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

The interaction of the fundamental shear horizontal (SH0) mode with cracks in isotropic plates in the context of array imaging using ultrasonic guided waves is a subject of continued interest to the authors. Previous work [1–3] in this regard has illuminated different aspects of the scattering of circular crested SH0 waves from through‐cracks. In this paper, the relationship between the scattering from part‐ and through‐thickness cracks is explored. First a framework for such a relationship is proposed, in which the scattering from part‐ and through‐thickness cracks are related by a suitable correction factor. The limits of the model are then tested using results from FE simulations of the problem for different configurations.

Scattering of the fundamental shear horizontal mode by part‐thickness surface‐breaking cracks in an isotropic plate

This paper addresses a gap in the literature on the 3-dimensional scattering of the fundamental symmetric Lamb mode S0 from delimitations in composite plates. We study the scattering of low-frequency S0 Lamb mode from a delamination in a stiffened 4-ply CFRP composite plate with [0/0]S ply orientation. Far field scattering coefficients for the S0 Lamb mode are plotted as a function of circumferential position around the delamination using 3D FE simulations. Results show that the delamination size has less influence on S0 Lamb wave scattering in the low-frequency regime where the S0 mode is non-dispersive. Further analysis was done using two-dimensional FE simulation for different ply-layup orientations with S0 Lamb mode. This study shows that ply-layup orientation and through-thickness delamination location in fiber composite laminate have a significant influence on S0 Lamb mode interaction. We also analyzed the interaction of A0 Lamb mode for a few cases. This work will be useful for practical Lamb wave ...

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=4985&context=qnde

Interaction of guided waves with delaminations in composite plate structures

Experimental results on deep subwavelength resolution of defects are presented for the first time in the context of guided ultrasonic wave inspection of defects, using novel “structured channel” metamaterials. An Aluminum bar with side-drilled holes is used as a test sample, interrogated by the fundamental bar-guided symmetric mode. Simulations were conducted to optimize dimensional parameters of the metamaterial structure. Experiments using metamaterials fabricated accordingly demonstrate a resolution down to 1/72 of the operating wavelength, potentially bringing the resolution of guided wave inspection to the same range as that of bulk ultrasonics. This work has much promise for remote inspection in industry and biomedicine.

/pdf/structured-channel-metamaterials-for-deep-sub-wavelength-du8yma11sm.pdf

Structured channel metamaterials for deep sub-wavelength resolution in guided ultrasonics

One-dimensional phononic crystals made of silicon (Si) and germanium (Ge), both of which are materials commonly used in semiconductor devices, are shown to be effective in inducing bandgaps in the dispersion of heat flow at the nanoscale. Numerical approaches are used to understand the dispersion and propagation of thermal waves in Si–Ge phononic crystals. The results show for the first time how nanostructuring could yield band gaps in the dispersion of thermal phonons in the GHz range. We arrive at conditions that can yield bandgaps as high as 40 GHz; this is a bandgap that exceeds the value reported thus far. Variations in the unit cell dimensions are studied to understand the corresponding evolution in the bandgap frequencies. The control of heat using such proposed media holds promise for better heat management solutions for modern electronic devices, nanoscale sensing as well as for novel applications including the development of thermal diodes and thermal cloaks.

Semiconductor-based thermal wave crystals

Conventional rotary thrusters used in underwater Remotely Operated Vehicles (ROV) suffer from disadvantages such as high noise, entangling with floating objects and limited efficiency. Our group has studied bio-inspired propulsion with a single caudal fin which overcomes some of these disadvantages. However, it still faces some problems such as low thrust density (thrust generated per unit volume of the thruster), pitch/yaw and centre of mass (COM) oscillations in the body increasing the energy cost of transport. The solution being proposed is a novel dual flapping foil arrangement actuated using a single motor which tackles the limitations of single flapping foil. Comparison of efficiency, maximum thrust and thrust density has been performed between single and dual flapping foil propulsion. Also, this solution is benchmarked against commercially available rotary thrusters. The results showed that thrust density of bioinspired propulsion was not at par with rotary thrusters. However, the efficiency obtained was comparable.

Prabhu Rajagopal

Papers

Scattering of the fundamental shear horizontal mode by part‐thickness surface‐breaking cracks in an isotropic plate

Interaction of guided waves with delaminations in composite plate structures

Structured channel metamaterials for deep sub-wavelength resolution in guided ultrasonics

Semiconductor-based thermal wave crystals

Comparison of bio-inspired flapping foil propulsion systems with rotary propulsion