S. Thangjitham

Stress Analysis of Multilayered Anisotropic Elastic Media

The stress analysis of media subjected to applied surface tractions is performed. The solutions are obtained based on the Fouier transfrom technique together with the aid of he stiffness matrix approach. It can be uniformly applied to media with transversely isotropic, orthotropic, and monoclinic layers

Thermal stress singularities in an anisotropic slab containing a crack

Abstract The steady-state thermoelasticity problem of a cracked fiber-reinforced slab under a state of generalized plane deformation is studied. The crack is considered to be located on a plane parallel to the bounding surfaces of the slab. Based on the method of Fourier integral transform, the current mixed boundary value thermoelasticity problem is reduced to solving two sets of singular integral equations for heat conduction and thermal stresses in a cracked anisotropic medium. The thermally-induced crack-tip stress intensity factors are defined in terms of the solutions of the corresponding integral equations. Numerical results are presented, focusing on the effects of relative crack size, crack location, and fiber volume fraction on the thermal stress intensity factors as a function of the fiber orientation angle. The effect of a partially insulated crack surface condition on the strength of thermal stress singularities is also discussed.

THERMAL STRESSES IN CONCENTRIC CYLINDERS DUE TO ASYMMETRIC AND TIME DEPENDENT TEMPERATURE INPUTS

Abstract A frequency domain solution is developed for the boundary-value problem of thermal stresses in concentric layered cylinders due to asymmetric and time dependent temperature inputs. Complex frequency response functions are defined for the temperature and stresses in the wall of a cylindrical body. Numerical results for a system of layered cylinders exposed to solar radiation input are obtained.

Micro- and macromechanical stress and failure analyses of laminated composites

Abstract The micro- and macromechannical responses of laminated composites in regions of high stress gradients are examined within the framework of linear plane elasticity. The micromechanical model is based on a system of alternating layers of heterogeneous reinforcement and matrix, whereas the macromechanical counterpart is characterized by the effective homogeneous, orthotropic properties of the constituents. The Fourier transform and the stiffness matrix formulation are employed. As a numerical illustration, a semi-infinite medium made of aluminum and boron layers subjected to a concentrated load is considered. The micro- and macromechanical stress fields as well as the corresponding failure stresses are presented to measure the degree of correspondence between the two models.

Interlaminar crack problems of a laminated anisotropic medium

Abstract The interlaminar crack problems of a fiber-reinforced composite laminate under a state of generalized plane deformation are studied within the theory of anisotropic elasticity. The crack is considered to be embedded within a matrix interlaminar region of the laminate. Based on the Fourier integral transform technique and the stiffness matrix formulation, the current mixed boundary value problem is reduced to solving a system of Cauchy-type singular integral equations of the first kind. Within the context of linear fracture mechanics, the stress intensity factors are then defined in terms of the solutions of the corresponding integral equations. Numerical results are obtained for in-plane normal (mode I), in-plane shear (mode II), and anti-plane shear (mode III) crack surface loadings. Under each loading, the effects of layer fiber orientation and crack location on both the major and coupling stress intensity factors are illustrated.

Thermally-induced interlaminar crack-tip singularities in laminated anisotropic composites

Thermally-induced stress singularities of an interlaminar crack in a fiber-reinforced composite laminate under a state of generalized plane deformation are examined within the framework of steady-state anisotropic thermoelasticity. The crack is assumed to be embedded within a matrix-rich interlaminar region of the composite. The Fourier integral transform technique and the flexibility/stiffness matrix method are introduced to formulate the current mixed boundary value problem. As a result, two sets of simultaneous Cauchy-type singular integral equations of the first kind are derived for the heat conduction and thermoelasticity. Within the context of linear elastic fracture mechanics, the mixed-mode thermal stress intensity factors are defined in terms of the solutions of the corresponding integral equations. Numerical results are presented, addressing the effects of laminate stacking sequence, crack location, and crack surface partial insulation on the values of thermal stress intensity factors.

THERMALLY INDUCED LOCAL EFFECTS IN LAMINATED COMPOSITES

The steady-state thermally induced local effects in laminated composite materials are investigated from the micro- and macromechanical points of view. The micro-mechanical model is represented by the alternating layers of a perfectly bonded matrix-reinforcement system while the macromechanical counterpart is characterized by the effective thermal and mechanical properties of the constituent layers. The solutions are obtained within the framework of linear plane thermoelasticity via the Fourier transform technique and the flexibility/stiffness matrix method. As a numerical illustration, the micro- and macromechanical temperature and thermal stress fields due to given surface temperature distributions are presented to measure the degree of correspondence between the two models. Considerable discrepancies are observed to exist between the micro- and macromechanical thermal stress fields, especially, in regions involving high temperature gradients.

The interlaminar crack-tip response in a fiber-reinforced composite laminate

A solution is presented for the problem of an interlaminar crack in a laminated fiber-reinforced composite material. The theory of anisotropic elasticity under a state of generalized plane deformation is employed as a basic framework of this study. In the analytical model, dissimilar anisotropic half-spaces with different fiber orientations which are bound together by a matrix interlayer are considered. The interlayer approximates the matrix-rich interlaminar region containing the crack. The stiffness matrix approach is utilized and the current crack problem is reduced to solving a system of singular integral equations. The singular response of an interlaminar crack to in-plane normal, in-plane shear, and anti-plane shear loadings is evaluated in terms of mixed-mode stress intensity factors. Under each of the leading conditions, the parametric effects of laminate stacking sequence, relative crack size, crack location, and fiber volume fraction are addressed.

Singular crack-tip response in an anisotropic medium

Abstract The stress analysis of a cracked fiber-reinforced slab under the state of generalized plane deformation is performed within the framework of linear anisotropic elasticity. The crack is located parallel to the bounding surfaces of the slab. The crack-tip stress intensity factors are defined in terms of the solution of the system of singular integral equations of the first kind. Numerical results are provided, illustrating the singular crack-tip response to in-plane normal, in-plane shear, and anti-plane shear loading conditions. Under each applied loading, the effects of relative crack size, crack location, and fiber volume fraction on the values of stress intensity factors are addressed for a given range of fiber orientations.

Heat conduction in laminated anisotropic composites with a debonding

Abstract The plane problem of steady-state heat conduction in a laminated anisotropic slab containing an interfacial debonding is considered. The arbitrary temperature distribution is assumed to be prescribed on the bounding planes of the slab while the heat flux is specified on the debonding surfaces. The flexibility matrix approach is introduced to formulate the current mixed boundary value problem for the multilayered medium. A singular integral equation of the first kind is then obtained for the problem. As an illustrative example, temperature distributions in a laminated slab resulting from a uniform temperature rise on the bounding planes and the completely insulated debonding surfaces are presented. Temperature discontinuities across the debonding surfaces are obtained as functions of the ratio of thermal conductivity coefficients, the direction of anisotropy, and the debonding locations.