IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

A numerical integration technique utilizing a point source Green's function is introduced to analyze the wave behavior in transversely isotropic-type anisotropic media allowing us to make fast and accurate computations of the acoustic field. The centrifugally cast stainless steel (CCSS) used in nuclear power plants is chosen as a sample medium because of its columnar grain character leading to material anisotropy. A representative number of field profiles are computed and plotted to illustrate the quasi-longitudinal, quasi-transverse, and horizontally-polarized shear wave propagation in a transversely-isotropic medium. Phenomena such as beam skewing, beam splitting, beam focusing, unsymmetrical beams, and other anisotropic effects, some of which are already known from earlier experimental observations, emerge as a computational result of the introduced technique. © 1989 Plenum Publishing Corporation.

World University root node

Department of Mechanical Engineering

Journal of Nondestructive Evaluation

A numerical integration Green's function model for ultrasonic field profiles in mildly anisotropic media

Feature mapping presents us with a novel philosophy in ultrasonic non-destructive evaluation that utilizes maximum information from different data acquisition and signal feature domains for possible complete material characterization and defect analysis in a variety of different materials and structures. Feature mapping is a powerful technique that covers a wide area of data acquisition and analysis techniques applying both physically and statistically based principles. This procedure, beyond standard normal beam applications, employs many seldom used but interesting data collection procedures such as critical angles, surface waves, plate waves and backscattering techniques. It forms these into an extremely versatile data acquisition protocol, followed by detailed analysis through a state of the technology signal processing, pattern recognition and expert system and/or artificial intelligence implementation practice. This Paper explains the various existing possibilities for clever physically based data collection, and the types of feature domains and features available for anomaly representation in materials. Typical results are discussed to illustrate the capabilities and utilities of the feature mapping techniques, including a normal beam longitudinal wave high frequency area ratio feature mapping (F-map) system, oblique incidence shear wave amplitude F-maps, and plate leaky wave amplitude F-map results for interfacial weakness in an adhesive bond structure. Also discussed are the results from a normal beam longitudinal wave amplitude and frequency bandwidth F-map for crack detection in a composite material, as well as a backscattered energy F-map for defect edge detection in composite materials. © 1988.

Ultrasonics

Utility of feature mapping in ultrasonic non-destructive evaluation

A numerical integration ultrasonic field analysis computation model is outlined and a variety of experimental and analytical techniques are illustrated for characterizing the anisotropic nature and the corresponding grain structure associated with centrifugally cast stainless steel. The feasibility of using simple techniques such as skip distance, critical angle, and surface wave velocity measurements to obtain preliminary material properties is demonstrated. The question of choosing the proper propagation mode from which the direction of the anisotropic vector can be established is addressed. Ultrasonic field and phase velocity profiles are given and skew angles are graphed and compared to experimental and classical techniques.

Review of Progress in Quantitative Nondestructive Evaluation

Wave scattering and guided wave considerations in anisotropic media

The Oblique Incidence technique proposed here, utilizes shear waves, obliquely incident upon an interface, in a physically based feature analysis process. Guidelines for the data collection process are selected from numerically established reflection factor curves using a theoretical model of the interface between two solid materials with different rigidities of connection. The additional sensitivity of the shear waves can be anticipated from the existence of the tangential components of displacements which are more sensitive to interfacial weaknesses. Also the frequency and angle dependence of the reflectivity from an imperfect interface has led us to the possibility of using the relevant feature combinations as dictated by our model.

American Society of Mechanical Engineers, Materials Division (Publication) MD

Oblique incidence feature mapping techniques for the NDE of adhesive bonds

The problem of surface and bulk wave propagation in a composite material is addressed so that applications in Nondestructive Evaluation can be considered, emphasis in this paper being placed on bulk wave propagation. Global material property determination is considered in an inverse wave velocity computation of stiffness coefficients based on principles from anisotropic elasticity. A one-sided inspection technique based on practical considerations of a field environment is developed. The concept of a feature matrix, based on the stiffness coefficients, is then introduced as a means of material characterization and defect analysis in composite materials. A brief discussion on a test protocol and an interpretation of the elements in the feature matrix from an NDE point of view is also presented. The conclusions of a previous theoretical investigation of wave propagation in anisotropic media are considered from an experimental point of view by way of the bulk wave technique. A result of fundamental value is that the actual propagation of quasilongitudinal waves, generated by a standard broad band pulsed transducer, is indeed well matched with the theoretical approximation obtained earlier.

Elements of an ultrasonic feature matrix NDE technique based on bulk waves and anisotropic elasticity

The use of ultrasonic guided waves has been identified as a promising technology for continuous monitoring of pipe structures to detect small defects of cross-sectional area ratio less than 5%. This paper presents an effective approach to use torsional guided wave mode T(0,1) in thin and small diameter stainless steel tubes operating at elevated temperatures in the range of 150 oC. for detecting small pitting defects using magnetostriction sensors. The phenomenon of scattering of the fundamental torsional mode T(0,1) from complex-shaped discontinuities in thin tubes is closely examined, and its excitation parameters are optimized to an extent using finite element (FE) simulations. From the numerical and experimental results, the optimized design for transmitting/receiving pure torsional modes are investigated. Then, the reflection from three dimensional (3D) notches with varying depth profiles in thin tubes is studied. The results show that the reflection coefficient of torsional guided wave mode T(0,1) is a stronger function of the through-thickness depth and, axial and circumferential extent of the notch. As a result, plots of reflection coefficient as a function of the circumferential extent, axial extent and depth of the defect are shown for particular pipe size. The finite element results are then compared with the experimental data. The sensitivity of the reflected signal from defects up to 2% of the cross-sectional area ratio was examined, and it was found that defects smaller than 2% of the cross-sectional area ratio were detectable. The results from these analyses have been used to propose a practical approach to determine the maximum depth of a pitting defect from the reflection coefficient behaviour, provided that the external circumferential extent or axial extent of the defect is known. This work is of great interest to many process industries including semiconductor manufacturing industries.

SHM of Thin and Small Diameter Tubes Operating at High Temperature for Pitting Corrosion

Graphene Nanoplatelet (GNP)/poly methylmethacrylate (PMMA) based strain sensors were prepared via solution casting process at different initial resistances. The real time strain monitoring capability under various loading conditions (ramp, step and cyclic) and stability of the sensor was explored. The effectiveness of the sensor for crack monitoring in a simple structure was also studied and compared with a standard strain gauge. Experimental results showed a linear change in resistance with the strain in all loading conditions. In cyclic loading at a frequency of 5 Hz, high sensitivity sensors exhibited a considerable amount of time lag for steady response with the strain which was observed to be absent at 0.1 Hz. A significant amount of unrecoverable change in the resistance was observed in the sensors even after unloading, because of which the effective gauge factor of the sensor was reduced. The magnitude of this unrecoverable change in resistance was found to decrease with decrease in the gauge factor and frequency of cyclic loading. However, the GNP/PMMA sensor had shown a greater sensitivity in monitoring a crack in a cantilever beam over a conventional strain gauge.