Composites Research Center

Pune, India

Composites Research Center

Pune, India
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Ramadas C.,Composites Research Center | Hood A.,Composites Research Center | Khan I.,Composites Research Center | Balasubramaniam K.,Indian Institute of Technology Madras | Joshi M.,Composites Research Center
Ultrasonics | Year: 2013

Numerical simulations were carried out to quantify the reflection and transmission characteristics of the fundamental Lamb modes propagating in aluminium sub-plates, which are formed due to a semi-infinite horizontal crack. It was observed that, a Lamb mode propagating in a sub-plate when incident at the edge of a crack, undergoes reflection and transmits through the main plate, as well as the other sub-plate. The mode transmitted through the sub-plate has been termed the 'Turning Lamb Mode' (TLM). Furthermore, a mode converted mode also propagates along with the TLM. This mode has been termed the 'Mode Converted Turning Lamb Mode' (MCTLM). Reflection and transmission characteristics of the fundamental Lamb modes in aluminium sub-plates were studied at frequencies 150 kHz, 175 kHz, and 200 kHz. Experiments conducted to validate the observations made in numerical simulations, confirmed that the transmission and reflection characteristics depend on the thickness ratio. From this study it is surmised that when a Lamb mode propagates through a plate containing horizontal crack, the TLM and the MCTLM start propagating from one sub-plate to the other at the rear edge of the crack and amplitude of these modes depends on the location of the crack across the plate thickness. © 2013 Elsevier B.V. All rights reserved.


Anand A.,Composites Research Center | Harshe R.,Composites Research Center | Joshi M.,Composites Research Center
Journal of Composite Materials | Year: 2013

Structural composites based on unidirectional E-glass and epoxy have been fabricated through resin film infusion. Low weight fractions of carbon nanofibers are dispersed in epoxy resin using a solvent-assisted ultrasonication process. Rheological characterization of carbon nanofiber-filled epoxy revealed that viscosity, and in turn processing characteristics of the resin remain almost unaffected as compared to the pristine resin system at elevated temperature of composite processing. Glass transition temperature of epoxy showed a considerable improvement with carbon nanofibers. Local flow of the modified resin through the embedded fabric plies in the resin film infusion process made sure that a uniform distribution of nanoparticles is achieved throughout the composite. Compressive strength of hybrid composites showed over 40% increase while interlaminar shear strength improved by 33% with carbon nanofibers at a loading fraction as low as 0.5 wt%. © 2012 The Author(s).


Chennamsetti R.,Composites Research Center | Khan I.,Composites Research Center
Experimental Techniques | Year: 2016

Air-coupled transducers are successfully employed for selective excitation and reception of Lamb waves in both orthotropic and isotropic plates. While using air-coupled transducers for Lamb wave applications, the transducers are to be set at (1) proper orientation and also (2) they have to satisfy the “co-planarity condition.” Fulfilling these two conditions will result in transmission and reception of high amplitude Lamb wave in the plate. In the present work, one of the misalignments, termed “circumferential misalignment,” is introduced between the air-coupled transmitter and receiver in such a way that the coplanarity condition is violated. In the misaligned configuration, the fundamental antisymmetric Lamb mode (Ao) was transmitted and received. Interestingly, it was found from experiments that, with the increase in severity of the misalignment, amplitude of the Ao mode decreases, and the normalized amplitude of the Ao mode follow the double and the single Gaussian curves in the orthotropic and isotropic plates, respectively. © 2016, The Society for Experimental Mechanics, Inc.


Ramadas C.,Composites Research Center
Journal of Mechanical Science and Technology | Year: 2016

Attenuation of a bulk wave, generated by a point source, propagating in an isotropic medium, is due to the geometry and nature of the material involved. In numerical simulations, if the complete domain of propagation is modeled, then it captures the attenuation of a wave caused due to its geometry. To model the attenuation of the wave caused due to the nature of the material, it is required to know the material’s attenuation coefficient. Since experimental measurement on attenuation of a wave involves both the effects of geometry and material, a method based on curve fitting to estimate the material’s attenuation coefficient from effective attenuation coefficient, is proposed. Using the material’s attenuation coefficient in the framework of Rayleigh damping model, numerical modeling on attenuation of both the bulk waves - longitudinal and shear excited by a point source was carried out. It was shown that the proposed method captures the attenuation of bulk waves caused on account of geometry as well as nature of the material. © 2016, The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.


Anand A.,Composites Research Center | Harshe R.,Composites Research Center | Joshi M.,Composites Research Center
Journal of Applied Polymer Science | Year: 2013

Resin Film Infusion (RFI) has been used to fabricate composites with continuous unidirectional E-glass and epoxy with low weight fractions of carbon nanotubes (CNTs) in matrix. An ultrasound-assisted dissolution-evaporation method with thermoplastics or block copolymers as dispersing agents for nanoparticles enabled uniform dispersion of CNTs in the resin. Rheological characterization of CNT-filled epoxy revealed that viscosity, and hence processing of the resin remains unaffected as compared to pristine resin at elevated temperatures of subsequent composite manufacturing. Local flow of the modified resin through the sandwiched fabric plies in RFI process as against the global flow in traditional liquid composite molding processes, made sure that uniform distribution of nanoparticles is accomplished throughout the composite. Compressive properties of hybrid composites improved considerably with CNTs at loading fractions as low as 0.2 wt %. Copyright © 2012 Wiley Periodicals, Inc.


This paper focuses on transmission characteristics of fundamental symmetric Lamb mode (So) at the junction of a main waveguide and sub-waveguides in composite laminates. Numerical simulations on transmission of So from the main to sub-waveguide revealed that transmission factors of the modes depend on stacking sequence of plies in the waveguides. Experiments were carried out to verify the observations made in numerical simulations. This work gives an insight on the transmission characteristics of So mode while it propagates from a healthy to a delaminated region in a composite laminate. © 2015 Elsevier B.V. All rights reserved.


Ramadas C.,Composites Research Center
Journal of Reinforced Plastics and Composites | Year: 2014

When a Lamb wave propagates in a three dimensional (3D) domain, attenuation i.e. reduction in amplitude of the wave with distance of propagation is due to geometry and material. Experimental measurements of attenuation of a Lamb wave consist of both the effects of geometry and material as well. In the present work, a technique to estimate the attenuation due to material from combined attenuation (geometry and material) was proposed. The estimated material attenuation coefficient was then used in 3D numerical simulations of Lamb wave to capture the combined attenuation. The proposed technique was verified through numerical simulations followed by experimentally measured data on a composite laminate. Furthermore, the entire distance of propagation of a Lamb wave was classified into three regions based on attenuation characteristics. © 2014 The Author(s).


Chennamsetti R.,Composites Research Center
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2013

Numerical simulations followed by experimental validations were carried out to study the interaction of the fundamental Lamb modes when incident at the front edge of a horizontal crack in a metallic plate. During the interaction, the incident fundamental Lamb mode underwent mode conversion and started propagating in the main and sub-waveguides along with the mode-converted Lamb mode. The amplitude of the mode-converted Lamb mode propagating in the main waveguide was negligible compared with that of the incident wave group. It was found that the amplitude of the transmitted Lamb modes from the main waveguide to the sub-waveguides is nearly the same as the incident wave group¿s amplitude; wave groups propagating in the thicker sub-waveguides are found to be carrying higher power than their counterparts in the thinner sub-waveguides. Furthermore, it was observed that variation in power coefficients and amplitude-based factors with respect to frequency of excitation were not very significant. Moreover, it was also shown that amplitude of the reflected wave groups in the main waveguide depends on phase velocities of Lamb modes in the main waveguide and sub-waveguides for a given thickness ratio. © 1986-2012 IEEE.


Singh R.K.,AIR INDIA | Chennamsetti R.,Composites Research Center
International Journal of Precision Engineering and Manufacturing | Year: 2014

Numerical and experimental studies carried out on the propagation of ultrasonic Lamb wave and its interaction with the front edge of a delamination in a cross-ply and unidirectional composite laminates are presented in this paper. When the fundamental antisymmetric Lamb mode (Ao) is incident at the leading (front) edge of a delamination, it undergoes reflection and transmission into the sub-laminates. Numerical simulations carried out on the interaction of the Ao mode with the edge of a semi-infinite delamination revealed that during this interaction, So mode is generated and propagate as AoSo (propagation of the So mode due to the incident Ao mode) mode in the top and bottom sub-laminates along with the incident Ao mode, which propagates as AoAo (propagation of the Ao mode due to the incident Ao mode) mode. Transmission factors and power transmission coefficients of AoAo and AoSo modes on an assortment of excitation frequencies - 150 kHz, 175 kHz, 200 kHz and 225 kHz, and thickness ratios were computed. Experimental validation of results arrived through numerical simulations, was also carried out employing air-coupled ultrasonic transducers. © 2014 Korean Society for Precision Engineering and Springer-Verlag Berlin Heidelberg.


Ramadas C.,Composites Research Center | Hood A.,Composites Research Center | Khan I.,Composites Research Center | Balasubramaniam K.,Indian Institute of Technology Madras
Ultrasonics | Year: 2014

Proper alignment of air-coupled ultrasonic transducers for generation and reception of Lamb waves is vital in order to acquire a high amplitude wave group. Any misalignment with either the transmitter or the receiver or both adversely influences the amplitude of a Lamb mode. This paper reports a systematic attempt to quantify the reduction in the amplitude of the fundamental anti-symmetric Lamb mode (Ao) in a metal plate caused by misalignments in air-coupled probes. Three different types of misalignments - linear, orientation and synchronised orientation were deliberately introduced in the transducers, and experiments were performed on a 6 mm thick aluminium plate. Amplitudes of Ao mode measured at various configurations were normalised with that of Ao mode, captured in a reference configuration. Suitable curves fitted over the experimental data points revealed that Gaussian curves represent appropriately the variations in normalised amplitudes of Ao mode. Moreover, analytical expressions were derived to predict the difference in arrival times of Lamb mode(s) due to orientation and synchronised orientation misalignments. © 2014 Elsevier B.V. All rights reserved.

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