Showing papers by "Anish Kumar published in 2014"
TL;DR: In this article, the feasibility of using Finite Element (FE) simulations to augment sparse measurements made using experiments, and predict PoD curves for ultrasonic inspection of stainless steel plates and welds was reported.
13 citations
TL;DR: In this article, a finite element modeling of spiral coil electromagnetic acoustic transducers (EMATs) to generate sound wave modes is discussed, which is used to predict the ultrasonic A-scan signals of bulk (longitudinal and shear) waves in isotropic homogeneous material.
Abstract: This paper discusses finite element modeling of spiral coil electromagnetic acoustic transducer (EMAT) to generate bulk waves. First, a 2D electromagnetic model is developed for calculating the Lorentz force density, which is the driving force for sound wave generation within the material. Second, the calculated force at each point in the material is used as the driving force for generating sound wave modes. This model is used to predict the ultrasonic A-scan signals of bulk (longitudinal and shear) waves in isotropic homogeneous material. Spiral coil EMATs of two different coil spacings are developed for experimental studies. The model predicted results are validated by experimental results and for this, the ratio of amplitude of shear wave to longitudinal wave is used.
10 citations
TL;DR: In this article, the real and imaginary part of the contact stiffness k* is determined from the contact-resonance spectra obtained, and from these two quantities the local damping factor Qloc−1 is obtained, which is proportional to the imaginary part γ of contact stiffness.
Abstract: Atomic force acoustic microscopy (AFAM), an advanced scanning probe microscopy technique, has been used to measure local elastic properties with a spatial resolution given by the tip-sample contact radius. AFAM is based on inducing out-of-plane vibrations in the specimen. The vibrations are sensed by the AFM cantilever from by the photodiode signal when its tip is in contact with the material under test. To measure local damping, the inverse quality factor Q−1 of the resonance curve is usually evaluated. Here, from the contact-resonance spectra obtained, we determine the real and imaginary part of the contact stiffness k* and from these two quantities the local damping factor Qloc−1 is obtained which is proportional to the imaginary part γ of the contact stiffness. The evaluation of the data is based on the cantilever's mass distribution with damped flexural modes and not on an effective point-mass approximation for the cantilever’s motion. The given equation is simple to use and has been employed to stud...
9 citations
TL;DR: In this article, the authors describe an approach to eliminate the effect of change in tip condition on mapping of elastic properties by atomic force acoustic microscopy, which involves simultaneous acquisition of two contact resonances and using the contact stiffness of the matrix in every scan line as reference for finding the indentation modulus of fine precipitates.
Abstract: We describe a novel approach to eliminate the effect of change in tip condition on mapping of elastic properties by atomic force acoustic microscopy. The method involves simultaneous acquisition of two contact resonances and using the contact stiffness of the matrix in every scan line as reference for finding the indentation modulus of fine precipitates. The methodology is demonstrated by mapping the indentation modulus of a 200 nm wide delta precipitate in a nickel-base superalloy.
8 citations
TL;DR: In this article, an absolute methodology has been developed for quantification of misalignment of an ultrasonic transducer using a corner-cube retroreflector using amplitude-based and time-of-flight (TOF) based C-scans of the reflector.
6 citations
Journal Article•
2 citations
1 citations
01 Sep 2014
TL;DR: In this paper, various studies carried out in the authors' laboratory for multi-scale microstructural characterization in different metallic structural materials such as nickel base alloys, zirconium alloys and titanium alloys through elastic properties are presented.
Abstract: The paper presents various studies carried out in the authors' laboratory for multi-scale microstructural characterization in different metallic structural materials such as nickel base alloys, zirconium alloys and titanium alloys through elastic properties. The elastic properties are evaluated at macroscale using ultrasonic velocity measurements and at micro/nano scale using atomic force acoustic microscopy. A thickness independent ultrasonic measurement based nondestructive methodology implemented for in-situ assessment of degradation of alloy 625 ammonia cracker tubes in heavy water plants is also discussed.