JN Reddy | Texas A&M University at Qatar (original) (raw)

Papers by JN Reddy

Materials Science and Technology, 2013

ABSTRACT A creep damage model from the micromechanics viewpoint is presented in the paper. In ord... more ABSTRACT A creep damage model from the micromechanics viewpoint is presented in the paper. In order to mitigate the difficulty of calibrating many parameters in the existing damage evolution models, a simple creep ductility exhaustion approach is employed to account for the accumulation of the creep damage. Two-dimensional and three-dimensional numerical analyses of creep crack growth based on the new creep-damage model and/or Liu-Murakami model are carried out. When the damage parameter reaches a critical value, the load carrying capacity of each damaged element approaches zero and thus crack growth can be characterised by a completely damaged element zone ahead of the initial crack tip. The finite element simulation results obtained are compared favourably with experimental data for the compact tension specimen for 316 stainless steel and bending cracked plate for T91 steel at elevated temperatures. The comparisons show the excellent capability of the proposed model in predicting the crack growth rate and progressive crack profiles. In addition, the influences of the plasticity and mesh size are discussed in this paper.

$Research paper thumbnail of The Jacobian derivative method for three-dimensional fracture mechanics$

Communications in Applied Numerical Methods, 1990

This paper presents a new algorithm to compute the distribution of the strain energy release rate... more This paper presents a new algorithm to compute the distribution of the strain energy release rate along the crack front for three-dimensional cracks (e.g surface cracks). The algorithm is economical and accurate. The algorithm is illustrated via two-dimensional and three-dimensional examples including a surface crack in a cylinder under internal 'pressure and sieJe-grooved compact-test specimens. It is shown, via specific examples, that only a single, self-similar virtual crack extension is necessary to accurately compute the strain-energy release-rate distribution along the crackfront.

Annals of Solid and Structural Mechanics, 2009

In a series of papers and a book the author and his colleagues have developed algebraic relations... more In a series of papers and a book the author and his colleagues have developed algebraic relationships between the solutions (e.g., deflections, buckling loads, and frequencies) of a given shear deformation theory of beams or plates and the corresponding classical theory solutions. The bending relationships, for example, can be used to generate the generalized displacements and forces according to the particular shear deformation theory from the known generalized displacements and forces of the same problem according to the classical theory. In the present study relationships between the bending solutions of several shear deformation beam and plate theories and the classical beam and plate theories are presented in a canonical form, i.e., one set of relationships contains several theories and they can be specialized to a specific theory by assigning values to the parameters appearing in the relationships. Numerical examples of bending solutions for beams and rectangular plates with various boundary conditions are presented to show how the relations can be used to determine the deflections, bending moments, and shear forces for various theories. The relationships are validated by comparing the numerical results obtained using the relationships for the first-order plate theory against analytical solutions or those computed using the ABAQUS finite element program.

Journal of Applied Mechanics, 1995

A power series solution is presented for the static equilibrium equations of an axisymmetric comp... more A power series solution is presented for the static equilibrium equations of an axisymmetric composite cylinder under loadings due to surface mounted or embedded piezoelectric laminae. Both uniform and nonuniform distributions of the piezoelectric effect are studied and results are verified using a finite element model based on axisymmetric two-dimensional elasticity theory equations. A cylindrical truss element actuator is developed which may be used for damping vibrations of truss-type structures. Finally, the effects of a piezoelectric patch have been investigated. The axial forces generated at the fixed ends of a cylinder are found to be proportional to the length of the patch.

Low Frequency Noise, Vibration and Active Control, 2015

The purpose of the present work is to theoretically investigate the active control of radiated so... more The purpose of the present work is to theoretically investigate the active control of radiated sound power from a simply supported soft-core sandwich panel with a line moment excitation. Since noise transmission in the low frequency region through a soft-core sandwich panel mainly occurs due to flexural and dilatational modes, therefore, the focus of this study is to control these modes and achieve sound attenuation in a large frequency band. Two control methods, volume velocity and weighted sum of spatial gradients (WSSG) are used to drive three piezoelectric actuators (PZTs) attached on the exterior side of the bottom face plate. The governing equation of the sandwich panel with the PZTs is derived using the Hamilton's principle considering Reddy's third order shear deformation theory. Numerical studies indicate that while the line moment is at the mid vertical line, WSSG is able to attenuate the radiated sound power irrespective of core loss factor whereas volume velocity could not. However, both the control metrics are able to attenuate most of the structural modes, when the line moment is off the midline, and therefore, attenuate significant amount of radiated sound power in a broad frequency range. And the maximum increase in sound power is small in WSSG as compared to volume velocity. These results show that WSSG can be used as an effective control metric to mitigate low frequency sound.

The paper presents numerical results obtained by a penalty finite element model for natural conve... more The paper presents numerical results obtained by a penalty finite element model for natural convection between concentric horizontal cylinders in the presence of temperature gradient between the inner and outer cylinders. The results are compared with experimental results as well as other approximate solutions for moderately high Rayleigh numbers, R sub A. The agreement is found to be very good.

A probabilistic micromechanics-based nonlinear analysis procedure is developed to predict and qua... more A probabilistic micromechanics-based nonlinear analysis procedure is developed to predict and quantify the variability in the properties of high temperature metal matrix composites. Monte Carlo simulation is used to model the probabilistic distributions of the constituent level properties including fiber, matrix, and interphase properties, volume and void ratios, strengths, fiber misalignment, and nonlinear empirical parameters. The procedure predicts the resultant ply properties and quantifies their statistical scatter. Graphite copper and Silicon Carbide Titanlum Aluminide (SCS-6 TI15) unidirectional plies are considered to demonstrate the predictive capabilities. The procedure is believed to have a high potential for use in material characterization and selection to precede and assist in experimental studies of new high temperature metal matrix composites.

International Journal of Solids and Structures, 2007

A geometrically nonlinear analysis of functionally graded shells is presented. The two-constituen... more A geometrically nonlinear analysis of functionally graded shells is presented. The two-constituent functionally graded shell consists of ceramic and metal that are graded through the thickness, from one surface of the shell to the other. A tensor-based finite element formulation with curvilinear coordinates and first-order shear deformation theory are used to develop the functionally graded shell finite element. The first-order shell theory consists of seven parameters and exact nonlinear deformations and under the framework of the Lagrangian description. High-order Lagrangian interpolation functions are used to approximate the field variables to avoid membrane, shear, and thickness locking. Numerical results obtained using the present shell element for typical benchmark problem geometries with functionally graded material compositions are presented.

IUTAM Symposium on Multi-Functional Material Structures and Systems, 2009

ABSTRACT The material properties of biological materials, often derived from experiments, are fou... more ABSTRACT The material properties of biological materials, often derived from experiments, are found to vary by orders of magnitude. This disparity in experimentally-derived mechanical properties can be understood only by mathematical models that correlate the structural constituents to its mechanical response. New mechano-biological computational models that consider the effect of microstructural constituents on the response of biological materials are considered in this paper. Various mathematical models are presented to study the macroscopic effects, such as deformation and diffusion in tissues, using multi-scale computational models. The implementation of the computational models for the determination of mechanical behaviour in pathological conditions like cancer progression, cardiovascular diseases, and gynaecological conditions are discussed. The significance of this work lies in the use of a multi-physical modelling of the complex material geometry as well as physical processes representing physiological systems, thereby establishing a suitable and efficient multi-scale computational framework. KeywordsBio-materials-Biphasic finite elements-Micromechanics-Soft tissue

Smart Materials and Structures, 2004

Third-order shear deformation theories of laminated composite shells are developed using the stra... more Third-order shear deformation theories of laminated composite shells are developed using the strain-displacement relations of Donnell and Sanders theories. These theories also account for geometric nonlinearity in the von Kármán sense. Analytical (Navier) solutions for vibration suppression in cross-ply laminated composite shells with surface mounted smart material layers are developed using the linear versions of the two shell theories and for simply supported boundary conditions. Numerical results are presented to bring out the parametric effects of shell types (cylindrical, spherical, and doubly curved shells) and material properties on vibration suppression. A simple negative velocity feedback control in a closed loop is used.

Smart Materials and Structures, 2003

... Optimal placements of the patches are determined by employing a modal controllability criteri... more ... Optimal placements of the patches are determined by employing a modal controllability criterion to control the first two modes of vibration. ... The development of high performance lightweight structures must consider the incorporation of an active control mechanism to ...

Sadhana, 1994

The layerwise theory of Reddy is used to study the low velocity

Metallurgical Transactions B, 1993

A finite element model for the solidification of molten metals and alloys in cylindrical molds is... more A finite element model for the solidification of molten metals and alloys in cylindrical molds is developed using the energy equation in terms of temperature and enthalpy. The Newton-Raphson technique was used to solve the resulting nonlinear algebraic equations. A computer program is developed to calculate the enthalpy, temperature, and fraction solid per the classical Lever rule, Scheile equation, and Brody-Flemings models. Cooling curves are calculated for pure metal (aluminum), two eutectic alloys (A1-33.2 pct Cu and A1-12.6 pct Si), and three hypoeutectic alloys (A1-2.2 pct Cu, A1-4.5 pct Cu and AI-7 pct Si) and are compared with the experimental curves.

Mechanics of Advanced Materials and Structures, 2010

This paper presents development of mathematical models for multi-physics interaction processes in... more This paper presents development of mathematical models for multi-physics interaction processes in which the physics of solids, liquids and gases are described using conservation laws, appropriate constitutive equations and equations of state in Eulerian description. The use of conservation laws in Eulerian description for all media of an interaction process and the choice of the same dependent variables in the resulting governing differential equations (GDEs) for solids, liquids and gases ensure that their ...

Mathematics of Computation, 1995

Journal of the Mechanics and Physics of Solids, 2008

... Eq. (20) vanishes for the beam whose configurations at t=0 and T are prescribed. Then, using ... more ... Eq. (20) vanishes for the beam whose configurations at t=0 and T are prescribed. Then, using the fundamental lemma of the calculus of variation (eg, Gao and Mall, 2001; Reddy, 2007a; Gao and Park, 2007) in Eq. (20) yields ...

Journal of Sound and Vibration, 2003

Journal of Polymer Science Part B: Polymer Physics, 2007

ABSTRACT Parametric studies were performed using finite element analysis (FEA) to learn how mater... more ABSTRACT Parametric studies were performed using finite element analysis (FEA) to learn how material and surface properties of polypropylene (PP) affect scratch behavior. Three-dimensional FEA modeling of scratching on a PP substrate with a spherical-tipped indenter is presented. Three different loading conditions, that is constant scratch depth, constant normal load, and linearly increasing normal load, are adopted for this parametric study. From the FEA findings, it is learned that Poisson&#39;s ratio has a negligible effect on scratch performance, whereas raising the coefficient of adhesive friction induces a significantly larger residual scratch depth and tangential force on the scratch tip. Increasing the Young&#39;s modulus of a material does not necessarily improve its overall scratch performance. On the other hand, modifying the yield stress of a material has a major impact on scratch resistance as a higher yield stress reduces the residual scratch depth. From this numerical effort, it is concluded that the yield stress and coefficient of adhesive friction are the most critical parameters to influence the scratch performance of a material. Analyses also suggest that the general trend in the parametric effect of the above four parameters on scratch behavior is independent of the applied normal load level. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1435–1447, 2007

Journal of Intelligent Material Systems and Structures, 1997

A study on the effective thermomechanical response of a composite laminate with shape memory allo... more A study on the effective thermomechanical response of a composite laminate with shape memory alloy (SMA) layers based on the implementation of the layerwise laminate theory in the finite element method is carried out in this paper. The SMA thermomechanical constitutive response is based on a thermomechanical model recently developed by Boyd and Lagoudas. The numerical implementation of the constitutive model is based on a return mapping integration algorithm which is employed in studying the SMA response characteristics in the composite laminate under thermal loading. In modeling the laminate, a displacement based finite element approach is used in conjunction with the layerwise laminate theory of Reddy, incorporating piecewise continuous distribution of transverse strains through the thickness. As an illustrative example, the deformations caused by two prestrained SMA strips placed symmetric to the mid-plane of an elastic plate, when thermally activated are studied. The top SMA str...

Journal of Elasticity, 1995

A hybrid method is presented for the analysis of layers, plates, and multilayered systems consist... more A hybrid method is presented for the analysis of layers, plates, and multilayered systems consisting of isotropic and linear elastic materials, The problem is formulated for the general case of a multilayered system using a total potential energy formulation. The layerwise laminate theory of Reddy is employed to develop a layerwise, two-dimensional, displacement-based, hybrid boundary element model that assumes piecewise continuous distribution of the displacement components through the system's thickness. A one-dimensional finite element model is used for the analysis of the multilayered system through its thickness, and integral Fourier transforms are used to obtain the exact solution for the in-plane problem. Explicit expressions are obtained for the fundamental solution of a typical infinite layer (element) assuming linear displacement distribution through its thickness. This fundamental solution is given in a closed form in the cartesian space, and it can be applied in the two-dimensional boundary integral equation model to analyze layered structures with finite dimensions. The proposed method provides a simple, efficient, and versatile model for a three-dimensional analysis of thick plates or multilayered systems.