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.

A Phase-Field Damage Model for Orthotropic Materials and Delamination in Composites

Abstract: A phase-field damage model for orthotropic materials is proposed and used to simulate delamination of orthotropic laminated composites. Using the deviatoric and hydrostatic tensile components of the stress tensor for elastic orthotropic materials, a degraded elastic free energy that can accommodate damage is derived. The governing equations follow from the principle of virtual power and the resulting damage model, by its construction, conforms with the physical relevant condition of no matter interpenetration along the crack faces. The model also dispenses with the traction separation law, an extraneous hypothesis conventionally brought in to model the interlaminar zones. The model is assessed through numerical simulations on delaminations in mode I, mode II, and another such problem with multiple initial notches. The present method is able to reproduce nearly all the features of the experimental load displacement curves, allowing only for small deviations in the softening regime. Numerical results also show forth a superior performance of the proposed method over existing approaches based on a cohesive law.

Transient Response of Laminated, Bimodular-Material, Composite Rectangular Plates

Abstract: The paper presents a finite-element analysis of the transient behavior of fiber-reinforced, single-layer and two-layer cross-ply rectangular plates of bimodular materials (i.e., materials whose linear elastic properties are dif ferent depending on whether the fiber-direction strains are tensile or com pressive). To validate the finite element results, a closed-form solution is also presented for a rectangular plate with all edges simply-supported without in- plane restraint (along the edge) and tangential rotation and subjected to sud denly applied sinusoidally distributed normal pressure. The time behavior of the transverse loading is arbitrary (e.g., step loading, impulse loading, etc.). Numerical results for transverse deflection and locations of the 'neutral sur face' as functions of time are presented for two bimodular materials. The finite element solutions agree very closely with the closed-form solutions.

GraFEA: a graph-based finite element approach for the study of damage and fracture in brittle materials

Abstract: In this paper the conventional finite element method for linear elastic response is reformulated in such a way that makes it favorable for the study of damage and fracture in brittle materials This modified finite element framework is based on the idea presented by Reddy and Srinivasa (Finite Elem Anal Des 104:35–40, 2015), where it was shown that for discretized hyperelastic materials, the magnitude of the nodal forces (in the discretized form) can be written in terms of the axial strains along the edges of the elements and that the equilibrium equations at each node can be written in terms of the forces along the edges alone Using this concept and by exploiting the fact that FEM discretization leads to an undirected cyclic graph with nodes and edges whose connectivity is related to the elements of the FEM, one can reformulate the displacement-based finite element framework with constant strain triangular elements to represent the continuum as a nonlocal network The network representation of the continuum is “nonlocal” in the sense that the force along any given edge doesn’t only depend on the strain along that edge, but on a collective behavior of the strains along the edges neighboring the edge of interest This method is named as GraFEA (for graph-based finite element analysis) Damage is introduced using a nonlocal damage criterion originating from the idea of the weakest links statistics proposed by Lin, Evans, and Ritchie (J Mech Phys Solids 34(5):477–497, 1986) This idea, which was very successful in studying cleavage fracture of mild steel at very low temperatures, can be used to impose a damage criterion to the nolocal network GraFEA has the major advantage that one can impose an edge-based failure criterion using the weakest link thoery directly on the discretized body, and potentially simulating crack initiation, crack growth, and branching without the need for extra enrichment functions (as with other methods) The simplicity of the method and the fact that it is based on conventional finite element method makes it suitable for integration into commercial softwares The governing equations for this approach are derived and applied to two simple crack growth simulations (as a proof of concept) in two-dimensional regions with a hole

New model for creep damage analysis and its application to creep crack growth simulations

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 an...

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.