Prabhu Rajagopal

Bio: Prabhu Rajagopal is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Ultrasonic sensor & Guided wave testing. The author has an hindex of 18, co-authored 129 publications receiving 1035 citations. Previous affiliations of Prabhu Rajagopal include Imperial College London & Indian Institutes of Technology.

Longitudinal guided waves confined in radius filler regions of composite joints.

Abstract: This paper studies the feasibility of using ultrasonic guided waves for fast inspection of conformal deltoid radius filler or “Noodle” regions of joints in stringer composite structures. Semi-analytical finite element simulations, supported by experiments and three-dimensional finite element models, are used to demonstrate the existence of a longitudinal guided ultrasonic mode confined or trapped in the Noodle regions. Studies reveal that this mode has attractive properties for rapid screening of Noodle joints, including strong energy concentration, low dispersion, and attenuation. Discussing the physics of mode confinement in light of material differences and geometry, the phenomenon is shown to be related to feature-guiding effects noted in literature recently.

A transformation elasticity based device for wavefront manipulation

Abstract: The authors propose a metamaterial plate made of gradient refractive index phononic crystals for manipulation of the wavefront of propagating elastic waves in solid media. A square unit cell with through holes is considered as the basis for the proposed metematerial. Guidance on the design of the hole pattern and the choice of materials is obtained with the aid of transformation elasticity principles. Manipulation of a plane wavefront into a cylindrical wavefront is first observed through Finite Element simulations at low frequency (100 kHz), and then practically demonstrated through experiments. Wave propagation with and without the holey region is compared and possible applications at higher frequencies are discussed.

In-situ process- and online structural health-monitoring of composites using embedded acoustic waveguide sensors

Abstract: This article reports the development of a novel embedded acoustic waveguide sensor concept for monitoring the curing process and online health of composite structures. A sleeved waveguide embedded in the composite is proposed to confine guided waves in one dimension, with leakage to the surrounding media only through specially created openings, thus enhancing the capability to inspect large structures. The method is first developed using a rectangular copper strip embedded in an epoxy plate structure having an artificial delamination-type defect. Finite element simulations are used to gain insights on parameters and limitations. The approach is also demonstrated on a more practical bi-layer composite plate with an artificial delamination and an embedded wire waveguide sensor.

Wind turbine blades inspection techniques

Abstract: Wind turbines are complex composite structures, which condition should be constantly tested. In this paper the techniques which are already used or are implementable for non-destructive examination of wind turbine blades will be presented shortly. New electromagnetic techniques like active IR testing or terahertz imaging will be more widely presented and some exemplary results of inspections will be shown. Streszczenie. Turbiny wiatrowe są złożonymi strukturami kompozytowymi, których stan powinien być stale badany. W niniejszym opracowaniu krótko przedstawiono metody nieniszczącego badania łopat turbin wiatrowych, które są obecnie stosowane lub są możliwe do wdrożenia. Nowe techniki wykorzystujące zjawiska elektromagnetyczne, jak aktywna inspekcja w podczerwieni, czy obrazowanie terahercowe, zostaną szerzej omówione. Zaprezentowane zostaną również przykładowe wyniki badań. Metody nieniszczącego badania łopat turbin wiatrowych

Probability and Statistical Inference

Abstract: The Foundations of Statistics By Prof. Leonard J. Savage. (Wiley Publications in Statistics.) Pp. xv + 294. (New York; John Wiley and Sons, Inc.; London: Chapman and Hall, Ltd., 1954.) 48s. net.

X-ray computed tomography for additive manufacturing: a review

Abstract: In this review, the use of x-ray computed tomography (XCT) is examined, identifying the requirement for volumetric dimensional measurements in industrial verification of additively manufactured (AM) parts. The XCT technology and AM processes are summarised, and their historical use is documented. The use of XCT and AM as tools for medical reverse engineering is discussed, and the transition of XCT from a tool used solely for imaging to a vital metrological instrument is documented. The current states of the combined technologies are then examined in detail, separated into porosity measurements and general dimensional measurements. In the conclusions of this review, the limitation of resolution on improvement of porosity measurements and the lack of research regarding the measurement of surface texture are identified as the primary barriers to ongoing adoption of XCT in AM. The limitations of both AM and XCT regarding slow speeds and high costs, when compared to other manufacturing and measurement techniques, are also noted as general barriers to continued adoption of XCT and AM.