StructuResearch Group

United Kingdom

StructuResearch Group

United Kingdom
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Subba Rao P.,StructuResearch Group | Subba Rao P.,Indian Institute of Science | Renji K.,StructuResearch Group | Bhat M.R.,Indian Institute of Science
Journal of Reinforced Plastics and Composites | Year: 2017

This paper presents molecular dynamics (MD) simulations on the effects of carbon nanotubes (CNTs) without and with chemical functionalization, on the mechanical properties of bisphenol E cyanate ester (BECy) - a potential structural resin. Atomistic models of CNTs, functionalized CNTs (fCNTs), BECy resin, CNT-BECy and fCNT-BECy resins with definite quantity of CNT/fCNT are built. Using these atomistic models, mechanical properties of the above nanosystems are estimated through a computational method involving geometric optimization and equilibration through MD by judiciously establishing various parameters. Adoptability of the approach taken up in this work to model and solve complex nanosystems capturing interactions in the interfacial region between CNT/fCNT and the resin to understand the mechanical behaviour has been highlighted. These investigations have yielded interesting and encouraging results to arrive at optimum quantity of CNTs/fCNTs to be added to achieve enhanced mechanical properties of BECy resin that validate the previous experimental studies carried out by the authors infusing similar quantities of CNTs and fCNTs into BECy. © The Author(s) 2016.

Sekhar B.R.,Indian Institute of Science | Gopalakrishnan S.,Indian Institute of Science | Murthy M.V.V.S.,StructuResearch Group
Procedia Engineering | Year: 2017

A spectral element formulation is developed for a sandwich beam with stiff face sheets and a compliant core. Higher order displacement functions are taken for the core in order to incorporate the core compression effects. Highly efficient spectral element method is used for the study. Accuracy and the computational efficiency of this method are compared with the conventional finite element method in solving transient blast loading case. Using this spectral element method, under water blast loading response of a sandwich beam with composite face sheets and core is studied. A comparison is made between the response of stiff core and compliant core sandwich beam models. The study presents a design approach for an optimal configuration for under water blast resistant structures. © 2017 The Authors.

Raja Sekhar B.,Indian Institute of Science | Gopalakrishnan S.,Indian Institute of Science | Murthy M.V.V.S.,StructuResearch Group
Journal of Sandwich Structures and Materials | Year: 2017

A new time-domain spectral element with nine degrees of freedom per node is formulated based on higher-order sandwich panel theory, incorporating the flexible behaviour of the core with composite face sheets. Static, free vibrations and wave propagation analysis are carried out using the formulated element. Results obtained using this element are compared with those available in the literature and with commercial finite element codes. The fast convergence of the spectral element method is demonstrated by solving the high-frequency wave propagation problem. A method of computing the wave characteristics, namely wavenumbers and group velocities, in a higher-order sandwich panel is developed using the formulated element. The effect of core damping is studied in detail with different core types, which can be used effectively in sandwich beam design. © 2016, © The Author(s) 2016.

Renji K.,StructuResearch Group | Josephine Kelvina Florence S.,StructuResearch Group
Journal of Sound and Vibration | Year: 2017

For the structural design of composite panels, subjected to acoustic excitation, the strains / stresses developed in the panel need to be estimated. In this work expressions for determining the strains / stresses in an SEA framework are derived. A typical composite panel used in spacecraft is subjected to diffuse field acoustic excitation in a reverberation chamber and the accelerations and the strains are measured. The strains are theoretically estimated using the expression derived and they match very well with the measured results. © 2017 Elsevier Ltd

Gupta A.K.,StructuResearch Group | Patel B.P.,Indian Institute of Technology Delhi | Nath Y.,University of Toronto
European Journal of Mechanics, A/Solids | Year: 2015

Abstract The objective of this paper is to investigate the progressive failure behaviour of laminated cylindrical/conical panels under meridional compression considering geometric nonlinearity and evolving material damage. The evolving microscopic damage such as fiber breakage, matrix cracking, fiber matrix debonding etc. is modeled through a generalized macroscopic continuum theory within the framework of irreversible thermodynamics. The analysis is carried out using field consistent finite element approach based on first-order shear deformation theory. The nonlinear governing equations are solved using the Newton-Raphson iterative technique coupled with the adaptive displacement control method to trace the equilibrium path. The damage evolution equations are solved at every Gauss point using Newton-Raphson iterative technique within each iteration of a loading/displacement increment. To accurately model the transverse shear strain energy, shear correction factors are calculated using layers' properties and lamination scheme. The detailed study is carried out to highlight the influences of evolving damage, span-to-thickness ratio, lamination scheme, radius-to-span ratio, boundary conditions and semi-cone angle on the postbuckling response and failure load of laminated panels. © 2015 Elsevier Masson SAS.

Li G.,StructuResearch Group
Journal of Mechanics of Materials and Structures | Year: 2012

In this paper, closed-form solutions for the adhesive stresses in bonded composite single-strap butt joints have been obtained. Two strategies were used for deriving the adhesive peel stress. The solutions are applicable to a butt joint made from different adherend and doubler laminates, as well as the unbalanced single-lap joints. In addition, three-dimensional finite element models of the unit-width composite joints were created for analyzing the adhesive stresses under a plane strain condition. A total of six joint conditions, three joint configurations and each with two layup sequences, were studied. Consistency in the peel stress predictions was obtained from the two theoretical strategies. Good agreement has been achieved between the theoretical and finite element results. The effects of the doubler thickness and laminate layup sequence on the adhesive stress variation can be displayed. The theoretical solution would provide a solid foundation for supporting the practical composite joint assessment. © 2012 by Mathematical Sciences Publishers.

Sairajan K.K.,StructuResearch Group | Nair P.S.,Satellite Center
Composites Part B: Engineering | Year: 2011

Reduction of spacecraft structure mass is an important design goal as it helps to increase the payload fraction, improve agility and also reduce launch cost. The spacecraft is subjected to mechanical loads during launch and thermal loads during on orbit operations. A typical spacecraft contains a main load bearing base structure, which supports all primary payloads and connects the satellite with the launch vehicle. The dimensional stability and tolerance requirements of the payload interfaces are very stringent and there is a need to improve these under the specified thermal environment. This paper explains a novel design consisting of a bonded assembly of metal and laminated composites to achieve a dimensionally stable, low mass base structure without altering the interfaces and overall dynamic behavior of the spacecraft. The design was checked for its performance under all critical loading conditions and was found to meet all requirements including stiffness and stability. Thermal distortion analysis showed that radial distortion is an order of magnitude lower than that of the existing design. The structure was fabricated and it showed compliance to dimensional accuracy requirements. The new base structure weighed 7.54 kg achieving a mass saving of 35% on the existing structure. © 2010 Elsevier Ltd. All rights reserved.

Murthy M.V.V.S.,StructuResearch Group | Renji K.,StructuResearch Group | Gopalakrishnan S.,Indian Institute of Science
Composite Structures | Year: 2015

Spectral elements are found to be extremely resourceful to study the wave propagation characteristics of structures at high frequencies. Most of the aerospace structures use honeycomb sandwich constructions. The existing spectral elements use single layer theories for a sandwich construction wherein the two face sheets vibrate together and this model is sufficient for low frequency excitations. At high frequencies, the two face sheets vibrate independently. The Extended Higher order SAndwich Plate theory (EHSaPT) is suitable for representing the independent motion of the face sheets. A 1D spectral element based on EHSaPT is developed in this work. The wave number and the wave speed characteristics are obtained using the developed spectral element. It is shown that the developed spectral element is capable of representing independent wave motions of the face sheets. The propagation speeds of a high frequency modulated pulse in the face sheets and the core of a honeycomb sandwich are demonstrated. Responses of a typical honeycomb sandwich beam to high frequency shock loads are obtained using the developed spectral element and the response match very well with the finite element results. It is shown that the developed spectral element is able to represent the flexibility of the core resulting into independent wave motions in the face sheets, for which a finite element method needs huge degrees of freedom. © 2015 Published by Elsevier Ltd.

Peereswara Rao M.V.,StructuResearch Group | Harursampath D.,Indian Institute of Science | Renji K.,StructuResearch Group
Composite Structures | Year: 2012

This work focuses on the formulation of an asymptotically correct theory for symmetric composite honeycomb sandwich plate structures. In these panels, transverse stresses tremendously influence design. The conventional 2-D finite elements cannot predict the thickness-wise distributions of transverse shear or normal stresses and 3-D displacements. Unfortunately, the use of the more accurate three-dimensional finite elements is computationally prohibitive. The development of the present theory is based on the Variational Asymptotic Method (VAM). Its unique features are the identification and utilization of additional small parameters associated with the anisotropy and non-homogeneity of composite sandwich plate structures. These parameters are ratios of smallness of the thickness of both facial layers to that of the core and smallness of 3-D stiffness coefficients of the core to that of the face sheets. Finally, anisotropy in the core and face sheets is addressed by the small parameters within the 3-D stiffness matrices. Numerical results are illustrated for several sample problems. The 3-D responses recovered using VAM-based model are obtained in a much more computationally efficient manner than, and are in agreement with, those of available 3-D elasticity solutions and 3-D FE solutions of MSC NASTRAN. © 2012 Elsevier Ltd.

Kelvina Florence S.J.,StructuResearch Group | Renji K.,StructuResearch Group
Journal of Sound and Vibration | Year: 2016

Modal density is an important parameter in Statistical Energy Analysis (SEA) based response estimation. Many space structures use composite cylinders. Modal densities of such structural elements are not reported. In this work an expression for modal density of composite cylindrical shells is derived. Its characteristics and sensitivity to various parameters are discussed. The frequency at which the modal density has a maximum is derived. Modal densities of typical composite cylinders are obtained. It is shown that computing modal density considering an equivalent isotropic cylinder can lead to significant errors. © 2015 Elsevier Ltd. All rights reserved.

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