C. Babu Rao

Laser induced structural and microstructural transformations of plasma sprayed Al2O3 coatings

Abstract Air plasma sprayed Al2O3 coatings on metallic substrates suffer from porosities and metastable polymorphs. In this study, laser treatment employed to improve the coating properties resulted in transformation of the as-sprayed coating predominantly consisting of metastable γ-Al2O3 into thermodynamically stable α-Al2O3 phase with enhanced microhardness and reduced surface roughness.

Morphological approach to extract ridge and valley connectivity networks from Digital Elevation Models

The extraction of ridge and valley connectivity networks is essential for studying spatio-temporal organizations. Extraction of such connectivity networks from multiscale DEMs has lately received notable attention. A simple method is proposed to extract these networks, from a sample DEM as well as a simulated fractal DEM, using non-linear morphological transformations in a methodical way. Further, the proposed method can be adapted to extract these complex topological networks from DEMs generated from either remotely sensed or topographic data.

Study of engineering surfaces using laser-scattering techniques

Surface roughness parameters are described. Various surface characterization techniques are reviewed briefly. Interaction of light with the surface is discussed. Laser-scattering methods to characterise the surface are detailed. Practical cases, where laser-scattering methods have provided useful information about surface characteristics, are illustrated.

Simulation of eddy current signals from multiple defects

The application of eddy current testing for structural integrity assessment of heat exchangers is a well established practice. Service induced multiple defects in heat exchanger tubes produce difficult-to-evaluate complicated impedance plane trajectories during periodic eddy current examinations. Finite element simulations carried out to analyse interactions in a two-defect system are discussed. Probable uncertainty in the interpretation of eddy current trajectories is highlighted. Systematic analysis of the results from these studies will simplify procedures for on-line evaluation of eddy current signals.

One-dimensional temperature reconstruction for Raman distributed temperature sensor using path delay multiplexing

The laser pulse width is the limiting factor for high spatial resolution measurement with a Raman distributed temperature sensor (RDTS). A 5 ns laser pulse from a RDTS system has a spatial resolution of 1 m. A methodology is proposed to improve this spatial resolution limit.

On the computation of the Minkowski dimension using morphological operations

The Minkowski dimension as a complexity measure, and its relation to the other dimensions in the case of self‐similar fractal objects, is discussed. An implementation of the Minkowski dimension, using morphological operations on a square grid, is presented. The effect of resolution, orientation and the symmetry of the structuring element used on the estimation of the Minkowski dimension is studied. The corrections required for free end points are presented.

Raman distributed sensor system for temperature monitoring and leak detection in sodium circuits of FBR

Leak detection in coolant loops of nuclear reactors is critical for the safety and performance of the reactors. The feasibility of using Raman distributed temperature sensor (RDTS) has been studied on a 30m test loop. Temperature in sodium circuits of fast Breeder Reactor (FBR) exceeds 550°C, gold coated fiber is chosen as sensor fibers. Leak is simulated through an artificial micro fissure integrated in the test loop with provision for controlled leak rate. The results are discussed in the paper.

Is the spatial organization of larger water bodies heterogeneous

The intuitive argument is that the spatial organization of larger water bodies is more heterogeneous than that of smaller water bodies. To validate this argument, a section containing a large number of water bodies was distributed according to size by following a multiscale opening transformation. A self-similar iterated bisecting process was followed to observe the probability distribution (division rate) pattern of all the size distributed water bodies. These observed probability distributions conformed well to that of the values computed from a binomial multiplicative process. Hence, f- f multifractal spectra were constructed for all the distributed sections containing water bodies of different sizes, and it was found that the degree of heterogeneity in the spatial organization increased with the increasing size category of the water bodies, as the estimated generalized information dimensions from spectra are in an increasing order.

An optical technique for the detection of surface defects in ferromagnetic samples

We discuss the details of a new optical technique developed for the detection of defects in ferromagnetic materials or components, using a ferrofluid emulsion. This new flux leakage probe consists of a monodispersed ferrofluid either confined between two thin transparent sheets or in a cuvette, and a white light source for illumination. By employing ferrofluid droplets of suitable size and surfactant concentration, and mounting the cell on the test specimen surface, one can detect the region where the defect is located in the test specimen by visually observing a colour change in the ferrofluid cell, in the vicinity of the defect. The origin of this colour change in the backscattering direction is Bragg scattering from the droplet chains, which are formed by the leaked magnetic flux in the presence of a defect. The details of the defect detection procedure and typical experimental results obtained in a ferromagnetic specimen with a rectangular slot (i.e. an artificial defect) are presented.

Fiber optic sensors for monitoring sodium circuits and power grid cables

At Kalpakkam, India, a programme on development of Raman Distributed Temperature sensor (RDTS) for Fast Breeder Reactors (FBR) application is undertaken. Leak detection in sodium circuits of FBR is critical for the safety and performance of the reactors. It is demonstrated that RDTS can be usefully employed in monitoring sodium circuits and in tracking the percolating sodium in case of any leak. Aluminum Conductor Steel Reinforced (ACSR) cable is commonly used as overhead power transmission cable in power grid. A second application demonstrates the suitability of using RDTS to monitor this transmission cable for any defect.