films caused by residual tension are examined. Attention is focused on film cracking, subject to either interface debonding or substrate cracking. For crack channeling along the film, the driving force is found to depend on the channel cross-section, as governed by the fracture properties of the interface and the substrate, in addition to known effects of film thickness, residual stress and elastic moduli. The critical film thickness ... |
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| Interfaces between Alumina and Platinum: Structure, Bonding and Fracture Resistance |
92 |
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| Authors:
M. De Graef; B. J. Dalgleish; M. R. Turner; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| Various diffusion bonded interfaces have been produced between Pt and either sapphire or polycrystalline Al2O3. The structure, bonding and fracture resistance of these interfaces have been examined, as well as the influence of intervening silicate phases, both amorphous and crystalline. It is found that the intrinsic fracture resistance gamma(sub i) of the Pt/sapphire interface is high, especially when Pt has an epitaxial orientation with respect to the sapphire. The fracture ... |
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| The Effect of Reaction Products on the Fracture Resistance of a Metal/ Ceramic Interface |
92 |
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| Authors:
A. Bartlett; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| Solid state diffusion bonds between a pell cara(Ti) alloy and Al2O3 have been used to study the effect of reaction products on the fracture resistance of a metal/ceramic interface. The reaction layer consists of brittle intermetallics, consistent with the Ti-pell cara-Al ternary phase diagram. The interface fracture energy gamma(sub i) was found to be dominated by periodic tunnel cracking of the reaction products, and was relatively insensitive to layer thickness, ... |
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| The Fracture Resistance of Metal/Ceramic Interfaces |
92 |
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| Authors:
A. G. Evans; B. J. Dalgleish; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| The effects of interface structure and microstructure on the fracture energy, gamma(sub i), of metal/ceramic interfaces are reviewed. Some systems exhibit a ductile fracture mechanism and others fail by brittle mechanisms. In the absence of either interphases or reaction products, gamma(sub i) is dominated by plastic dissipation (for both fracture mechanisms), leading to important effects of metal thickness, h, and yield strength, sigma(sub o). Additionally, gamma(sub i) is larger when ... |
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| Deformation of Nanoscale Cermets |
92 |
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| Authors:
A. G. Evans; J. P. Hirth; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| Cobalt-tungsten carbide cermets are protypical dual-phase composites wherein the metal is the minor phase (volume fraction, f(sub m) =0.1-0.2), but is continuous, because of capillarity effects at the interphase interfaces during sintering. The refinement of such composites into the nanometer size scale regime is of interest and indeed, has been achieved, with the expectation that nanoscale refinement will enhance such properties as hardness and tensile strength. The role of plastic ... |
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| Metal/Ceramic Interfaces: Relationships between Structures, Chemistry and Interfaces |
15 MAR 91 |
135 pages |
| Authors:
A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| Interface fracture resistance measurements have been conducted on metal/ceramic interfaces with and without reaction products. Both ductile and brittle interface fracture have been documented. Some effects of residual stress have also been investigated. The influence of thermal expansion misfit on the mechanical behavior of metal/ceramic bonded systems has been shown to be strongly governed by the sign of the misfit strain, its magnitude, the yield strength of the metal and ... |
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| Twin Toughening in Titanium Aluminide |
91 |
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| Authors:
H. E. Deve; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| The mechanical behavior of a gamma-TiAl that exhibits mechanical twinning has been studied ; compared with that of other gamma-TiAl materials, which do not twin this material has been shown to have a relatively high toughness; the tough material forms a wide twin process zone upon crack propagation; the toughening is believed to be related to the non-linear deformation in the process zone created by twinning. |
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| Toughening of MoSi2 With a Ductile (Niobium) Reinforcement |
91 |
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| Authors:
T. C. Lu; A. G. Evans; R. J. Hecht; R. Mehrabian; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| The effect of the interfacial reactions and Y2O3 coatings on toughening of MoSi2 by ductile phase Nb reinforcements is studied; the interfacial reaction layer shows parabolic growth with Mo5Si3, (Mo, Nb)5Si3, and Nb5Si3 phases forming in the absence of coating; the ductile phase deformation is partially constrained, with debonding within the interfacial reaction zone, for precracked laminates subjected to tensile loads; more extensive debonding is a result of dense Y2O3 ... |
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| The Role of Interfaces in Fiber-Reinforced Brittle Matrix Composites |
91 |
|
| Authors:
A. G. Evans; F. W. Zok; J. Davis; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| The dominant influence of fiber coatings on the mechanical performance of brittle matrix composites is addressed. These effects are described in terms of two independent mechanical parameters, the debond energy, Gama sub i, and the sliding resistance along the debond, tau. Complications associated with mode mixity, roughness and coating microstructure are emphasized. A mechanics of composite behavior based on these parameters is described, together with measurement approaches that allow Gama ... |
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| The Anisotropic Mechanical Properties of a Ti Matrix Composite Reinforced With SiC Fibers |
91 |
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| Authors:
S. Jansson; H. E. Deve; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MECHANICAL AND ENVIRONMENTAL ENGINEERIN G
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| The anisotropic mechanical properties of a ti alloy composite reinforced with sic fibers have been investigated and rationalized using analytical models. the appropriate material model for this composite involves the following features; an interface that debonds and slides, a flaw insensitive ductile matrix, and high-strength elastic fibers subject to residual compressive stress caused by thermal expansion mismatch. this model is broadly consistent with the longitudinal, transverse, and shear properties of ... |
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| The Mechanical Behavior of a Hybrid Metal Matrix Composite |
91 |
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| Authors:
F. Zok; S. Jansson; A. G. Evans; V. Nardone; CALIFORNIA UNIV SANTA BARBARA DEPT OF MECHANICAL AND ENVIRONMENTAL ENGINEERIN G
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| The mechanical behavior of a unidirectionally reinforced hybrid metal matrix composite in two different states has been studied: one with a "weakly bonded" interface and the other with a "strong" interface. similarities and contrasts in mechanical behavior have been related to the properties of the interface. the longitudinal tensile strength and the crack growth initiation resistance are found to be insensitive to the condition of the interface. however, the material ... |
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| Mode I Fracture Resistance of a Laminated Fiber-Reinforced Ceramic |
91 |
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| Authors:
F. Zok; O. Sbaizero; C. L. Hom; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| The mode I fracture resistance of a ceramic matrix composite has been measured. Simultaneous observations have revealed that the resistance is dominated by frictional dissipation upon the pullout of fibers that fracture in the crack wake off the crack plane. Numerical and analytical crack growth simulations have been compared with the experimental results. One important feature in this comparison concerns the occurrence of large-scale bridging. With these effects taken into ... |
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| The Role of Interfaces in Fiber-Reinforced Brittle Matrix Composites |
91 |
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| Authors:
A. G. Evans; F. W. Zok; J. Davis; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
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| Residual Stress Cracking of Metal/Ceramic Bonds |
91 |
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| Authors:
A. Bartlett; A. G. Evans; M. Ruehle; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| Processing and Properties of Al2O3-Al Composites |
91 |
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| Authors:
B. D. Flinn; F. W. Zok; F. F. Lange; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| Metal-reinforced ceramic composites have been fabricated by infiltrating metal into ceramic pre-forms containing continuous open channels. The fracture resistance behavior of the composites has been characterized using both R curve measurements and work-of-rupture tests. The latter tests indicate that the steady state composite toughness is almost 10 MPa square root of m, a value which is about three times that of the ceramic matrix itself. The effect of matrix microstructure ... |
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| Sensor and Actuator Materials for High Performance Composites |
91 |
132 pages |
| Authors:
A. G. Evans; D. R. Clarke; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
| The residual stresses in sapphire fibers embedded in a number of ceramic and inter-metallic matrices are measured non-destructively and in-situ using the stress-induced frequency shift in fluorescence from chromium dopants in the fibers. The stresses as a function of depth into the fibers from the free surface are measured and from the depth profile we have determined the interfacial shear stresses between the fibers and the matrices. The stress distributions ... |
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| Zirconia Coatings for Sapphire Fiber-Reinforced Composites |
91 |
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| Authors:
J. B. Davis; E. Bischoff; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| Sapphire fibers are promising reinforcements for both ceramic and intermetallic matrices because of their high specific strength and stiffness as well as their superior creep resistance. These attributes can be utilized only if fiber coatings are identified to control the interfacial properties. The feasibility of employing ZrO2 coatings, which are thermochemically compatible with sapphire, was determined on the basis of fiber debonding requirements. In general, two types of behavior are ... |
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| Residual Stress Cracking of Metal Ceramic Bonds |
91 |
|
| Authors:
A. G. Evans; A. Bartlett; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| Metal/ceramic bonds subject to residual stress caused by thermal expansion misfit have been investigated in an Al2O3/Ta(Ti) system. The residual stresses cause cracking of either the Al2O3 or the interface, dependent on the magnitude and sign of the residual stress. The observed locations, orientations, and trajectories of the cracks have been rationalized on the basis of residual stress fields, energy release rates and fracture energies for the ceramic and the ... |
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| The Strength and Fracture of Metal/Ceramic Bonds |
91 |
|
| Authors:
M. Y. He; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
| The fracture strength of ceramic boned with metals is limited by the presence of stress concentrations that arise around the bond, especially near edges. Yet, in some cases, fracture can be induced to occur in the ceramic away from the bond. Analysis of the combined effect of elastic mismatch, plasticity and thermal expansion misfit is presented in this paper, to provide understanding of the trends in bond strength. Important influences ... |
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| The Fracture Resistance of a Model Metal/Ceramic Interface |
91 |
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| Authors:
I. E. Reimanis; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| Crack propagation has been measured for the Al2O3/Au interface subject to conditions that exclude stress corrosion. Crack growth has been shown to occur with a rising resistance, governed by intact metal ligaments in the crack wake. The level of resistance also increases as the metal layer thickness increases. Crack extension occurs by a combination of plastic void growth and interface debonding. The fracture energies are much larger than the work ... |
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| The Fracture Resistance of Metal/Ceramic/Intermetallic Interfaces |
91 |
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| Authors:
A. G. Evans; A. Bartlett; J. B. Davis; B. D. Flinn; M. Turner; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
| A concentrated effort on the mechanics of interface cracks, coupled with the development of test methods for measuring the interface fracture resistance, has provided a framework for characterizing the mechanical properties of interfaces. There appear to be four governing issues. i) Interface fracture can be either brittle or ductile. ii) The fracture resistance is strongly influenced by the loading mixity, primarily through its influence on the crack path. iii) Crack ... |
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| Powder Processing of Ceramic Matrix Composites |
91 |
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| Authors:
A. G. Evans; F. F. Lang; D. C. Lam; O. Sudre; B. D. Flinn; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
| Powder processing of ceramic matrix composites is reviewed with emphasis on 1) forming powder compacts containing reinforcements, 2) effect of the reinforcement network on the shrinkage and strengthening of the powder matrix during a heat treatment, 3) a novel for producing a metal reinforced ceramic composite and 4) a novel method for producing a laminar ceramic composite containing brittle fibers. Preliminary properties for the two new composite processing methods are ... |
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| Effects of Plasticity on the Crack Propagation Resistance of a Metal/ Ceramic Interface |
91 |
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| Authors:
I. E. Reimanis; B. J. Dalgleish; M. Brahy; M. Ruehle; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| Fracture experiments have been conducted on a gold/sapphire interface whose interface is found to fail by interface separation in a nominally "brittle" manner with a critical strain energy release rate, G(sub c) = 50 J/sq m, substantially larger than the work of adhesion, W(sub ad)= 0.5 J/sq m. Evidence of plastic deformation on the gold fracture surface, such as blunting steps and slip steps, suggest that plastic dissipation is the ... |
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| The Fracture Resistance of a Model Metal/Ceramic Interface |
91 |
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| Authors:
I. E. Reimanis; B. J. Dalgleish; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
| Crack propagation has been measured for the Al2O3/Au interface to conditions that exclude stress corrosion. Crack growth has been shown to occur with a rising resistance, governed by intact metal ligaments in the crack wake. The level of resistance also increases as the metal layer thickness increases. Crack extension occurs by a combination of plastic void growth and interface debonding. The fracture energies are much larger than the work of ... |
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| The Strength and Fracture of Metal/Ceramic Bonds |
91 |
|
| Authors:
M. Y. He; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
| The fracture strength of ceramics bonded with metals is limited by the presence of stress concentrations that arise around the bond, especially near edges. Yet, in some cases, fracture can be induced to occur in the ceramic away from the bond. Analysis of the combined effect of elastic mismatch, plasticity and thermal expansion misfit is presented in this paper, to provide understanding of the trends in bond strength. Important influences ... |
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| The Fracture Energy of Bimaterial Interfaces |
SEP 90 |
|
| Authors:
A. G. Evans; M. Ruhle; B. J. Dalgleish; P. G. Charalambides; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
|
| This article describes a framework applicable to the measurement and interpretation of the fracture energy, Gamma sub i, of bimaterial interfaces. A major conclusion of this study is that the fracture energy is not unique and usually exhibits values substantially larger than the thermodynamic 'work of adhesion.' The lack of uniqueness is related to mode mixity (shear/opening) effects experienced by interface cracks, as characterized by the phase angle of loading, ... |
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| Ductile Reinforcement Toughening of Gamma-TiAl: Effects of Debonding and Ductility |
90 |
|
| Authors:
H. E. Deve; A. G. Evans; G. R. Odette; R. Mehrabian; M. L. Emiliani; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| The effects of reinforcement debonding have been examined either by the development of a brittle reaction product layer or by depositing a thin oxide coating between the reinforcement and matrix; work hardening has been explored by comparing a Nb reinforcement that exhibits high work hardening with a solution hardened Ti-Nb alloy that exhibits negligible work hardening on ductile reinforcement toughening of gamma-TiAl; high work rupture is encouraged by extensive debonding ... |
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| Effects of Plasticity on the Crack Propagation Resistance of a Metal/ Ceramic Interface |
90 |
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| Authors:
I. E. Reimanis; B. J. Dalgleish; M. Brahy; M. Ruehle; A. G. Evans; CALIFORNIA UNIV SANTA BARBARA DEPT OF MATERIALS
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| Fracture experiments have been conducted on a gold/sapphire interface. The interface is found to fail by interface separation in a brittle manner. The critical strain energy release rate, G(sub c) =50 J/sq m, is substantially larger than the work of adhesion, W(sub ad) =0.5 J/sq m. Plastic dissipation is suggested as the primary contribution to the measured G(sub c), evidenced by plastic deformation on the gold fracture surface, such as ... |
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