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.

Probability and Statistical Inference

The Journal of the Acoustical Society of America

Ultrasonic testing of materials: Josef and Herbert Krautkramer Springer-Verlag Publishing Company, Berlin, Heidelberg, New York (1975) 669 pp, $63.00

Review of progress, QNDE

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.

/pdf/x-ray-computed-tomography-for-additive-manufacturing-a-1ouio0owzb.pdf

X-ray computed tomography for additive manufacturing: a review

Online (passive) thermographic inspection of overlap joints of aluminium and zinc coated steel sheets made by cold metal transfer weld brazing process was explored Different experimental trials were conducted for demonstrating the feasibility of thermographic inspection to detect the porosities, improper weld bead and to differentiate the pre weld temperature The whole process was monitored using infrared cameras in different wavelength region Image analysis algorithms were developed to reconstruct the thermal images that contain the signatures of the weld defects and to extract the pre weld temperature and its evolution with distance from the centre of the weld torch Post-weld radiography lends strong support to the observations

/pdf/online-monitoring-of-cold-metal-transfer-cmt-process-using-2h6km2x257.pdf

Online monitoring of cold metal transfer (CMT) process using infrared thermography

A solution to the problem of improving the finite element (FE) modeling of elastic wave‐defect interaction is sought by reconsidering the conventional opinion on meshing strategy. The standard approach using uniform square elements imposes severe limitations in representing complex defect outlines but this is thought to improve when the mesh is made finer. Free meshing algorithms available widely in commercial packages of late can cope with difficult features well but they are thought to cause scattering by the irregular mesh itself. This paper examines whether the benefits offered by free meshing in representing defects better outweigh the inaccuracies due to mesh scattering. If using the standard mesh, the questions whether mesh refinement leads to improved results and whether a practical strategy can be constructed are considered.

Towards improved finite element modelling of the interaction of elastic waves with complex defect geometries

Recent developments in metal additive manufacturing (AM) has created a lot of interest in sectors including automotive, aerospace and biomedical engineering. It is imperative that the components manufactured additively be inspected for flaws, mechanical properties and dimensional accuracy. Several non-destructive testing (NDT) techniques such as X-ray computed tomography and conventional ultrasonic testing have been implemented to evaluate the quality of these components. Recently, research has been focused on techniques that can perform non-contact testing and carry out an online inspection layer by layer while the component is being fabricated. Laser based ultrasonic technique has been found to be a promising method owing to its non-contact nature and ability to operate in harsh environments. In our study, narrow band lamb waves were generated using a pulsed Nd-YAG laser system consisting of a spatial array illumination source. The generated wave modes were detected using a two-wave mixing based laser interferometer. The wavelength-matched method enabled generation of specific lamb wave modes for in-situ inspection of additively manufactured components.

/pdf/laser-generation-of-narrowband-lamb-waves-for-in-situ-4iocr1lln1.pdf

Laser generation of narrowband lamb waves for in-situ inspection of additively manufactured metal components

The use of waveguides for ultrasonic transduction is advantageous in numerous applications such as measurement of flow, temperature and material properties under harsh environments. However, typically waveguide transducers do not use any mode control. This paper describes aspects of mode selection for waveguide based transduction of bulk longitudinal ultrasonic waves in a target metallic specimen. It is proposed that specific waveguide modes with suitable modal structure and matched acoustical impedance can significantly enhance the transduction of bulk ultrasonic waves in the specimen sample. Using circular cylindrical waveguides excited by magnetostriction, experimental results guided by finite element simulations and analysis are presented, demonstrating the feasibility of the approach. An example application in the form of a bulk longitudinal wave ultrasonic transducer is also provided illustrating the improvement in the signal quality using the proposed concept.

Selective modal excitation for optimization of waveguide based bulk ultrasonic transducers

This research presents the nonlinear mixing technique of two co-directionally travelling Rayleigh surface waves generated and detected using laser ultrasonics. The optical generation of Rayleigh waves on the specimen is obtained by shadow mask method. In conventional nonlinear measurements, the inherently small higher harmonics are greatly influenced by the nonlinearities caused by coupling variabilities and surface roughness between the transducer and specimen interface. The proposed technique is completely contactless and it should be possible to eliminate this problem. Moreover, the nonlinear mixing phenomenon yields not only the second harmonics, but also the sum and difference frequency components, which can be used to measure the acoustic nonlinearity of the specimen. In this paper, we will be addressing the experimental configurations for this technique. The proposed technique is validated experimentally on Aluminum 7075 alloy specimen.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=4828&context=qnde

Prabhu Rajagopal

Papers

Online monitoring of cold metal transfer (CMT) process using infrared thermography

Towards improved finite element modelling of the interaction of elastic waves with complex defect geometries

Laser generation of narrowband lamb waves for in-situ inspection of additively manufactured metal components

Selective modal excitation for optimization of waveguide based bulk ultrasonic transducers

Nonlinear mixing of laser generated narrowband Rayleigh surface waves