Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Bibliography: leaves 204-211. / by Thomas Dale Ketcham. / Sc.D.

Bibliography: leaves 240-257. / xvii, 274 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The main objective of this research is to develop a fundamentally new fatigue design and assessment procedure which can be used to predict the variation in crack size, strength and inspection periods as well as endurances. Basic fracture mechanics and fatigue procedures are used to illustrate this new technique. / Thesis (Ph.D.)--University of Adelaide, Depts. of Civil & Environmental Engineering and Mechanical Engineering, 1997?

Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: Anette M. Karlsson, Dept. of Mechanical Engineering. Includes bibliographical references.

We present an a-posteriori method for computing rigorous upper and lower bounds of the J-integral in two dimensional linear elasticity. The J-integral, which is typically expressed as a contour integral, is recast as a surface integral which yields a quadratic continuous functional of the displacement. By expanding the quadratic output about an approximate finite element solution, the output is expressed as a known computable quantity plus linear and quadratic functionals of the solution error. The quadratic component is bounded by the energy norm of the error scaled by a continuity constant, which is determined explicitly. The linear component is expressed as an inner product of the errors in the displacement and in a computed adjoint solution, and bounded using standard a-posteriori error estimation techniques. The method is illustrated with two fracture problems in plane strain elasticity. / Singapore-MIT Alliance (SMA)

Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 202-206).

Thesis (Naval Engineers Degree and M.S. in Mechanical Engineering)--Massachusetts Institute of Technology, 2002. / Includes bibliographical references (leaf 47). Also available online.

Thesis (M. Phil.)--University o9f Hong Kong, 1989.

Defect assessment against fracture initiated failure is carried out using fracture characterising parameters determined under quasi-static rates of loading. In practice, however, there are many instances where much higher loading rates prevail such as collision, blast and earthquake damage; and in transport. For these situations the rate sensitivity of the material to fracture should be considered. Fracture toughness tests (COD) have been conducted on C-Mn steel weld metal over a range of temperature and loading rates. The effect of increased loading rates is to reduce the crack-opening displacement whilst changing the fracture behaviour, such change being accompanied by an increase in the ductile-brittle transition temperature. Thermally activated flow is found to be the predominant mechanism governing plastic flow at intermediate strain-rates. It is then possible to evaluate the effect of strain-rate and temperature on the yield strength as a function of rate parameter kT 1n (A/ε), based on the Arrhenius equation. An attempt is presented to model the influence of temperature and loading rate on the fracture initiation toughness, COD. It may be fairly said that numerical results quite well describe the behaviour of the experimentally determined variation of COD with temperature and loading rate over the range 0.1 < K < 10⁶MPam^{1/2 s}^-1 and O < T < 500^oK. Thus, it has been demonstrated that the constitutive surface δI (T, K_I) can be produced numerically using the constitutive relation σy (ε,ε, T). Consideration of the defect sizes for engineering critical assessment showed that a significant reduction in maximum allowable defect size, bar a_max can result as a consequence of increased loading rate.

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In this dissertation, first the experimental and theoretical observations on the deformational characteristics of brittle geomaterials are reviewed and discussed. A basic conclusion is that special features such as strain softening can not be considered as true material (continuum) properties. These conclusions created a renewed emphasis on the constitutive modelling of such materials. A model that accounts for structural changes is developed. Such changes are incorporated in the theory through a tensor form of a damage variable. It is shown subsequently that formation of damage is responsible for the degradation in strength (softening) observed in experiments, for the degradation of the elastic shear modulus and for mechanical, damage induced anisotropy. A generalized plasticity model is incorporated for the so-called topical or continuum part of the behavior, whereas the damage part is represented by the so-called stress-relieved behavior. The question of uniqueness in the strain-softening regime is examined. It is shown that the constitutive equations lead to a unique solution for the case of rate dependent as well as rate independent formulation. Its implementation in finite element analysis shows mesh size insensitivity in the hardening and softening regimes. The general order of bifurcation of differential equations is employed in order to study the effect of damage accumulation on formation of narrow, so-called shear bands. It is shown that as the damage accumulates, the material approaches localization of deformation. The theory of mixtures is employed for further theoretical establishment of the proposed model. Energy considerations show the equivalence of the two-component damage body to an elastoplastic body containing cracks; the equivalence is considered in the Griffith sense. The mechanisms of failure are considered and discussed with respect to multiaxial stress pads. An explanation of failure, at the micro level, is given. The material constants involved in the theory are identified and determined from available experimental data. The model is then verified by back-predicting the observed behavior.