J. N. Reddy

Bio: J. N. Reddy is an academic researcher from Texas A&M University. The author has contributed to research in topics: Finite element method & Plate theory. The author has an hindex of 106, co-authored 926 publications receiving 66940 citations. Previous affiliations of J. N. Reddy include Instituto Superior Técnico & National University of Singapore.

Multiscale modeling of strength and failure behavior of carbon nanostructure reinforced epoxy composite adhesives in bonded systems

Abstract: In this study, atomistic based continuum (ABC) multiscale modeling approach is presented for strength and failure prediction of carbon nanotube (CNT) reinforced epoxy composite adhesives in bonded systems. Assuming that the CNTs are uniformly dispersed in the epoxy matrix , the mechanical properties of the nanocomposite adhesive are determined utilizing a two-step sequential homogenization procedure. In the first step, effective mechanical properties of a nanoscale representative volume element (RVE) are determined. The RVE comprises a CNT embedded in the epoxy matrix separated by an interphase . The structure-property relationship at the nanoscale is captured through ABC modeling approach wherein a CNT is modeled as a space-frame structure with beam elements and the epoxy is modeled using solid elements. The interphase between the CNT and the epoxy is modeled using non-linear spring elements to account for non-bonded van-der Waals interactions. In the second step, CNT inclusions with random orientations in the matrix are considered to create a microscale RVE of the nanocomposite. In both the steps, different boundary conditions were applied on the RVEs, and finite element (FE) analyses were conducted to estimate the effective mechanical properties through numerical homogenization. Furthermore, the strength of CNT/epoxy composite is estimated using modified Kelly-Tyson theory. Finally, modeling scheme proposed here is utilized to assess the load carrying capacity and failure behavior of a single lap-joint (SLJ) comprising composite adherends and CNT/epoxy nanocomposite adhesive by conducting continuum scale FE analyses. Results show over 30% improvement in strength for the SLJ with CNT/epoxy bondlayer comprising 2 vol% CNT. The findings of the study indicate that both strength and damage tolerance of the bonded joints can be significantly optimized utilizing nanoreinforced bondlayer.

Thermodynamic consistency of beam theories in the context of classical and non-classical continuum mechanics and a thermodynamically consistent new formulation

Abstract: In order to enhance currently used beam theories in $$\mathbb {R}^2$$ and $$\mathbb {R}^3$$ to include mechanisms of dissipation and memory, it is necessary to establish if the mathematical models for these theories can be derived using the conservation and the balance laws of continuum mechanics in conjunction with the corresponding kinematic assumptions. This is referred to as thermodynamic consistency of the beam mathematical models. Thermodynamic consistency of the currently used beam models will permit use of entropy inequality to establish constitutive theories in the presence of dissipation and memory mechanism in the currently used beam theories. This is the main motivation for the work presented in this paper. The currently used beam theories are derived based on kinematic assumptions related to the axial and transverse displacement fields. These are then used to derive strain measures followed by constitutive relations. For linear beam theories, strain measures are linear functions of displacement gradients and stresses are linear functions of strain measures. Using these stress and strain measures, energy functional is constructed over the volume of the beam consisting of kinetic energy, strain energy and potential energy of loads. The Euler’s equation(s) extracted from the first variation of this energy functional set to zero yields the differential equations describing the evolution of the deforming beam. Alternatively, principle of virtual work can also be used to derive mathematical models for beams. For linear elastic behavior with small deformation and small strain, the two approaches yield same mathematical models. In this paper we examine whether the currently used beam mathematical models with the corresponding kinematic assumption (i) can be derived using the conservation and balance laws of classical continuum mechanics or (ii) are the conservation and balance laws of non-classical continuum mechanics necessary in their derivation. In order to ensure that the mathematical models for various beam theories result in deformation that is in thermodynamic equilibrium we must establish the consistency of the beam theories with regard to the conservation and the balance laws of continuum mechanics, classical or non-classical in conjunction with their corresponding kinematic assumptions. Currently used Euler–Bernoulli and Timoshenko beam mathematical models that are representative of most beam mathematical models are investigated. This is followed by details of general and higher-order thermodynamically consistent beam theory that is free of kinematic assumptions and other approximations and remains valid for slender as well as deep beams. Model problem studies are presented for slender as well as deep beams. The new formulation presented in this paper ensures thermodynamic equilibrium as it is derived using the conservation and the balance laws of continuum mechanics and remains valid for slender as well as non-slender beams.

Study of the effect of embedded piezoelectric layers in composite cylinders

Abstract: An elasticity solution is presented for the static equilibrium equations of an axisymmetriccomposite cylinder under loadings due to surface mounted or embedded piezoelectric laminae.Both uniform and non—uniform distributions of the piezoelectric effect are studied and results areverified using a finite element analysis based on axisymmetric 2—D elasticity theory equations. Acylindrical 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 thepatch. 1. INTRODUCTION One of the most recent advancements in the field of piezoelectricity is the discovery of thepiezoelectric effect in a polymer based material called polyvinylidene fluoride (PVDF)' . Compared to other materials, PVDF is flexible, rugged, available in thin sheets and easily manufactured inlarge quantities and at a low cost2. For these reasons, PVDF is currently being studied for useas distributed sensors/actuators in flexible structures. However, before piezoelectric materials canbe successfully used for control, the mechanical interaction between them and the structure beingcontrolled must be well understood.In this paper, two analytical tools are used to study the effects of embedded PVDF laminae inan axisymmetric composite cylinder. An elasticity solution is presented for the static equilibriumequations and verified using the finite element method. These tools are used to develop a cylindrical

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Robot dynamics and control

Abstract: From the Publisher: This self-contained introduction to practical robot kinematics and dynamics includes a comprehensive treatment of robot control. Provides background material on terminology and linear transformations, followed by coverage of kinematics and inverse kinematics, dynamics, manipulator control, robust control, force control, use of feedback in nonlinear systems, and adaptive control. Each topic is supported by examples of specific applications. Derivations and proofs are included in many cases. Includes many worked examples, examples illustrating all aspects of the theory, and problems.

A Simple Higher-Order Theory for Laminated Composite Plates

Abstract: A higher-order shear deformation theory of laminated composite plates is developed. The theory contains the same dependent unknowns as in the first-order shear deformation theory of Whitney and Pagano (1970), but accounts for parabolic distribution of the transverse shear strains through the thickness of the plate. Exact closed-form solutions of symmetric cross-ply laminates are obtained and the results are compared with three-dimensional elasticity solutions and first-order shear deformation theory solutions. The present theory predicts the deflections and stresses more accurately when compared to the first-order theory.