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Dhirendra Kubair's blog

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Alternate expressions for the near-tip in-plane mixed-mode K-field stresses and displacements

Alternate expressions for the angular variation of the K-field stresses and displacements around a sharp-crack embedded in an elastic medium subjected to an in-plane mixed-mode (mode-1 and -2) loading are presented. The expressions are derived in terms of the mode-mixity angle instead of superposing the pure-mode fields. The alternate expressions are derived using complex potentials and the Kolosov-Muskhelishvili method. The mixed-mode stress and displacement fields are presented in the crack-tip Cartesian and polar coordinates. We have obtained the crack growth angle in terms of the mixity-angle assuming the maximum hoop- and principal-stress criterions.

 

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Doctoral (PhD) studentship available in Utah State University for Spring 2011

There are several  fully funded graduate student openings starting Spring 2011, in the
Department of Mechanical and Aerospace Engineering at the Utah State
University (http://www.mae.usu.edu).
The openings are in the broad area of Computational Solid Mechanics. In
particular, applicants having demonstrated interest (in terms of
completed projects, authorship in journal articles or coursework) in
Fracture Mechanics are especially invited. Applicants are requested to

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Graduate (PhD/MS) studentship available in Utah State University

There are several  fully funded graduate student openings in the Department of Mechanical and Aerospace Engineering at the Utah State University (http://www.mae.usu.edu). The openings are in the broad area of Computational Solid Mechanics. In particular, applicants having demonstrated interest (in terms of completed projects, authorship in journal articles or coursework) in Fracture Mechanics are especially invited.

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Mode-3 spontaneous crack propagation along functionally graded bimaterial interfaces

This is a paper that has been accepted for publication in the Journal of the Mechanics and Physics of Solids from our group. The paper describes the combined effect of material inertia and inhomogeneous material property variation on spontaneous cohesive-crack propagation in functionally graded materials. The preprint is attached as a PDF.

Abstract- The effects of combining functionally graded materials of different inhomogeneous property gradients on the mode-3 propagation characteristics of an interfacial crack are numerically investigated. Spontaneous interfacial crack propagation simulations were performed using the newly developed spectral scheme. The numerical scheme derived and implemented in the present work can efficiently simulate planar crack propagation along functionally graded bimaterial interfaces. The material property inhomogeneity was assumed to be in the direction normal to the interface. Various bimaterial combinations were simulated by varying the material property inhomogeneity length scale. Our parametric study showed that the inclusion of a softening type functionally graded material in the bimaterial system leads to a reduction in the fracture resistance indicated by the increase in crack propagation velocity and power absorbed. An opposite trend of increased fracture resistance was predicted when a hardening material was included in the bimaterial system. The cohesive tractions and crack opening displacements were altered due to the material property inhomogeneity, but the stresses ahead of the cohesive zone remained unaffected.

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Finite element simulations of microvoid growth due to selective oxidation in binary alloys.

Selective oxidation induced void growth is observed in thermal barrier coating (TBC) systems used in gas turbines. These voids occur at the interface between the bond coat and the thermally grown oxide layer. In this article we develop the modeling framework to simulate microvoid growth due to coupled diffusion and creeping in binary alloys. We have implemented the modeling framework into an existing finite element program. The developed modeling framework and program is used to simulate microvoid growth driven by selective oxidation in a binary beta-NiAl alloy. Axisymmetric void growth due to the combined action of interdiffusion and creeping is simulated. The sharpness of the void and direction of creeping are considered as parameters in our study. Our simulations show that the voids dilate without any change in shape when creeping is equally likely in all the directions (isotropic). Void growth patterns similar to those observed in experiments are predicted when the creeping is restricted to occur only along the radial and tangential directions. A hemispherical void grows faster compared to a sharp void. The sharpness increases in the case of a sharp void and could lead to interactions with the neighboring voids leading to spallation of the thermally grown oxide layer as observed in experiments.

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