Department of Mechanical Engineering

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IIT Jodhpur

Polymer matrix based cloth composites are increasingly used in engineering applications. For such composites, significant viscoelastic behavior can be observed for dynamic load conditions. The viscoelastic effect is primarily due to the polymeric matrix used as most of the fibers used in structural applications are elastic. Matrix does not show a major contribution in the axial properties of composites, thus in the traditional modeling its viscoelastic nature is often ignored. However, the effective out of plane properties are influenced by the matrix material and exhibit significant damping characteristics. Therefore, a complete three-dimensional (3-D) model considering the viscoelastic nature of matrix is needed for better understanding of cloth composites. An analytical 3-D micromechanical model based on classical laminate theory (CLT) is verified, in this paper for the prediction of effective elastic and viscoelastic properties of a cloth composite. The method is shown to be accurate. This model is extended to the viscoelastic regime with the use of Laplace transform and correspondence principle. Prony series coefficients for composite cloth are obtained for different volume fractions of fibers in yarn. It is observed from the hysteresis plots that dissipation in out of plane normal and shear modes is significantly higher than the normal directions. © 2011 Elsevier Ltd.

World University root node

Composite Structures

A three-dimensional micromechanical model to predict the viscoelastic behavio of woven composites

Current Science

Feeling: A measurable quantity?

International Journal of Automation and Control

Identification of defects on highly reflective coated ring components using dark field illumination and image segmentation using simple thresholding technique

There exist a huge range of fish species besides other aquatic organisms like squids and salps that locomote in water at large Reynolds numbers, a regime of flow where inertial forces dominate viscous forces. In the present review, we discuss the fluid mechanics governing the locomotion of such organisms. Most fishes propel themselves by periodic undulatory motions of the body and tail, and the typical classification of their swimming modes is based on the fraction of their body that undergoes such undulatory motions. In the angulliform mode, or the eel type, the entire body undergoes undulatory motions in the form of a travelling wave that goes from head to tail, while in the other extreme case, the thunniform mode, only the rear tail (caudal fin) undergoes lateral oscillations. The thunniform mode of swimming is essentially based on the lift force generated by the airfoil like crosssection of the fish tail as it moves laterally through the water, while the anguilliform mode may be understood using the "reactive theory" of Lighthill. In pulsed jet propulsion, adopted by squids and salps, there are two components to the thrust; the first due to the familiar ejection of momentum and the other due to an over-pressure at the exit plane caused by the unsteadiness of the jet. The flow immediately downstream of the body in all three modes consists of vortex rings; the differentiating point being the vastly different orientations of the vortex rings. However, since all the bodies are self-propelling, the thrust force must be equal to the drag force (at steady speed), implying no net force on the body, and hence the wake or flow downstream must be momentumless. For such bodies, where there is no net force, it is difficult to directly define a propulsion efficiency, although it is possible to use some other very different measures like "cost of transportation" to broadly judge performance.

Journal of the Indian Institute of Science

Fluid mechanics of aquatic locomotion at large Reynolds numbers

The focus of this study is on the physical properties of clay ceramic materials compatible for drinking water filtration. A multiparameter lognormal multivariate regression approach is proposed for assessing the combined effects of quantity of compositional constituent of raw materials used in ceramic manufacture on toughness. The approach was validated for two specimen types (T- and S-specimens) derived from a circular base of the frustum shaped, porous clay ceramic ware (PCCW). The PCCW were manufactured from clay and sieved sawdust mixed at distinct volume fractions. The variation of the porosity and density of the PCCW was studied with respect to the amounts of sawdust and clay used in the manufacturing. The research helped to clearly define the roles of clay and sawdust quantities for strength development in both T- and S-specimen. A generalized experimental approach is proposed for estimation of mechanical properties of clay ceramics as a function of the material constituent fractions. A polynomial relationship was developed between the compressive strength and density of the PCCW material. The statistical model expressions developed herein may be used for the prediction of material and mechanical properties of similar materials, including natural and engineered materials. © 2011 American Society of Mechanical Engineers.

Journal of Engineering Materials and Technology, Transactions of the ASME

Physical properties of porous clay ceramic-ware

There are many machining situations where slender tools are used to machine thin walled tubular workpieces. Such instances are more common in machining of aircraft structural parts. In these cases, cutting force induced tool as well as workpiece deflections are quite common which result into surface error on machined components. This paper presents a methodology to compensate such tool and workpiece induced surface errors in machining of thin walled geometries by modifying tool paths. The accuracy with which deflections can be predicted strongly depends on correctness of the cutting force model used. Traditionally employed mechanistic cutting force models overestimate tool and workpiece deflections in this case as the change of process geometry due to deflections is not accounted in modeling. Therefore, a cutting force model accounting for change in process geometry due to static deflections of tool and workpiece is adopted in this work. Such a force model is used in predicting tool and workpiece deflection induced surface errors on machined components and then compensating the same by modifying tool path. The paper also studies effectiveness of error compensation scheme for both synclastic and anti-clastic configurations of tubular geometries. © 2010 Elsevier B.V. All rights reserved.

Journal of Materials Processing Technology

Error compensation in flexible end milling of tubular geometries

Purpose - The purpose of this paper is to present a new numerical approach for modeling the multi-phase flowduring an alloy solidification process. Inmany solidification processes, advection of solid may have a dramatic effect on bulk convection field as well as on the solid front growth and hence on the macro-segregation pattern. In the present work, a numerical model is developed to simulate directional solidification in presence of melt convection as well as solid advection in the form of sedimentation. A 2D cavity filled with hyper-eutectic aqueous ammonium chloride solution (25 wt.% of ammonium chloride) being chilled fromone of the sidewalls has been chosen as themodel problemfor the numerical simulation. Design/methodology/approach - A fixed grid volume averaging technique has been used for solving mass, momentum, energy, and species equation while taking into account the solid phase advection and local re-melting. Two different criteria have been identified for the solid particles in the mushy zone to be mobile. These two criteria are represented by a critical solid fraction, and a critical velocity. Based on these two criteria, the mushy zone has been subdivided into two different regions namely, an immobile coherent zone consisting of packed equiaxed crystals and a mobile non-coherent zone where the solid crystals are able to move. Findings - The numerical results are compared with corresponding experimental observations. Originality/value - The solid advection velocity and source terms dealing with solid velocity have been calculated using an explicit scheme, whereas the main conservation equations are solved using an implicit scheme. © Emerald Group Publishing Limited.

International Journal of Numerical Methods for Heat and Fluid Flow

Modeling of solid phase sedimentation during directional solidification in a side cooled cavity

Non-transferability of fracture data from specimen level to component level is a serious limitation of conventional fracture mechanics, as fracture resistance data obtained is largely geometry dependant. The difficulty is largely overcome by GTN model which models the drop in load carrying capacity of a material with the increase in plastic strain, considering nucleation, growth and coalescence of micro-voids in the material. However, determination of the modelparameters with experiments is extremely difficult and doubtful. Hence, a parameter-study has been done to find out the effects of different parameters on material behaviour to asses the parameter for best practical result with least metallographic study. The parameters were finally verified by predicting ductile fracture in a real life piping component. © 2010 Springer Science+Business Media B.V.