• Baldev Raj

      Articles written in Sadhana

    • Non-destructive testing and evaluation for structural integrity

      Baldev Raj T Jayakumar B P C Rao

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      Reliable performance of a component or structure depends on pre-service quality of the component and in-service degradation of the component under operating conditions. The role of non-destructive evaluation (NDE) in ensuring pre-service quality and also monitoring in-service degradation to avoid premature failure of the components/structures is ever increasing. There are many NDE techniques based on various physical principles. The end objective of NDE is detection and characterisation of anomalies such as defects, stresses and microstructural degradations in materials. This is accomplished by establishing correlation between a nondestructively measured physical/derived parameter and quantitative information on defects/stresses/microstructures. The NDE information together with design parameters are taken into consideration for evaluation of integrity and life assessment of the components/structures. In this paper, a brief description of the physical concepts of NDE methods and the physical/derived parameters that are used for assessing defects, stresses and microstructures are given. A few case studies highlighting the importance of non-destructive testing and evaluation for structural integrity assessment are also discussed based on the investigations carried out at the authors’ laboratory. Emerging concepts like intelligent processing of materials, expert systems, neural networks, use of multisensors with fusion of data and exploitation of signal analysis and imaging approaches are also addressed in this paper.

    • Meeting the challenges related to material issues in chemical industries

      Baldev Raj U Kamachi Mudali T Jayakumar K V Kasiviswanathan R Natarajan

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      Reliable performance and profitability are two important requirements for any chemical industry. In order to achieve high level of reliability and excellent performance, several issues related to design, materials selection, fabrication, quality assurance, transport, storage, inputs from condition monitoring, failure analysis etc. have to be adequately addressed and implemented. Technology related to nondestructive testing and monitoring of the plant is also essential for precise identification of defect sites and to take appropriate remedial decision regarding repair, replacement or modification of process conditions. The interdisciplinary holistic approach enhances the life of critical engineering components in chemical plants. Further, understanding the failure modes of the components through the analysis of failed components throws light on the choice of appropriate preventive measures to be taken well in advance, to have a control over the overall health of the plant. The failure analysis also leads to better design modification and condition monitoring methodologies, for the next generation components and plants. At the Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam, a unique combination of the expertise in design, materials selection, fabrication, NDT development, condition monitoring, life prediction and failure analysis exists to obtain desired results for achieving high levels of reliability and performance assessment of critical engineering components in chemical industries. Case studies related to design, materials selection and fabrication aspects of critical components in nuclear fuel reprocessing plants, NDT development and condition monitoring of various components of nuclear power plants, and important failure investigations on critical engineering components in chemical and allied industries are discussed in this paper. Future directions are identified and planned approaches are briefly described

    • Development of fuels and structural materials for fast breeder reactors

      Baldev Raj S L Mannan P R Vasudeva Rao M D Mathew

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      Fast breeder reactors (FBRs) are destined to play a crucial role in the Indian nuclear power programme in the foreseeable future. FBR technology involves a multi-disciplinary approach to solve the various challenges in the areas of fuel and materials development. Fuels for FBRs have significantly higher concentration of fissile material than in thermal reactors, with a matching increase in burn-up. The design of the fuel is an important aspect which has to be optimised for efficient, economic and safe production of power. FBR components operate under hostile and demanding environment of high neutron flux, liquid sodium coolant and elevated temperatures. Resistance to void swelling, irradiation creep, and irradiation embrittlement are therefore major considerations in the choice of materials for the core components. Structural and steam generator materials should have good resistance to creep, low cycle fatigue, creep-fatigue interaction and sodium corrosion.

      The development of carbide fuel and structural materials for the Fast Breeder Test Reactor at Kalpakkam was a great technological challenge. At the Indira Gandhi Centre for Atomic Research (IGCAR), advanced research facilities have been established, and extensive studies have been carried out in the areas of fuel and materials development. This has laid the foundation for the design and development of a 500 MWe Prototype Fast Breeder Reactor. Highlights of some of these studies are discussed in this paper in the context of our mission to develop and deploy FBR technology for the energy security of India in the 21st century.

    • Frontiers in materials science and technology - Summary

      Baldev Raj K Bhanu Sankara Rao

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    • Corrosion of bio implants

      U Kamachimudali T M Sridhar Baldev Raj

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      Chemical stability, mechanical behaviour and biocompatibility in body fluids and tissues are the basic requirements for successful application of implant materials in bone fractures and replacements. Corrosion is one of the major processes affecting the life and service of orthopaedic devices made of metals and alloys used as implants in the body. Among the metals and alloys known, stainless steels (SS), Co-Cr alloys and titanium and its alloys are the most widely used for the making of biodevices for extended life in human body. Incidences of failure of stainless steel implant devices reveal the occurrence of significant localised corroding viz., pitting and crevice corrosion. Titanium forms a stable TiO2 film which can release titanium particles under wear into the body environment. To reduce corrosion and achieve better biocompatibility, bulk alloying of stainless steels with titanium and nitrogen, surface alloying by ion implantation of stainless steels and titanium and its alloys, and surface modification of stainless steel with bioceramic coatings are considered potential methods for improving the performance of orthopaedic devices. This review discusses these issues in depth and examines emerging directions.

    • Study of engineering surfaces using laser-scattering techniques

      C Babu Rao Baldev Raj

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      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.

    • A holistic approach to thermomechanical processing of alloys

      S Venugopal Baldev Raj

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      New process design and control methods are needed for significantly improving productivity and reducing costs of thermomechanical processes such as hot metal forging. Current practices for accomplishing basic design tasks such as selecting the number of forming steps and specifying the processing conditions for each thermomechanical operation produce feasible solutions that are often far from optimal. Substantial improvements in effectiveness and efficiency can be realized through holistic approaches that optimize the whole system performance and not just individual subsystems such as workpiece material behavior, material flow in dies, and equipment responses. Recent progress in the application of dynamical modelling and process design techniques using ideal forming concepts and trajectory optimization are discussed. Monitoring methods for the on-line monitoring of the process and an intelligent forging system has been proposed.

    • Overview of pool hydraulic design of Indian prototype fast breeder reactor

      K Velusamy P Chellapandi S C Chetal Baldev Raj

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      Thermal hydraulics plays an important role in the design of liquid metal cooled fast breeder reactor components, where thermal loads are dominant. Detailed thermal hydraulic investigations of reactor components considering multi-physics heat transfer are essential for choosing optimum designs among the various possibilities. Pool hydraulics is multi-dimensional in nature and simple one-dimensional treatment for the same is often inadequate. Computational Fluid Dynamics (CFD) plays a critical role in the design of pool type reactors and becomes an increasingly popular tool, thanks to the advancements in computing technology. In this paper, thermal hydraulic characteristics of a fast breeder reactor, design limits and challenging thermal hydraulic investigations carried out towards successful design of Indian Prototype Fast Breeder Reactor (PFBR) that is under construction, are highlighted. Special attention is paid to phenomena like thermal stratification, thermal stripping, gas entrainment, inter-wrapper flow in decay heat removal and multiphysics cellular convection. The issues in these phenomena and the design solutions to address them satisfactorily are elaborated. Experiments performed for special phenomena, which are not amenable for CFD treatment and experiments carried out for validation of the computer codes have also been described.

    • Dynamics of plasma expansion in the pulsed laser material interaction

      N Kumar S Dash A K Tyagi Baldev Raj

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      A pulse Nd: YAG laser with pulse duration 5–10 ns, beam radius at focal point 0·2–0·4 mm, wavelengths 1064 nm, 532 nm and 238 nm with linearly polarized radiation and Gaussian beam profile, was impacted on a thin foil of titanium metal for generating plasma plume. Numerically, the above parameters were linked with average kinetic energy of the electrons and ions in the laser-induced plasma. In the present model, electrons having higher velocities are assumed to escape from plasma, that forms a negatively charged sheath around the plasma. It is seen from present computations that the forward directed nature of the laser evaporation process results from the anisotropic expansion velocities associated with different species. These velocities are mainly controlled by the initial dimension of the expanding plasma. An attempt was undertaken to estimate the length of the plume at different ambient gas pressures using an adiabatic expansion model. The rate of the plasma expansion for various Ar+ ion energies was derived from numerical calculations. A numerical definition of this plasma includes events like collisional/radiative, excitation/de-excitation and ionization/recombination processes involving multiples of energy levels with several ionization stages. Finally, based on a kinetic model, the plasma expansion rate across the laser beam axis was investigated.

    • Keyhole depth instability in case of CW CO2 laser beam welding of mild steel

      N Kumar S Dash A K Tyagi Baldev Raj

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      The study of keyhole (KH) instability in deep penetration laser beam welding (LBW) is essential to understand welding process and appearance of weld seam defects. The main cause of keyhole collapse is the instability in KH dynamics during the LBW process. This is mainly due to the surface tension forces associated with the KH collapse and the stabilizing action of vapour pressure. A deep penetration high power CW CO2 laser was used to generate KH in mild steel (MS) in two different welding conditions i.e. ambient atmospheric welding (AAW) and under water welding (UWW). KH, formed in case of under water welding, was deeper and narrower than keyhole formed in ambient and atmospheric condition. The number and dimensions of irregular humps increased in case of ambient and under water condition due to larger and rapid keyhole collapse also studied. The thermocapillary convection is considered to explain KH instability, which in turn gives rise to irregular humps.

    • Melt pool vorticity in deep penetration laser material welding

      N Kumar S Dash A K Tyagi Baldev Raj

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      In the present study, the vorticity of melt motion in the keyhole and weld pool has been evaluated in case of high power CO2 laser beam welding. The circulation of vorticity is obtained as a function of Reynolds number for a given keyhole volume which is linked to Mach number variation. The shear stress and thermal fluxes present in the turbulent pool are linked to diffusivity and Prandtl number variation. It was shown that below a critical value of Rayleigh number, the conduction mode of melt transfer signifying beam absorption becomes dominant. Above this value, convective heat transfer indicates melting and evaporation occurring in the weld pool during laser welding. The evaporative recoil pressure expels the liquid while surface tension and hydrostatic pressure help to retain the melt in the keyhole cavity in this high power laser beam welding. The understanding of several hydrodynamic phenomena occuring in the weld pool is valuable not only for understanding basic mechanistic aspects but also for process optimization involved in laser beam welding.

    • Study of dimensionless quantities to analyse front and rear wall of keyhole formed during laser beam welding

      N Kumar S Dash A K Tyagi Baldev Raj

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      Fluid flow mechanisms present in Keyhole (KH) during Laser Beam Welding (LBW) process influence the associated heat and mass transfer. In an attempt to describe these complexities for eventual optimization of LBW parameters, a dimensionless analysis using Mach (Ma), Raleigh (Ra), Reynolds (Re) and Marangoni (Mg) numbers have been carried out. This analysis describes hydrodynamics of melt and vapour phase appearing in the front and rear wall of KH. The non-dimensional hydrodynamic quantities describe the mechanism behind flow pattern present in meltvapour in terms of ratio of convection–conduction heat transfer occurring within KH. The analysis shows that the higher Marangoni number indicates stronger Marangoni convection in the KH causing relatively higher capillary flow in the melt pool. The laminar-turbulent flow of melt-vapour in KH medium is described in terms of ratio of Reynolds and Mach numbers (Re/Ma). The pressure distribution in the KH accounts for the melt-vapour ejection rate. A relationship between depth and radius of KH has been obtained as a function of delivered laser power.

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