Mode I solution for micron-sized crack

The feature size of micro-electronic, optoelectronic and biomedical devices is in the sub-micron scale and is pushing toward the nanometer scale. Defects in these small structures are correspondingly smaller such that small crack behavior is becoming an important design consideration for reliability and performance of such devices. Analyses of small cracks are complicated by the rapid variation in the deformation in the crack tip zone. Strain gradients in the near tip zone, which can be ignored in large cracks, will influence the small crack behavior when the crack tip zone is in the order of the crack size. In this paper, we consider two-dimensional crack deformations with strain gradient effect and establish the dual formulations in terms of potentials. The formulations reduce to the conventional linear elastic fracture theory, when the material length scale parameters for the higher order deformation measures are zero. One of the formulations is in terms of two complex stress functions and two pseudo potentials. The complex stress functions are harmonic and the governing equations for the pseudo-potentials are two uncoupled second order partial differential equations. The solutions for these equations are coupled through the boundary conditions.A perturbation method is used to construct the solution for mode I cracks under a K-field when only the effect of the rotational gradient is included. The perturbation solution has induced singularity for the stresses. The induced deformation decays exponentially away from the crack tip. The induced stresses become insignificant beyond 3ε, the typical characteristics of a boundary layer type. To a first order approximation, the induced deformation energy normalized by that of the classical solution under constant applied crack opening load is linearly proportional to ε. This implies that the induced energy release rate is linearly proportional to the length scale parameter. The induced energy release rate under a fixed crack opening load is negative indicating that the rotational gradient shields the crack and lowers the total deformation energy release rate for small crack.     

An integral-equation solution for cracked half-planes bonded together and containing debondings along their interface

The general solution of an arbitrary system of microdefects (i.e. cracks and/or holes) in an isotropic elastic half-plane bonded partially, along an infinite number of straight line segments to another half-plane consisting of a different isotropic elastic material, is formulated in this paper using the complex variable technique. The solution in terms of complex potentials is given by integrals over the cracks and/or holes with integrands expressed in terms of Green's functions and an unknown complex density function. Finally, the problem is reduced to the solution of a singular integral equation for the complex density function only along the microdefects. The appropriate Green's functions are derived from the solution of the problem of a concentrated force or a dislocation existing in either of the two half planes. Numerical results are presented for the stress intensity factors in three different cases.     

Analytical solution for orthotropic composite plate containing a mode I crack along principle axis

Analytical stress analyses are presented for orthotropic composite materials containing a through crack under uniaxial normal loads (mode I). A harmonic differential equation has been established for the orthotropic plates with axes normal to the three orthogonal planes of material symmetry by introducing new complex variables. The complex theory was employed to find stress functions to satisfy the equilibrium equation, compatibility equation and boundary condition at infinite and crack surfaces. An analytical solution was examined in the case of isotropic materials. It is demonstrated that the analytical solution obtained is correct for the orthotropic composite plates.     

An orthotropic sandwich plate containing a part-through crack under mixed mode deformation

An orthotropic sandwich plate containing a part-through crack subjected to in-plane mixed mode tractions is analyzed, and the basic equations for estimating the stress intensity factors $\text{k}{}_1$, $\text{k}{}_2$ and the debonding naion around the crack are presented.     

Twisting of an elastic plate containing a crack

The stress distribution caused by twisting an infinite plate containing a finite crack is analyzed in terms of Reissner's theory for the bending of thin plates. The singular character and the detailed structure of the stresses near the ends of the crack are determined in closed form. Numerical results are given for the magnitudes of the stress couples and stress resultants for a range of plate thicknesses.

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Zusammenfassung Due Spannungsvertcilung, hervorgerufen durch die Torsion einer unendlichen Platte mit einem Ri\ begrenzter Länge, wird mit Hilfe der Reissner-Theorie für die Biegebeanspruchung dünner Platten untersucht. Der singulare Charakter und die genauc Verteilung der Spannungen in Nähe der Ri\enden werden bestimmt. Zahlenmä\ige Ergebenisse für die Gro\e der Spannungsparre und ihrer Resultanten werden für eine Reihe von Plattenstärken angegeben.

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Résumé La distribution des contraintes dans une plague infinie comportant une fisure finic et soumise à torsion est analysée au moyen de la théorie de Reissner pour la flexion des tôles minces.Le caractère singulier, et la structure de détail des contraintes au voisinage des extrémités de la fisure sont explicités.Des résultats numériques sont fournis en ce qui regarde les grandeurs des couples de contraintes et de leurs résultantes, pour une certaine gamme d'éspaisseur de tôles.

     

An integral-equation formulation of nonlinear deformation in a stack of buffered plates

An integral-equation formulation has been derived for nonlinear deformation in a stack of buffered Kirchhoff plates. The plates are assumed to follow a nonlinear bending moment-curvature law and the buffer material to follow the generalized Hooke’s law. By employing the recently derived special Green’s function for multilayers with interfacial membrane and flexural rigidities as the kernel, the integral-equation formulation only involves the surface loading area (for application to an indentation problem) and the portion of plates undergoing nonlinear deformation. Based on the integral equation, an efficient and accurate boundary element method has been derived to numerically solve the cylindrical indentation problem of the material with a bilinear flexural bending law for the plates. Numerical examples are presented to show a progressive damage process of yielding across a stack of plates as well as to demonstrate the validity and accuracy of the present integral-equation formulation.     

An analysis of compressive stability of elastic solids containing a crack parallel to the surface

An analysis is presented for compressive stability of elastic solids containing a crack parallel to the free surface based on the mathematical theory of elasticity. Basic buckling equations derived from the mathematical theory of elasticity are employed and are reduced to a system of homogeneous Cauchy-type singular integral equations by means of Fourier integral transform. The integral equations are solved numerically by utilizing Gauss-Chebyshev integral formulae. Numerical results for buckling loads are presented for various geometrical parameters and are compared with those obtained from classical theory of beam-plate stability based on the Kirchhoff assumption. The comparison of both results shows that the buckling loads obtained from the classical theory of beam-plate stability are much larger than those obtained from the mathematical theory of elasticity, referring to which the limitations of the classical theory applied to the present buckling problem are discussed. A simple but accurate approximate method for estimating the buckling load is developed by the use of the elastic support coefficient obtained from the present analysis and the Euler formula derived from the classical theory for the case of elastically supported ends. Finally, the numerical results of the buckling wave shapes and the Mode I and II stress factors, which cannot be obtained from the classical theory, are presented.     

Near-tip behavior of a crack in a plane anisotropic elastic body

The asymptotic form of the stress and displacement components near the tip of a straight crack in a generally rectilinear anisotropic plane elastic body are resolved. As in the isotropic analysis, the solutions for the stresses display a $\text{r}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ dependence, where r is the distance from the tip, while the angular dependence depends upon the anisotropy in a complicated way. The effect of some special anisotropies upon these solutions is fully explored. Finally, these solutions are used to solve the problem of a finite length straight crack in an anisotropic elastic plane when uniform stresses are applied far from the crack. This solution includes obtaining the stress intensity factors, and the nature and magnitude of the crack face displacements.     

Mode I crack in a soft ferromagnetic material

ABSTRACT In the existing magnetoelastic theories, stress is proportional to the square of magnetic intensity and the linear model developed is usually used to analyse magnetoelastic problems. For a crack problem, the perturbation of the magnetic field caused by deformation is not much less than the applied field. In this paper, complex potentials for a mode I crack with a nonlinear relation for magnetic intensity are developed. The boundary conditions on crack faces are represented in terms of the continuity of the magnetic field. A solution of the crack problem is obtained by solving the Riemann‐Hilbert problem. Making use of the solution, the effects of the boundary conditions on the crack faces on the magnetoelastic coupling are discussed.     

Thermoelastic wave propagation in an elastic solid containing a finite crack

Investigated in this paper is the scattering of plane harmonic thermoelastic waves around the tip of a finite crack. Integral transform techniques are used to formulate the problem and reduce it to Fredholm integral equations of the second kind. The equations are solved numerically and the singular stress field near the crack tip is determined. In particular, the variation of the stress intensity factor with the frequency of the incoming wave is exhibited graphically. The peak in the magnitude of the stress intensity factor is of paramount interest in the application of fracture mechanics to thermal stress problems.     

Plastic deformation in a thick transversely isotropic layer containing a penny-shaped crack

Summary The width of a thin plastic annular zone formed during the deformation of a pennyshaped crack in a transversely isotropic layer of an ideal elasto-plastic material is determined. Considered are the cases where the penny-shaped crack is extended by normal stresses and by torsional stresses. The faces of the layer are shear free and deformation of the plastic zone around the penny-shaped crack occurs according to the Dugdale hypothesis. For each case, the solution of the problem is reduced to a Fredholm integral equation of the second kind. Iterative solutions are obtained for small values of the parameters and numerical results for the width of the plastic zone are determined. Graphical results showing the effect of transverse isotropy upon the width of the plastic zone are also presented.With 6 Figures