Department of Mechanical Engineering

The carbon fiber-reinforced polymeric (CFRP) composite materials are the material of choice for the aircraft structures as the designers require lightweight structures with enhanced mechanical properties. These materials are susceptible to accidental impacts during service and maintenance, and the damage will progress under varying static or dynamic service load conditions leading to the ultimate failure of the component. Recent advancement in non-destructive techniques such as X-ray computed tomography provide excellent details about the presence of damages in 3-Dimension in a component, which is an useful input for failure prediction and remaining life estimation. However, the quality of X-ray CT imaging is dependent on the equipment used, its calibration and image settings which, in turn, may affect the reliability and repeatability of damage quantification, if damage analysis is done in a routine way using binarization algorithms. In this study, the defects as well as the damage present in the low-velocity impacted CFRP laminates subjected to fatigue loading conditions are quantified and analyzed by the analysis of CT scan images obtained from two different CT systems with images of different resolution and contrast. The results of the comparative study show that the damage analysis of polymer composites using X-ray CT depends largely on the image quality and the choice of right threshold level is important for accurate damage estimation.

This paper brings out the phenomenon of flow maldistribution in parallel microchannel systems, which is supposed to have an adverse effect on hot spot formation and temperature distribution in microelectronic devices. An extensive experimental study is carried out where in the parameters affecting the flow maldistribution such as number of channel, area of cross section of the manifold, channel hydraulic diameter, and Reynolds number are varied to study their effect on the pressure drop across the parallel channels designed for liquid cooling of a CPU. It is observed that the flow distribution among the channels improves significantly with a decrease in the channel hydraulic diameter due to higher pressure drop offered by each individual channels simultaneously. This results in a considerable reduction in both the peak temperature and the average temperature of the device with decreasing channel diameters. It is also inferred that the flow maldistribution is relatively invariant with Reynolds number for the microchannel system, which is not the case for the macrochannels. Flow maldistribution is found to increase with increase in number of channels and with a decrease in the manifold area relative to the channel area. The 'I' type flow configuration is found to have the least maldistribution while the 'U' type shows the maximum and Z type falls in between. A simple force analysis of the governing equation in the manifold of the parallel microchannel system reveals a strong dominance of the frictional force over the inertial force and both the forces contribute to the uniform flow distribution at smaller hydraulic diameters, where the 1-D theoretical models failed to achieve a concurrence with the present experimental results. Also the present 3-D numerical simulations give a satisfactory agreement with the experimental results projecting it as an effective tool in the design and analysis of microchannel cooling system. The potential zones of hot spots are identified as low fluid velocity zones or low pressure drop zones among the channels resulting from flow maldistribution. © 2011-2012 IEEE.

Post shutdown decay heat removal in a fast reactor is one of the most important safety functions which must be accomplished with a very high reliability. To achieve high reliability, the fast breeder reactor design has emphasized on passive or near passive decay heat removal systems utilizing the natural convection in the heat removal path. A typical passive decay heat removal system used in recent designs of fast breeder reactors consists of a sodium to sodium heat exchanger and sodium to air heat exchanger which together remove heat directly from the hot pool to the final heat sink, which is air. Since these are safety systems, it is necessary to confirm the design with detailed numerical analysis. The numerical studies include pool hydraulics, natural convection phenomena in closed loops, flow through narrow gaps between SA, multi-scale modeling, etc. Toward understanding the evolution of thermal hydraulic parameters during natural convection decay heat removal, a three-dimensional CFD model for the primary system coupled with an appropriate one-dimensional model for the secondary system is proposed. The model has been validated against the results of natural convection test conducted in PHENIX reactor. Adopting the model for the Indian PFBR, six different decay heat removal cases have been studied which bring out the effect of safety grade decay heat removal system (SGDHRS) capacity, secondary sodium inventory and inter-wrapper flow heat transfer on the subassembly outlet temperatures that are important for safety evaluation of the reactor. From the results, it is concluded that the delay in initiation of SGDHRS, replacement of intermediate sodium in SGDHRS with NaK and a decrease in the AHX air inlet temperature do not change the temperatures of the primary circuit significantly. The secondary sodium inventory plays an important role in reducing the temperatures in the primary coolant. The beneficial effect of inter-wrapper flow heat transfer on primary temperatures is limited to about 20 K in the fissile zone and 50 K in the blanket zone. These results are very important and give direction for future designs of fast breeder reactors. © 2012 Elsevier B.V.

In this work, we propose a new n+1 integration scheme over arbitrary polygonal elements based on centroid approximation and Richardson extrapolation scheme. For the purpose of numerical integration, the polygonal element is divided into quadrilateral subcells by connecting the centroid of the polygon with the mid-point of the edges. The bilinear form is then computed in a two-stage approximation: as a first approximation, the bilinear form is computed at the centroid of the given polygonal element and in the second approximation, it is computed at the center of the quadrilateral cells. Both steps can be computed independently and thus parallelization is possible. When compared to commonly used approach, numerical integration based on sub-triangulation, the proposed scheme requires less computational time and fewer integration points. The accuracy, convergence properties and the efficiency are demonstrated with a few standard benchmark problems in two dimensional linear elasto-statics. From the systematic numerical study, it can be inferred that the proposed numerical scheme converges with an optimal rate in both L2 norm and H1 semi-norm at a fraction of computational time when compared to existing approaches, without compromising the accuracy.

In aircrafts and missiles, actuators are commonly utilized for driving various subsystems including flight control surfaces. Brushless DC motor (BLDC) based electromechanical actuation systems are getting increasingly popular due numerous advantages. Electromechanical Linear actuators (EMLA) are common due to their high torque amplification. The failure modes for these systems transcend electrical, mechanical, and electronic systems are masked by external forces and the dynamic properties of control systems making it difficult to use model based condition monitoring techniques. Generally these systems are stored for longer times before operation, so a comprehensive health monitoring strategy is required for their fault free operation as and when required. The aim of this paper is to identify gear faults signatures in motor current of closed loop electromechanical linear actuators by experimental approach. It also considers the effect of load on the Motor Current Signature Analysis (MCSA) signatures and their comparison with vibration signatures. An amplified error spectrum method devised for such feedback systems was also compared for its fault signature detection capability with vibration and MCSA signatures.

Cell rolling on the vascular endothelium plays an important role in trafficking of leukocytes, stem cells, and cancer cells. We describe a semianalytical model of cell rolling that focuses on the microvillus as the unit of cell-substrate interaction and integrates microvillus mechanics, receptor clustering, force-dependent receptor-ligand kinetics, and cortical tension that enables incorporation of cell body deformation. Using parameters obtained from independent experiments, the model showed excellent agreement with experimental studies of neutrophil rolling on P-selectin and predicted different regimes of cell rolling, including spreading of the cells on the substrate under high shear. The cortical tension affected the cell-surface contact area and influenced the rolling velocity, and modulated the dependence of rolling velocity on microvillus stiffness. Moreover, at the same shear stress, microvilli of cells with higher cortical tension carried a greater load compared to those with lower cortical tension. We also used the model to obtain a scaling dependence of the contact radius and cell rolling velocity under different conditions of shear stress, cortical tension, and ligand density. This model advances theoretical understanding of cell rolling by incorporating cortical tension and microvillus extension into a versatile, semianalytical framework. © 2010 by the Biophysical Society.

The present study is mainly focused on the cutting performance of the micro-scale textured carbide tools while turning AISI 304 austenitic stainless steel under dry cutting environment. The texture on the rake face of the carbide tools was fabricated by laser machining. The cutting performance of the textured tools was further compared with conventional tools in terms of cutting forces, tool wear, machined surface quality and chip curl radius. SEM and EDS analyses have been also performed to better understand the tool surface characteristics. Results show that the grooves help in breaking the tool-chip contact leading to a lesser tool-chip contact area which results in reduced iron (Fe) adhesion to the tool.

A tracked vehicle employs a special transmission to generate a speed difference between the inner and outer tracks for steering. In this paper, the dynamic model of one of the most widely used steering transmissions called double differential steering has been derived and integrated with a multi-body tracked vehicle model. A simplified multi-body model for tracks has been proposed to reduce the computational and numerical difficulties arising from a detailed three-dimensional multi-body model. The accuracy of the proposed model is demonstrated by extensive comparison with a detailed multi-body model developed using the Tracked Vehicle module of the commercial software ADAMS. Simulations are carried out using the integrated tracked vehicle model to demonstrate the effects of changes in three-dimensional vehicle dynamic performance with design changes in powertrain systems.

In this paper we present a novel, practical approach for carrying out distributed high temperature sensing in boilers. We have demonstrated distributed high temperature sensing using fiber Bragg gratings encapsulated inside a rugged mechanical structure. The encapsulation is designed to not only protect the optical fiber from the harsh environment of the boiler, but also to scale the temperature down to a range over which the gratings are relatively stable. A key aspect of our work is the use of a Bayesian inference technique to retrieve the temperature outside the encapsulation within < 1°C accuracy based on the temperature measured by the fiber Bragg grating (FBG).

This paper analyses the damping characteristics of a titanium shell with a magnetostrictive layer bonded to it. The magnetostrictive layer produces an actuating force required to control vibration in the shell, based on a negative velocity feedback control law. The control input is the current to the solenoid surrounding the shell. In the present study, a finite element formulation, physically consistent with the problem has been developed. Vibration reduction in the shell by changing the position of the magnetostrictive layer and its current carrying actuating coil pair along the shell is investigated. © 2003 Elsevier Science Ltd. All rights reserved.