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.

Personal Reflections of My Research in Structural Mechanics: Past, Present, and Future

Abstract: The personal reflections of the author’s research in structural mechanics, covering the development of shear deformation theories of laminated composite plates and shells (past and present), and formulation of nonlocal theories (present), and the modelling of web core sandwich and architected materials (present and future) are presented. Various professional milestones are reviewed and the salient features are highlighted. The milestones include: (1) Reddy’s third-order shear deformation laminate plate theory for quadratic representation of the interlaminar shear stresses without the use of shear correction factors, (2) Reddy’s layerwise theory for laminates for accurate determination of interlaminar stresses, (3) algebraic relationships between the bending solutions of shear deformation theories and classical theories of beams and plates, (4) locking-free shell finite elements accounting for thickness stretch, (5) strain gradient/modified couple stress theories for beams and plates, and (6) nonlocal micropolar theory of plates to model web core structures. Due to the space limitations, a discussion of only topics 5 and 6 are included here.

Modeling impact fracture in a quasi-brittle solids using a 3D nonlocal graph-based finite element analysis: Theory, finite element simulations, and experimental verification

Abstract: In this work, the authors have developed and implemented a novel nonlocal three-dimensional graph-based finite element approach for simulating fracture in quasi-brittle solids as an extension of their previous work in two dimensions. In order to validate the nonlocal aspects of the model, the authors have also fabricated a gypsum-based particulate composite with silica particles of specific dimensions and mass fractions, thus the length scale of the material is fixed by the particulate media. The GraFEA fracture model is implemented in a graphics processing unit (GPU) parallel computing environment that allows substantial speed-up of the simulations in both cases of impact and quasi-static loading conditions. The improvement in computational performance is especially essential for carrying out the simulation of parametric study. Comparison of the physical response of this specially designed composite with the three-dimensional nonlocal GraFEA shows that the model is capable of simulating fracture in such materials. Finally, the efficacy of simulating impact response of concrete including crack closure behavior is tested by simulating hammer drop test for the concrete beam sample and cyclic shear loading on the circumferentially-notched concrete cylinder sample. • Formulation of a three-dimensional nonlocal graph-based finite element approach for fracture. • GPU parallelized implementation of the three-dimensional GraFEA theory as an ABAQUS VUMAT subroutine. • Independent prediction of low-speed impact fracture of specially fabricated gypsum-based particulate composite to validate the nonlocal fracture length scale. • Simulation of concrete hammer drop impact test and cyclic shear loading with crack closure to validate the efficacy of the developed model.

Restrictions on the Material Coefficients in the Constitutive Theories for Non-Classical Viscous Fluent Continua

Abstract: This paper considers conservation and balance laws and the constitutive theories for non-classical viscous fluent continua without memory, in which internal rotation rates due to the velocity gradient tensor are incorporated in the thermodynamic framework. The constitutive theories for the deviatoric part of the symmetric Cauchy stress tensor and the Cauchy moment tensor are derived based on integrity. The constitutive theories for the Cauchy moment tensor are considered when the balance of moments of moments 1) is not a balance law and 2) is a balance law. The constitutive theory for heat vector based on integrity is also considered. Restrictions on the material coefficients in the constitutive theories for the stress tensor, moment tensor, and heat vector are established using the conditions resulting from the entropy inequality, keeping in mind that the constitutive theories derived here based on integrity are in fact nonlinear constitutive theories. It is shown that in the case of the simplest linear constitutive theory for stress tensor used predominantly for compressible viscous fluids, Stokes' hypothesis or Stokes' assumption has no thermodynamic basis, hence may be viewed incorrect. Thermodynamically consistent derivations of the restrictions on various material coefficients are presented for non-classical as well as classical theories that are applicable to nonlinear constitutive theories, which are inevitable if the constitutive theories are derived based on integrity.

Thermoviscoplasticity in Body-Centered Cubic Metals: A Two-Temperature Model With Grain Boundary Evolution

Abstract: In this work, we develop a thermo-viscoplasticity model for body-centered cubic (BCC) metals based on a two-temperature theory of nonequilibrium thermodynamics. Modeling the plastic deformation here involves two subsystems, viz., a configurational subsystem related to grain growth, dislocation motion, and a kinetic vibrational subsystem describing the vibration of atoms. Due to a separation of the time scales, the two subsystems are described by two different temperatures. In this study, we introduce a grain boundary density, in addition to the mobile and forest dislocation densities, as an internal variable. The focus in this paper is on how large plastic deformation is affected by the evolving grain boundaries. In order to check the predictive quality of the model, numerical simulations are conducted and validated against available experimental evidence wherever possible.

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.