Research Status

1. Snap-through analysis of multistable laminate using the variational asymptotic method [reference]

• Researcher: Mr. A. Phanendra Kumar

• Collaborators: Mr. Shaikbepari Mohmmed Khajamoinuddin, Prof. Ramesh Gupta Burela, Prof. Vinyas Mahesh

• Supervisor: Prof. Dineshkumar Harursampath

Multistable laminates have attracted the attention of researchers for developing morphing structures, as they can stay in different stable configurations without any need for external forces to maintain any of those configurations. In this study, a novel application of a reconfigurable antenna made with rectangular composite laminates [90/0] in the shape of a star is analyzed using the Variational Asymptotic Method (VAM), which is free of ad-hoc assumptions and highly accurate, unlike semi-analytical theories present in the literature. The star shaped laminate is modeled as a plate using geometrically exact kinematics, and thermal analysis is done by applying uniform temperature to obtain its cool-down shape, which shows multistability. Snap-through forces are applied on the structure to change to the other stable configurations. Three parametric studies are performed to identify the variation of snap-through force. These studies are carried out by varying the aspect ratio, curing temperature, and thickness of the individual rectangular laminates to identify the lower and upper limits beyond which the laminate loses its multistability. All studies performed using VAM are validated against 3D FEA in ABAQUS are found to be in good agreement with each other although, VAM handled the 3D problem at the 2D level achieved by systematic dimensional reduction. The computational efficiency is found to increase by almost 70% compared to 3D FEA.

2. Influence of fibre cross-section profile on the multi-physical properties of uni-directional composites [reference]

• Researchers: Mr. Rajesh Nakka & Mr. A. Phanendra Kumar

• Collaborators: Prof. SA Ponnuswamy

• Supervisor: Prof. Dineshkumar Harursampath

The present work comprehensively examines the influence of fibre-matrix interface perimeter on the multi-physical properties of uni-directional composite materials. Three-dimensional microstructures (containing fibres of triangular, elliptical, rectangular, C-shape and two-lobe cross-section shape) are analysed to evaluate effective thermal conduction, thermo-elastic and piezo-electric properties. Each of these properties is normalised with the respective property of RVE with circular fibre cross-section; These normalised properties are, objectively, compared with the normalised fibre cross-section perimeter (shape factor). For all the considered properties and fibre cross-sectional shapes, a novel observation is that the property experiences a drop (or rise) in the initial range of the shape factor but rises (or drops) monotonically afterwards. This is in contrast with the existing literature observations, where properties are understood to have only a monotonic increase/decrease with the shape factor. Further, it is observed that the magnitude of the initial drop (or rise) is sensitive to the fibre volume fraction and the fibre-matrix property contrast. In accordance with the literature, a strong correlation is observed among the variation of in-plane shear moduli, transverse thermal conduction and transverse dielectric constants. 

3. Computational evaluation of absorption characteristics of ceramic-based auxetic materials in X-band frequency range [reference]

• Researchers: Mr. A. Phanendra Kumar

• Collaborators: Mr. Rajesh Nakka & Prof. SA Ponnuswamy 

• Supervisor: Prof. Dineshkumar Harursampath

This research study investigates the absorption capabilities of ceramic-based auxetic metamaterials within the X-band frequency range, emphasising their potential application in stealth technology. Four distinct auxetic topologies have been chosen for this purpose: star, re-entrant, anti-tetrachiral, and missing-rib/cross-chiral while maintaining an equal cross-sectional area for comparison analysis. A computationally efficient homogenisation scheme based on the variational asymptotic method is used to evaluate the effective properties of these auxetics. The absorption spectra are then obtained by evaluating scattering matrices using these effective properties. The influence of auxetics out-of-plane thickness, incidence and polarisation angles on the proposed ceramic absorber’s absorption spectra is evaluated. One of the interesting observations is the identical absorption capabilities of star and missing rib/cross-chiral geometries despite their distinct architectures. The star and missing-rib/cross-chiral-based absorbers achieved a maximum absorption of 99.99% or a minimum reflection loss (RL) of −40 dB with a thickness of 3.50 mm. The RL is less than −10 dB (the standard for an electromagnetic (EM) absorber) for all incidence angles less than 70◦. The findings of this study hold significant potential for the advancement of ceramic-based auxetic metamaterials in EM absorption applications within the aerospace industry. 

3. Computational evaluation of absorption characteristics of ceramic-based auxetic materials in X-band frequency range [reference]

• Researchers: Mr. A. Phanendra Kumar

• Collaborators: Mr. Rajesh Nakka & Prof. SA Ponnuswamy 

• Supervisor: Prof. Dineshkumar Harursampath

This research study investigates the absorption capabilities of ceramic-based auxetic metamaterials within the X-band frequency range, emphasising their potential application in stealth technology. Four distinct auxetic topologies have been chosen for this purpose: star, re-entrant, anti-tetrachiral, and missing-rib/cross-chiral while maintaining an equal cross-sectional area for comparison analysis. A computationally efficient homogenisation scheme based on the variational asymptotic method is used to evaluate the effective properties of these auxetics. The absorption spectra are then obtained by evaluating scattering matrices using these effective properties. The influence of auxetics out-of-plane thickness, incidence and polarisation angles on the proposed ceramic absorber’s absorption spectra is evaluated. One of the interesting observations is the identical absorption capabilities of star and missing rib/cross-chiral geometries despite their distinct architectures. The star and missing-rib/cross-chiral-based absorbers achieved a maximum absorption of 99.99% or a minimum reflection loss (RL) of −40 dB with a thickness of 3.50 mm. The RL is less than −10 dB (the standard for an electromagnetic (EM) absorber) for all incidence angles less than 70◦. The findings of this study hold significant potential for the advancement of ceramic-based auxetic metamaterials in EM absorption applications within the aerospace industry. 

4. Non-linear buckling analysis of delaminated hat-stringer panels using  variational asymptotic method [reference]

• Researchers: Mr. A. Phanendra Kumar

• Collaborators: Prof. Javier Paz Mendez, Prof. Ramesh Gupta Bureal, Prof. Sathiskumar Ponnusami, Prof. Chiara Bisagni 

• Supervisor: Prof. Dineshkumar Harursampath

This research proposes a computationally efficient methodology using a Constrained Variational Asymptotic Method (C-VAM) for non-linear buckling analysis on a hat-stringer panel with delamination defects. Starting with the geometrically non-linear kinematics, the VAM procedure reduces the three-dimensional (3-D) strain energy functional to an analogous 2-D plate model and evaluates the closed-form warping solutions. Utilising the resulting warping solutions and recovery relations for the skin and the stringer, displacement continuity at the three-dimensional level is enforced between the stringer and the skin based on the pristine and delaminated interface regions. Consequently, the constrained matrices obtained from C-VAM are incorporated into an in-house developed non-linear finite element framework. Using the developed formulation, a stiffened panel with delamination of 40 mm between the stringer and the skin is analysed under compression. The results have been validated locally and globally, employing experimental data and 3-D finite element analysis (FEA). Experiments are carried out on the co-cured panel by applying quasi-static loading with displacement-controlled conditions, and 3-D FEA is carried out in Abaqus. Load-response plots have been obtained to validate the results at the global level, and they are in excellent agreement with experiments and 3-D FEA. Subsequently, out-of-plane displacement contour plots are obtained; the number of half waves and wave intensity in 3-D FEA and C-VAM are comparable, although there are minor differences compared to the experimental findings. The proposed framework is shown to be computationally efficient by over 55% as compared to 3-D FEA for performing non-linear buckling analysis on the stiffened composite structure considered in the current work. 

5. A novel engineered sandwich composite with ceramic-coated graphite fibre-reinforced face sheets and an auxetic core for enhanced broadband electromagnetic absorption: design using multiscale computational analysis [reference]

• Researchers: Mr. A. Phanendra Kumar

• Collaborators: Prof. Sathiskumar Ponnusami

• Supervisor: Prof. Dineshkumar Harursampath

A novel sandwich composite is designed for enhanced broadband absorption using a multiscale computational analysis. The sandwich panel is configured with BaTiO3 coated graphite fibre-reinforced polymer (C-GFRP) composite, while BaTiO3 material is used as the auxetic core material. A computationally efficient in-house tool based on the variational asymptotic method is used to homogenise the electromagnetic properties and evaluate the reflection loss characteristics of the proposed sandwich structure using the scattering matrices. A detailed parametric study of 300 analyses is conducted to identify the optimal sandwich panel configurations for achieving broadband reflection loss under the normal incidence of transverse electric (TE) and transverse magnetic (TM) polarised waves. Two different configurations have been obtained, satisfying the requirements of broadband reflection loss in the X-band frequency range. Configuration (a) Vf = 15% without any ceramic coating, and configuration (b) Vf = 20% with a ceramic coating volume fraction (Cf) of 70%. Configuration (a) and (b) maintained the desired reflection loss of greater than −10 dB up to an incidence angle of 40° and 60°, respectively. With the demonstrated capability of covering the entire broadband frequency range, the proposed configurations can serve as baselines to explore novel ceramic-based engineered composite architectures for broadband absorption applications.