B. Purnachandra Rao

Ensemble Empirical Mode Decomposition based methodology for ultrasonic testing of coarse grain austenitic stainless steels.

A signal processing methodology is proposed in this paper for effective reconstruction of ultrasonic signals in coarse grained high scattering austenitic stainless steel. The proposed methodology is comprised of the Ensemble Empirical Mode Decomposition (EEMD) processing of ultrasonic signals and application of signal minimisation algorithm on selected Intrinsic Mode Functions (IMFs) obtained by EEMD. The methodology is applied to ultrasonic signals obtained from austenitic stainless steel specimens of different grain size, with and without defects. The influence of probe frequency and data length of a signal on EEMD decomposition is also investigated. For a particular sampling rate and probe frequency, the same range of IMFs can be used to reconstruct the ultrasonic signal, irrespective of the grain size in the range of 30-210 μm investigated in this study. This methodology is successfully employed for detection of defects in a 50mm thick coarse grain austenitic stainless steel specimens. Signal to noise ratio improvement of better than 15 dB is observed for the ultrasonic signal obtained from a 25 mm deep flat bottom hole in 200 μm grain size specimen. For ultrasonic signals obtained from defects at different depths, a minimum of 7 dB extra enhancement in SNR is achieved as compared to the sum of selected IMF approach. The application of minimisation algorithm with EEMD processed signal in the proposed methodology proves to be effective for adaptive signal reconstruction with improved signal to noise ratio. This methodology was further employed for successful imaging of defects in a B-scan.

Nondestructive evaluation of austenitic stainless steel welds

The paper presents advanced ultrasonic and eddy current NDE techniques developed in the authors laboratory for nondestructive evaluation of austenitic stainless steel welds. The paper discusses the performance and comparison of 2D discrete wavelet transform (DWT) and de-noising methods applied on eddy current images obtained from stainless steel weld pad with machined longitudinal notches and a systematic approach for eddy current defect characterisation in weld pads by neural network. The simulation and experimental results on the effect of elastic anisotropy on ultrasonic phased array inspection in austenitic stainless steel weld are also discussed. A guided wave based ultrasonic method developed for detection of defects in stainless steel welds and its validation with complimentary techniques such as radiography and in-situ metallography are also presented.

Ultrasonic high-frequency guided waves for the inspection of shell weld in core support structure of fast breeder reactors:

This article reports an ultrasonic high-frequency guided wave based methodology for inspection of shell weld of core support structure of the main vessel in 500-MWe sodium-cooled prototype fast breeder reactor. The high-frequency guided waves are generated in 30-mm-thick plate of core support structure at 2 MHz (frequency–thickness product of ∼60 MHz-mm). These wave modes are fairly nondispersive over considerable distance of propagation through the material. In order to understand the generation and propagation characteristics of these high-frequency guided waves, a series of two-dimensional plane strain finite element models are developed using explicit scheme. The optimum transducer placement for generating efficient high-frequency guided wave is achieved by sweeping the transducer position along the curvature of the main vessel plate with respect to the centerline of the vertical shell support plate. The generated high-frequency guided waves are analyzed and identified with the help of dispersion curves and time–frequency analysis. The simulation results are found to capture the features observed in the experimental measurements rather well, and the time of flight of the reflected waves in the simulation is found to be in excellent agreement with the experimental results. The optimum transducer locations for inspection of a general T-joint configuration with different angles between the web and the base have been studied in detail using finite element simulations. With optimum transducer position, the high-frequency guided waves are also used to inspect the artificially introduced defects in the connecting weld of shell support plate. It has been demonstrated that the high-frequency guided wave could detect defects of 20% wall thickness (6 mm) in the connecting shell weld.

Under sodium imaging of SFR internals - Simulation studies in water

Under sodium viewing at high temperatures is an important requirement in sodium cooled fast reactors (SFR) for navigation during structural inspection. USV is also needed to locate and identify loose parts under sodium, when required. Conventionally, ultrasonic imaging is done using XY raster scanning method. However, due to space constraints within the reactor, it may pose limitations. As an alternative, θ-Z scanning can be used. Ultrasonic image of a typical tool, namely pliers, is obtained using both XY raster scan and θ-Z approaches. Specific software with time of flight correction is developed in LabVIEW for θ-Z based imaging. Comparable images were obtained by both the approaches. CIVA simulation study has also been carried out on a specially designed specimen that simulates various geometries present inside a reactor.

Bulk ultrasonic NDE of metallic components at high temperature using magnetostrictive transducers

Online ultrasonic NDE at high-temperature is of much interest to the power, process and automotive industries in view of possible savings in downtime. This paper describes a novel approach to developing ultrasonic transducers capable of high-temperature in-situ operation using the principle of magnetostriction. Preliminary design from previous research by the authors [1] is extended for operation at 1 MHz, and at elevated temperatures by amorphous metallic strips as the magnetostrictive core. Ultrasonic signals in pulse-echo mode are experimentally obtained from the ultrasonic transducer thus developed, in a simulated high-temperature environment of 350 °C for 10 hours. Advantages and challenges for practical deployment of this approach are discussed.

Development of Automated Scanners for Underwater and Under-Sodium Ultrasonic Imaging

This paper gives an overview of the development of automated scanners for underwater and under-sodium ultrasonic imaging of complex objects in two different scanning modes. The paper deals with the control instrumentation, mechanical movement, degrees of freedom and ultrasonic sensor deployed for the development of the automated scanner.

Prediction of fracture profile using digital image correlation

Digital Image Correlation (DIC) based full field strain mapping methodology is used for mapping strain on an aluminum sample subjected to tensile deformation. The local strains on the surface of the specimen are calculated at different strain intervals. Early localization of strain is observed at a total strain of 0.050ɛ; itself, whereas a visually apparent localization of strain is observed at a total strain of 0.088ɛ;. Orientation of the line of fracture (12.0°) is very close to the orientation of locus of strain maxima (11.6°) computed from the strain mapping at 0.063ɛ itself. These results show the efficacy of the DIC based method to predict the location as well as the profile of the fracture, at an early stage.