C. Lakshmana Rao

Bio: C. Lakshmana Rao is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Time-of-flight diffraction ultrasonics & Buckling. The author has an hindex of 12, co-authored 57 publications receiving 702 citations. Previous affiliations of C. Lakshmana Rao include Indian Institutes of Technology.

Extraction of bamboo fibers and their use as reinforcement in polymeric composites

Abstract: Few investigations have been carried out with bamboo fibers despite its high strength, biodegradability, and low cost. The overall objective of this work was to investigate fiber extraction from bamboo and the use of these bamboo fibers as reinforcement in polymeric composites. A combination of chemical and mechanical methods was used for the extraction of bamboo fibers. Conventional methods of compression molding technique (CMT) and roller mill technique (RMT) were explored for the mechanical separation. Fiber population from both the techniques were characterized. Mechanical properties of the fibers also were evaluated. Bamboo fibers obtained from CMT and RMT were used to make unidirectional composites of polyester. High values of tensile strength were observed in all the composites. The predominant mode of failure for the composite was shown to be the cracking of the fiber–matrix interface. Quantitative results from this study will be useful for further and more accurate design of bamboo reinforced composite materials. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 83–92, 2000

Large deflection of constant curvature cantilever beam under follower load

Abstract: This paper describes a method to analyze for the large deflections of curved prismatic cantilever beams with uniform curvature subjected to a follower load at the tip. The large deflection, the deflection dependent follower load and the initial curved geometry are the important features of the beam considered in this work. Shear force formulation proposed by Lee [Large deflections of cantilever beams of non-linear elastic material under a combined loading. Int J Non-Linear Mech 2002;37(3)] is used for deriving the governing equations. Using this approach, the resulting two point boundary value problem (TPBVP) can be reduced to an initial value problem (IVP). Fourth order Runge–Kutta method along with one parameter reverse shooting method is applied to the numerical solution to the problem. A novel approach presented in this paper of integrating from the free end to the fixed end of the cantilever beam simply replaces the two parameter shooting with a single parameter shooting yielding several advantages. This solution technique is demonstrated for various types of follower tip loads on curved and straight cantilever beams and is validated with existing solutions in the literature.

Mechanics of air voids reduction of asphalt concrete using mixture theory

Abstract: Asphalt concrete used in flexible highway pavements has 5–8% air voids immediately after laying of the roadway. Constitutive laws for asphalt concrete developed till now have modelled the mix as a linear elastic or viscoelastic material and have not taken into account the effect of voids concentration on the mechanical behaviour of the material. In the present study the theory of mixtures is used to model asphalt concrete. Asphalt concrete is considered to be a mixture of aggregate matrix, asphalt and air in a purely mechanical system in which the thermal effects and chemical reactions are ignored. Constitutive relation for each component of the mixture is assumed to be dependent only on the kinematical quantities associated with each component. The resulting hyperbolic conservation equations are solved by an upwind finite volume scheme coupled with an operator splitting technique for a quasi-static type of loading. The numerical scheme is used to simulate the variation of air voids content across the thickness of a typical road pavement.

Shear-wave time of flight diffraction (S-TOFD) technique

Abstract: Ultrasonic time of flight diffraction (TOFD) for sizing defects is based on the time of flight of the diffracted echo that is generated when a longitudinal wave is incident on a crack tip. This technique has the limitation during near-surface inspection due to signal superposition. Here, this limitation is overcome by using the shear wave-diffracted signal (instead of longitudinal wave) and hence called S-TOFD. Experiments were conducted on samples with defect tip closer to the surface of a flat plate sample to illustrate the utility of the S-TOFD technique. An increase in the flaw sizing accuracy, by using the shear wave-diffracted echoes from the tip and through the application of a signal processing technique (ESIT), was demonstrated.

Permeability and bleeding of asphalt concrete using mixture theory

Abstract: Distress due to water induced damage and bleeding accelerates the failure of an asphalt concrete pavement due to damage mechanisms such as fatigue cracking, rutting, stripping etc. One of the important variables used while modeling water induced damage for asphalt concrete pavement is permeability. This study uses the framework developed to model the movement of air voids in asphalt concrete in a previous study by the authors [cf. J. Murali Krishnan, C. Lakshmana Rao, International Journal of Engineering Science, 38 (2000) 1331]. The assumption of constant permeability in the theory of consolidation by Terzaghi is relaxed and a linear relation is proposed between permeability and air voids. Voids filled with asphalt (VFA) are proposed as a parameter to model bleeding of asphalt concrete, and its variation for different loading and mixture condition is studied.

Auxetic metamaterials and structures: a review

Abstract: Materials and structures with negative Poisson's ratio exhibit a counter-intuitive behaviour. Under uniaxial compression (tension), these materials and structures contract (expand) transversely. The materials and structures that possess this feature are also termed as 'auxetics'. Many desirable properties resulting from this uncommon behaviour are reported. These superior properties offer auxetics broad potential applications in the fields of smart filters, sensors, medical devices and protective equipment. However, there are still challenging problems which impede a wider application of auxetic materials. This review paper mainly focuses on the relationships among structures, materials, properties and applications of auxetic metamaterials and structures. The previous works of auxetics are extensively reviewed, including different auxetic cellular models, naturally observed auxetic behaviour, different desirable properties of auxetics, and potential applications. In particular, metallic auxetic materials and a methodology for generating 3D metallic auxetic materials are reviewed in details. Although most of the literature mentions that auxetic materials possess superior properties, very few types of auxetic materials have been fabricated and implemented for practical applications. Here, the challenges and future work on the topic of auxetics are also presented to inspire prospective research work. This review article covers the most recent progress of auxetic metamaterials and auxetic structures. More importantly, several drawbacks of auxetics are also presented to caution researchers in the future study.

Bamboo fibre reinforced biocomposites: A review

Abstract: The reduction in harmful destruction of ecosystem and to produce low cost polymeric reinforced composites, the researchers are emerging with policies of manufacturing the composites using natural fibres which are entirely biodegradable. These policies had generated safe strategies to protect our environment. The utilization of bamboo fibres as reinforcement in composite materials has increased tremendously and has undergone high-tech revolution in recent years as a response to the increasing demand for developing biodegradable, sustainable, and recyclable materials. The amalgamation of matrix and natural fibres yield composite possessing best properties of each component. Various matrices used currently are soft and flexible in comparison to natural fibres their combination leads to composite formation with high strength-to-weight ratios. The rapid advancement of the technology for making industry products contributes consumer the ease of making a suitable choice and own desirable tastes. Researchers have expanded their expertise in the product design by applying the usage of raw materials like bamboo fibre which is stronger as well as can be utilized in generating high end quality sustainable industrial products. Thereby, this article gives critical review of the most recent developments of bamboo fibre based reinforced composites and the summary of main results presented in literature, focusing on the processing methodology and ultimate properties of bamboo fibres with polymeric matrices and applications in well designed economical products.

Extraction and tensile properties of natural fibers: Vakka, date and bamboo

Abstract: This paper aims at introducing new natural fibers used as fillers in a polymeric matrix enabling production of economical and lightweight composites for load carrying structures. An investigation of the extraction procedures of vakka (Roystonea regia), date and bamboo fibers has been undertaken. The cross-sectional shape, the density and tensile properties of these fibers, along with established fibers like sisal, banana, coconut and palm, are determined experimentally under similar conditions and compared. The fibers introduced in the present study could be used as an effective reinforcement for making composites, which have an added advantage of being lightweight.

Natural Fibers as Sustainable and Renewable Resource for Development of Eco-friendly Composites: A Comprehensive Review

Abstract: The increase in awareness of the damage caused by synthetic materials on the environment has led to the development of eco-friendly materials. The researchers have shown a lot of interest in developing such materials which can replace the synthetic materials. As a result, there is an increase in demand for commercial use of the natural fiber-based composites in recent years for various industrial sectors. Natural fibers are sustainable materials which are easily available in nature and have advantages like low-cost, lightweight, renewability, biodegradability and high specific properties. The sustainability of the natural fiber-based composite materials has led to upsurge its applications in various manufacturing sectors. In this paper, we have reviewed the different sources of natural fibers, their properties, modification of natural fibers, the effect of treatments on natural fibers, etc. We also summarize the major applications of natural fibers and their effective use as reinforcement for polymer composite materials.

Electrospun nanofiber reinforced composites: a review

Abstract: This paper provides a comprehensive overview on the properties of electrospun nanofibers and their application as reinforcements in composites. The paper first introduces the remarkable properties of electrospun nanofibers including high aspect ratio and molecular orientation, large specific surface area, small pore size, as well as excellent mechanical performance. Next the fabrication methods for the electrospun nanofiber reinforced composites are described. Then different kinds of electrospun nanofiber reinforced composites are discussed in terms of the classifications of electrospun nanofibers. After that, the influences of the mechanical performance of fibers, fiber diameter, fiber amount, fiber/matrix interfacial interaction and the distribution of fibers in the matrix on the reinforcement of composites are discussed. At the end, the possible future challenges and conclusions for electrospun nanofiber reinforced composites are highlighted.