Download or read book Research of Microstructurally Developed Toughening Mechanisms in Ceramics Stress Induced Transformation Toughening Part 1 Size Effects Associated with Constrained Phase Transformation Thermodynamics written by F. F. Lange and published by . This book was released on 1980 with total page 29 pages. Available in PDF, EPUB and Kindle. Book excerpt: The thermodynamics of the constrained phase transformation is presented with particular reference to size effects introduced by surface phenomena concurrent with the transformation, e.g., the formation of solid-solid surfaces (twins, etc.) and solid-vapor surfaces (e.g., microcracks). It is shown that these surface phenomena not only introduce a size-dependent energy term into the total free energy change, but also reduce the strain energy associated with the transformation, which can result in a transformation at a temperature where the chemical free energy change is less than the unrelieved strain energy associated with the constrained transformation. The results of this analysis lead to a phase diagram representation that includes the size of the transforming inclusion. This diagram can be used to define the critical inclusion size required to prevent the transformation and/or to obtain the transformation, but avoid one or more of the concurrent surface phenomena. (Author).
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1981 with total page 1370 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Download or read book Microstructurally Developed Toughening Mechanisms in Ceramics written by F. F. Lange and published by . This book was released on 1979 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt: The thermodynamics of a constrained transformation has been examined with regard to the conditions for phase retension during fabrication and the effect of a stress-induced transformation on the fracture toughness. Constraint of the shape change associated with the transformation by an elastic matrix will lower the transformation temperature. Retention also requires that a critical grain size (or particle size) cannot be exceeded during fabrication. Two binding solutions for the critical stress intensity factor (Kc) were obtained: one for the case where the transformation suffers no stress hysteresis effect and the other for a large stress hysteresis effect. Both indicate that Kc will depend on the transformation's shape change, the elastic properties of the constraining matrix, the volume fraction of the retained, metastable phase and temperature. Kc is predicted to decrease with increasing temperature. (Author).
Download or read book Technical Abstract Bulletin written by and published by . This book was released on 1981 with total page 204 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Research of Microstructurally Developed Toughening Mechanisms in Ceramics Part 2 Contribution to Fracture Toughness written by F. F. Lange and published by . This book was released on 1981 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt: The first part of this series described the thermodynamics of the constrained phase transformation with particular emphasis on the effect of the inclusion size. In this part, two different approaches, viz. Griffith's and Irwin's, will be used to determine the contribution of a stress-induced phase transformation to the fracture toughness of a brittle material. As in Part 1, special reference will be made to the ZrO2 (tetragonal) yields ZrO2 (monoclinic) transformation.
Download or read book Fracture Mechanics of Ceramics written by Richard Carl Bradt and published by Springer Science & Business Media. This book was released on 1983-08-31 with total page 698 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Research of Microstructurally Developed Toughening Mechanisms in Ceramics Parts 1 5 written by F. F. Lange and published by . This book was released on 1980 with total page 107 pages. Available in PDF, EPUB and Kindle. Book excerpt: Reseaech of microstructurally developed toughening mechanisms in ceramics: Part 1: Size effects associated with the thermodynamics of constrained transformations; Part 2: Contribution to fracture toughness; Part 3: Experimental observations in the ZrO2-Y2O3 system; Part 4: Fabrication, fracture toughness and strength of AL2O3/ZrO2 composite; Part 5: Effect of temperature and alloy on fracture toughness.
Download or read book Microstructurally Developed Toughening Mechanisms in Ceramics Stress Induced Martensitic Reaction II Experiments in the ZrO2 Y2O3 System written by F. F. Lange and published by . This book was released on 1978 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: Retention of the tetragonal phase was found to depend on both density and grain size. The dependence on density is consistent with the need for self-constraint and the concepts developed regarding the thermodynamics of the martensitic reaction in an elastically constrained system. The dependence on grain size and the effect of Y2O3 on the critical grain size is consistent with the theory relating the latent internal pressure (required to maintain equilibrium between the two structures) and the grain size to the thermodynamics of microcracking in a highly localized stress field. The contribution of the stress-induced transformation to the fracture toughness is significant and it is directly related to the volume fraction of the retained tetragonal phase. Theory developed to explain this contribution is in good agreement with experimental data validating the concept that the transformation's contribution lies with the work done by the crack's stress field to unconstrain the martensitic reaction. Fractography indirectly supports this concept and directly invalidates the concept of microcracking in advance of the primary crack as suggested by others. (Author).
Download or read book Research of Microstructurally Developed Toughening Mechanisms in Ceramics written by D. J. Green and published by . This book was released on 1982 with total page 80 pages. Available in PDF, EPUB and Kindle. Book excerpt: An approach is presented for predicting the strengthening of brittle materials by compressive surface stresses. The approach incorporates the effect of crack closure, which can significantly influence the stress intensity factor. The analysis is used for the example of tempering and it is found that the results give a better understanding of crack growth but also indicate approaches for optimization of the strengthening. Compressive surface stresses can be introduced into transformation-toughened Zr02 ceramics by grinding or impact. These techniques usually have associated damage effects. A new approach is introduced whereby surface compression is introduced by a heat treatment, which involves the removal of the oxide additives, that were originally introduced to retain the Zr02 in its tetragonal phase, from the surface region. The presence of the compressive surface stresses is confirmed and the ensuing improved resistance to indentation cracking is described. (Author).
Download or read book R D Abstracts written by Technology Reports Centre (Great Britain) and published by . This book was released on 1981 with total page 622 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Research of Microstructurally Developed Toughening Mechanisms in Ceramics Part 5 Effect of Temperature and Alloy on Fracture Toughness written by F. F. Lange and published by . This book was released on 1981 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: The critical stress intensity factor (Kc) of materials containing tetragonal ZrO2 was found to decrease with increasing temperature and CeO2 alloying additions, as predicted by theory. The temperature dependence of Kc was related to the temperature dependence of the chemical free energy change associated with the tetragonal yields monoclinic transformation. Good agreement with thermodynamic data available for pure ZrO2 was obtained when the size of the transformation zone associated with the crack was equated to the size of the ZrO2 grains. The Kc vs CeO2 addition data was used to estimate the tetragonal, monoclinic, cubic eutectoid temperature of 270 C in the ZrO2-CeO2 binary system. (Author).
Download or read book Research of Microstructurally Developed Toughening Mechanisms in Ceramics Part 3 Experimental Observations in ZrO2 Y2O3 System written by F. F. Lange and published by . This book was released on 1981 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: Materials in the ZrO2-Y2O3 system (less than or equal to 7.5 m/o Y2O3) were fabricated to investigate the conditions required to retain the metastable, tetragonal phase and to determine the contribution of the stress-induced martensitic reaction to fracture toughness. Retention of the tetragonal phase was optimized by minimizing porosity and maintaining the grain size below a critical valve. The critical grain size increased from 0.2 micrometers to 1 micrometer for compositions ranging between 2 m/o Y2O3 to 3 m/o Y2O3, respectively. These results are consistent with the theories developed regarding the thermodynamics of the martensitic reaction in a constrained state. In the tetragonal plus cubic phase field (compositions between 3.0 and 7.5 m/o Y2O3), the critical stress intensity factor decreased from 6.3 MPa.m1/2 to 3.0 MP.a1/2 as the volume fraction of the retained, tetragonal phase decreased to zero. Theoretical results, derived from the concept that the crack's stress field does work to unconstrain the transformation, are in good agreement with the experimental results. (Author).
Download or read book Research on Microstructurally Developed Toughening Mechanisms in Ceramics written by and published by . This book was released on 1983 with total page 50 pages. Available in PDF, EPUB and Kindle. Book excerpt: An approach is presented for predicting the strengthening of brittle materials by compressive surface stresses. The approach incorporates the effect of crack closure, which can significantly influence the stress intensity factor. The analysis is used for the example of tempering and it is found that the results give a better understanding of crack growth but also indicate approaches for optimization of the strengthening. Compressive surface stresses can be introduced into transformation-toughened Zr02 ceramics by grinding or impact. These techniques usually have associated damage effects. A new approach is introduced whereby surface compression is introduced by a heat treatment, which involves the removal of the oxide additives, that were originally introduced to retain the Zr02 in its tetragonal phase, from the surface region. The presence of the compressive surface stresses is confirmed and the ensuing improved resistance to indentation cracking is described. (Author).
Download or read book Energy Research Abstracts written by and published by . This book was released on 1984 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Microstructurally Developed Toughening Mechanisms in Ceramics Stress Induced Martensitic Reactions I Theory of Metastable Phase Retention and Contribution to Fracture Toughness written by F. F. Lange and published by . This book was released on 1978 with total page 31 pages. Available in PDF, EPUB and Kindle. Book excerpt: Prevention of a martensitic reaction is explained by relating the internal pressure, which arises through matrix constraint, to pressure-temperature-compositional phase equilibria. To have a constraint, microcracking must be avoided by fabricating the material with a grain/particle size less than a critical value. This is a previous result of theories concerned with crack extension in highly localized stress fields. The contribution of a stress-induced martensitic reaction to fracture toughness is explained in terms of the work done by the crack's stress field to overcome the matrix constraint. This analysis shows that the important factors contributing to the fracture toughness are the structural shape change, the elastic properties of the constraining materials, the volume fraction of the retained metastable phase, and the radius of the transformed zone at the crack front. (Author).
Download or read book Government Reports Announcements Index written by and published by . This book was released on 1981-07 with total page 1304 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Engineered Materials Abstracts written by and published by . This book was released on 1993-07 with total page 724 pages. Available in PDF, EPUB and Kindle. Book excerpt:
