http://ieeexplore.ieee.org/iel5/5/31047/01444179.pdf

Fundamentals of acoustics

The paper provides a state of the art review of guided wave based structural health monitoring (SHM). First, the fundamental concepts of guided wave propagation and its implementation for SHM is explained. Following sections present the different modeling schemes adopted, developments in the area of transducers for generation, and sensing of wave, signal processing and imaging technique, statistical and machine learning schemes for feature extraction. Next, a section is presented on the recent advancements in nonlinear guided wave for SHM. This is followed by section on Rayleigh and SH waves. Next is a section on real-life implementation of guided wave for industrial problems. The paper, though briefly talks about the early development for completeness,. is primarily focussed on the recent progress made in the last decade. The paper ends by discussing and highlighting the future directions and open areas of research in guided wave based SHM.

https://iopscience.iop.org/article/10.1088/0964-1726/25/5/053001/pdf

Guided wave based structural health monitoring: A review

The detection of acoustic signals is of relevance for a range of practical applications, for example in medical diagnostics. However, whereas rectification of electric current and other energy forms such as thermal flux has been demonstrated, acoustic rectification has not yet been achieved. Here, on the basis of the earlier theoretical proposal of an 'acoustic diode', we present the first experimental demonstration of a rectified energy flux of acoustic waves. A one-dimensional acoustic rectifier is fabricated by coupling a superlattice with a layer of ultrasound contrast agent microbubble suspension. A significant rectifying effect is observed within two frequency bands at locations that agree well with theoretical predictions. Following optimization of the concentration of the microbubble suspension, rectifying ratios can be as high as ~10(4). This realization of an acoustic rectifier should have substantial practical significance, for example in the focusing of ultrasound in medical applications.

An acoustic rectifier

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

X-ray microcomputed tomography (microCT) has become an established method of testing and analyzing additively manufactured parts in recent years, being especially useful and accurate for d...

X-Ray microcomputed tomography in additive manufacturing : a review of the current technology and applications

Adhesive bonding is widely used in aerospace composite structures. A continuous well-cured bond can offer good joint strength and improved fatigue and impact resistance, and is therefore crucial to the performance of the entire structure. This paper explores the feasibility of using feature guided waves (FGW) for rapid screening of the bond line between a stiffener and a carbon fiber reinforced polymer (CFRP) composite panel. Such FGWs are capable of focusing the wave energy along the stiffener and the bond layer, with limited radiation to the adjacent plate. The Semi-Analytical Finite Element (SAFE) approach is employed to understand the modal properties of FGWs that exist in the structure, and criteria are suggested to choose proper mode-frequency combination that is sensitive to adhesive defects. A shear horizontal type FGW mode is identified to be well suited, as it is easy to excite, and propagates with little dispersion and relatively low attenuation, while it retains sufficient energy around the bond layer. Both 3D Finite Element (FE) simulations and experiments are performed to study the interaction of the selected FGW mode with defects in the adhesive bond, and the results show excellent agreement. The reflection behavior and the wave-defect resonance phenomenon are investigated, which demonstrate the capability of the FGW for the bond line inspection.

Feature guided wave inspection of bond line defects between a stiffener and a composite plate

Detection of damage in welded joints using high order feature guided ultrasonic waves

Focusing of ultrasonic waves in water plays an important role in various scenarios ranging from biomedical imaging to nondestructive testing. Acoustic metasurfaces have been largely explored for acoustic focusing, but they are generally narrowband and mainly implemented for airborne sound because of their structural complexity. Nevertheless, our previous development of metasurfaces provides a great opportunity to solve the challenges. Here, we present numerically and experimentally the broadband focusing of ultrasonic waves in water with a metasurface lens consisting of an array of deep-subwavelength sized and spaced slots. The slot widths of the metasurface are optimized based on microscopic coupled-wave theory. Due to the non-resonant arrangement, the focusing effect is demonstrated over a broad band of frequencies. The metasurface lens with simplicity and an ultra-compact size provides a feasible means for the design of thin and lightweight ultrasonic devices and is suitable for practical applications in biomedical and industrial fields.

Broadband ultrasonic focusing in water with an ultra-compact metasurface lens

Mechanical surface treatments are performed on aerospace components for fatigue life enhancement by introducing beneficial compressive stress profiles and material strengthening. This paper studies the influence of Deep Cold Rolling (DCR) on the residual stress distribution, work hardening and the microstructure modification of two nickel-based superalloys, IN100 and RR1000. Two different diameters (6.3 mm and 12.6 mm) of the rolling ball inserts were investigated in this analysis. The hardness and residual stresses at the subsurface after DCR were analyzed along the rolling and transverse directions. Electron BackScatter Diffraction (EBSD) technique was used to characterize the microstructure of the samples both qualitatively and quantitatively. The degree of work hardening of fine grain RR1000 after DCR was characterized using full width at half-maximum (FWHM) of the X-ray diffraction peaks and Grain Orientation Spread (GOS) profiles acquired by EBSD characterization. The results clearly indicate that deep cold rolling introduces compressive residual stresses as deep as 1 mm, with significant work hardening at the subsurface in the coarse grain IN100. DCR resulted in the grain refinement, increase in low angle grain boundaries and clustering of dislocation density around the carbides in IN100. Depending on the ball diameter, DCR of RR1000 induced compressive residual stresses up to 700 µm and work hardening till the depths of 400 µm. Additionally, severe deformation of grains occurred near the rolling surface. The larger diameter of the rolling ball resulted in high degree of work hardening and better residual stress distribution deeper into the materials.

/pdf/effect-of-deep-cold-rolling-on-mechanical-properties-and-1sqdr2eq8w.pdf

Effect of deep cold rolling on mechanical properties and microstructure of nickel-based superalloys

Guided waves propagating in lossy media are encountered in many problems across different areas of physics such as electromagnetism, elasticity and solid-state physics. They also constitute essential tools in several branches of engineering, aerospace and aircraft engineering, and structural health monitoring for instance. Waveguides also play a central role in many non-destructive evaluation applications. It is of paramount importance to accurately represent the material of the waveguide to obtain reliable and robust information about the guided waves that might be excited in the structure. A reasonable approximation to real solids is the perfectly elastic approach where the frictional losses within the solid are ignored. However, a more realistic approach is to represent the solid as a viscoelastic medium with attenuation for which the dispersion curves of the modes are, in general, different from their elastic counterparts. Existing methods are capable of calculating dispersion curves for attenuated modes but they can be troublesome to find and the solutions are not as reliable as in the perfectly elastic case. In this paper, in order to achieve robust and accurate results for viscoelasticity a spectral collocation method is developed to compute the dispersion curves in generally anisotropic viscoelastic media in flat and cylindrical geometry. Two of the most popular models to account for material damping, Kelvin–Voigt and Hysteretic, are used in various cases of interest. These include orthorhombic and triclinic materials in single- or multi-layered arrays. Also, and due to its importance in industry, a section is devoted to pipes filled with viscous fluids. The results are validated by comparison with those from semi-analytical finite-element simulations.

https://royalsocietypublishing.org/doi/pdf/10.1098/rspa.2015.0268

Zheng Fan

Papers

Feature guided wave inspection of bond line defects between a stiffener and a composite plate

Detection of damage in welded joints using high order feature guided ultrasonic waves

Broadband ultrasonic focusing in water with an ultra-compact metasurface lens

Effect of deep cold rolling on mechanical properties and microstructure of nickel-based superalloys

Guided waves' dispersion curves in anisotropic viscoelastic single- and multi-layered media