小原 良和
「先進超音波計測に関する萌芽技術研究会」は，「レーザ（非接触）超音波」に関する研究会と「非線形超音波」に関する研究会が，発展的に融合する形で発足した「超音波計測に関する萌芽技術研究会（主査：大阪大学 林高弘教授）」を引き継ぎ，2020 年6 月に発足しました。このタイミングはまさにコロナが始まった時期と重なったことから，活動期間2 年間の運営は，まさに試行錯誤の連続となりました。結果としては，対面はもとより，ハイブリッド開催もかないませんでしたが，幹事の先生方（愛媛大学中畑和之教授，東芝 山本摂様）をはじめ，委員の方々，講演者の方々の多大なご協力のおかげで，年間2 ～ 3 回開催した研究会では，毎回，大変多くの方々にご参加いただき，オンラインでも盛況に開催できましたことを，この場をお借りして厚く御礼申し上げます。
コロナ禍で日々の業務のオンライン化が大きく前進した感はありますが，本研究会でもこのオンラインの利点を生かして，対面であれば直接お越しいただくのは難しい海外の先生方にご講演をいただく機会も何度か実現することができました。海外研究者の講演をお伺いすると，コロナ禍で抑制された人流とは対照的に，NDE の世界潮流や最新研究の発展には著しいものがあり，その内容は，一度の研究会で留めるのは大変勿体ないと考え，今回，ヨーロッパを中心とした海外の先生方に解説記事のご執筆を依頼した次第です。
1つ目の解説記事は国際的にも注目の高いNDE 4.0 に関するものですが，これはNDE 4.0 に関する初の国際会議（International Conference on NDE 4.0）のオーガナイザーもつとめられ，エバンジェリストとしても活躍されているDr. Johannes Vrana とDr. Ripi Singh にご執筆いただきましたが，特に産業界における今後のNDE 分野の指針ともなり得る内容で，Digitalization やDX の定義から最近の成功例まで，大変示唆に富む内容となっております。2 つ目の解説記事は，非線形超音波による非破壊評価の世界的権威でもあるDr. Igor Solodov（ドイツ シュトゥットガルト大学）にLocal Defect Resonanceを用いた各種方法について，基礎理論・実験から実用化に向けた現場適用性向上の内容も含む形でご紹介いただいております。3 つ目の解説記事では，ガイド波を用いた全音場イメージング技術について，ポーランドの若手代表のDr. Łukasz Pieczonka（ポーランド AGH 科学技術大学）に，信号処理法，測定装置構成について，全体を網羅する形で分かりやすくご紹介いただいております。4 つ目の解説記事は，近年，複合材料の超音波非破壊評価の分野において極めてアクティビティの高い，まさに新進気鋭のDr. Mathias Kersemans（ベルギー ゲント大学）に，水浸超音波法をベースとして，独自の信号処理やスキャン技術を駆使した繊維強化複合材料の評価法についてご執筆いただいております。なお，今回は英語の解説記事ということで，各記事の最後に日本語の要約を付けさせて頂きました。本特集記事が読者の皆様の研究・開発・日々の業務に少しでもお役に立てば幸甚です。
末筆になりますが，コロナ禍で大変ご多忙な状況にもかかわらず，快くご執筆いただいた先生方，本特集号の企画から刊行まで，海外との英語でのやり取りも含めて，丁寧にご対応いただいた機関誌編集担当の皆様に，誌面をお借りして改めて御礼申し上げます。
Vrana GmbH Johannes VRANA
Inspiring Next Ripi SINGH
Abstract
Digital transformation is the most misused term in recent years in addition to being a popular sales buzzword.
Part of the confusion comes from it being a long journey with an ever-changing destination and new pathways emerging all the time.
All of us can only see a small fraction of the vast landscape based on our past experiences and current context, and yet believe it to be the universe.
Based on our worldview we fall in the trap of being right albeit incomplete.
In this paper, authors take a holistic view of the industrial society and demystify frequently used terms – digitization, digitalization, and digital transformation.
Then they discuss these three terms in context of NDE 4.0 with a few recently concluded success stories.
Each of these situations is a very tiny piece of the mega puzzle, we are all engaged in building.
In the end, authors allude to the need and a way to plan the digital transformation roadmap.
Key Words:NDE 4.0, Use cases, Value proposition, Future of NDE, NDT 4.0, Digitization, Digitalization, Digital Transformation
Introduction
Since 2018“ Welcome to the World of NDE 4.0” became the opening phrase for presentations and keynotes around the globe, for１）, and for the various presentations on the NDE 4.0 YouTube Channel２）.
NDE 4.0 is the ongoing fourth revolution of NDE (see Fig.1) and represents the confluence of the physical world of nondestructive evaluation and sensors with the world of emerging cyber technologies associated with Industry 4.0３）.
It is a world which will lead to the vital correction of the value perception of NDT and NDE by deriving value from the data in digital twins and cyber-physical loops４）.
However, it requires serious collaboration to build the necessary infrastructure５） for the digital transformation of the NDE eco-system６）.
NDE 4.0 and digital transformation in general are rather a journey t han your typical project.７）
offers a g uideline how to develop your roadmap towards NDE 4.0 and ８） gives serious background information on a variety of activities regarding NDE 4.0.
Institute for Polymer Technology, University of Stuttgart Igor SOLODOV and Marc KREUTZBRUCK
Abstract
The study is aimed at enhancing efficiency and sensitivity of acoustic NDT techniques by using the concept of a local resonance of defects. The novelty of the proposed approach is that it provides a selective acoustic excitation and energy delivery from the wave directly to the defect via its mechanical resonance. By frequency match between a probing elastic wave and the defect resonance, a substantial enhancement in efficiency and sensitivity of ultrasonic NDT techniques is validated. A significant improvement is demonstrated for the family of prospective ultrasound-activated effects (nonlinear, thermal, etc.) which are usually comparatively inefficient so that the corresponding NDT and imaging techniques require an elevated acoustic power and specific instrumentation adapted to high-power ultrasonics. The resonance and non-contact versions for nonlinear ultrasonics, ultrasonic thermography (thermosonics) and air-coupled acoustic emission with advanced efficiency are presented, which enable to avoid high-power apparatuses and use commercial low-energy equipment instead.
Key Words:Local defect resonance, Nonlinear NDT, Thermosonics, Resonant air-coupled emission
Introduction
Acoustic/ultrasonic methods based on the wave transmission and reflection by the defects is a well-established tool for detection and characterization of damage in NDT. The efficiency of an acoustic wave-defect interaction is an important factor, which determines sensitivity and eventually an applicability area of ultrasonic NDT-techniques. In the conventional acoustic inspection, a defect is considered as a passive scatterer while to enhance its response the wave frequency has to be selected high enough to overcome the diffraction limit defined by the ratio of the defect size and acoustic wavelength.
In our previous studies１）, a novel NDT methodology was proposed to enhance an acoustic response of a defect by using frequency-selective acoustic activation based on the concept of Local Defect Resonance (LDR). Under the frequency match condition between the driving wave and LDR, the input energy is delivered and trapped selectively in the defect area that increases dramatically its vibration amplitude. The LDR approach enhances substantially the efficiency of NDT techniques based on acoustic/vibration activation of damage (Vibro-thermography, Vibro-shearography, Nonlinear acoustics,etc.) and in recent years has generated much interest in development and applications of the LDR-based techniques for NDT and imaging of defects.
AGH University of Science and Technology Jakub SPYTEK and Łukasz PIECZONKA
Abstract
This paper presents state of the art in full-field damage characterization in plate-like structures with guided ultrasonic waves. We begin with recalling the basic theory of Lamb waves propagating in plates and discuss their interaction with damage. Subsequently, we discuss signal processing techniques used for damage evaluation, including the techniques based on local energy maps, wave scattering, mode conversions, and local wavenumber estimation. Next, we present the commonly used experimental methods for exciting and measuring Lamb waves propagating in plates. We conclude by outlining future prospects for applying guided waves for damage characterization in engineering applications.
Key Words:Guided waves, Nondestructive testing, Local wavenumber estimation, Laser vibrometry
Introduction
Elastic waves in the ultrasonic frequency range are commonly used in Nondestructive Testing (NDT) of engineered structures. The classical ultrasonic (US) inspection techniques involve using bulk ultrasonic waves (longitudinal and shear) that are emitted and received by contact ultrasonic probes. This type of inspection may operate in different configurations such as the pulse-echo, pitch-catch, or through-transmission and requires repositioning of US probes over a test sample to map internal defects１）. The presence of defects is determined from the analysis of linear wave features such as wave reflections or attenuation. The bulk wave techniques are well-established, relatively simple to apply, and can be adjusted to various problems and structures. Despite their many advantages, the classical US techniques also face challenges in specific applications. Detailed scans of large surface areas are timeconsuming, even when automated. In addition, maintaining proper acoustic coupling and alignment of the probes over the entire scan area may be challenging. Thin-walled samples may require double-sided access for a successful inspection. Therefore, alternative testing approaches for such scenarios are desired. Guided ultrasonic waves provide such alternative solution to inspect thin-walled, geometrically bounded structures, such as plates or pipes. Different types of guided waves can propagate in bounded plates, including surface waves (Rayleigh waves), Lamb waves, or shear-horizontal waves２）. Among them, Lamb waves are the most widely used for damage detection and monitoring３）, as they can propagate over long distances, are relatively easy to excite and measure, and exhibit sensitivity to various types of damage４）. The Lamb waves are governed by a set of Rayleigh-Lamb equations derived from general equations of waves propagating in elastic media２）.
Mechanics of Materials and Structures (UGent-MMS), Ghent University
Mathias KERSEMANS and Xiaoyu YANG
Wave Propagation and Signal Processing (WPSP), KU Leuven Campus Kulak Koen VAN DEN ABEELE
Mechanics of Materials and Structures (UGent-MMS), Ghent University Wim VAN PAEPEGEM
Abstract
This paper presents a concise overview of work performed at Ghent University, in collaboration with the University of Leuven, over the past ten years on the characterization of (damaged) composite laminates using water-coupled ultrasound testing in the frequency band of 5~15MHz. Focus is put on the determination of damage- and material parameters using either a conventional lateral surface scan or a rotational point scan:
i. Robust imaging of complex distributed defect clusters, e.g. barely visible impact damage, by fitting the instantaneous amplitude of recorded signals to a Rice distribution using maximum likelihood estimation.
ii. Reconstruction of the 3D volumetric fiber architecture by analyzing the instantaneous amplitude and phase of signals near the ply-resonance frequency with computed tomography methods.
iii. Characterization of the local orthotropic viscoelastic stiffness tensor by coupling angled ultrasound measurements with a forward analytical simulation model using heuristic inversion routines.
iv. Estimation of the local strain tensor, for surface-textured plates, by analysis of the backscattered ultrasound in the Bragg regime.
The general concept behind each of these applications is shortly introduced, followed by a numerical and/or experimental demonstration.
Key Words:Ultrasound, Composite, Damage, Fiber architecture, Orthotropic viscoelastic tensor, Strain tensor
Introduction
Fiber reinforced polymers (FRP), also commonly called composites, are increasingly being used in high-tech applications because of their high specific strength and stiffness, excellent chemical resistance and large design freedom. By optimizing the fiber orientation and ply layup, they can be tailored for specific structural applications. Yet, due to their inherent structural heterogeneity (at various scales), mechanical anisotropy and multi-layer structure, composite materials are susceptible to a variety of internal damage phenomena which may be introduced during either the manufacturing cycle or the operational lifetime. Examples of damage phenomena include matrix cracks, delamination, fiber wrinkling and waviness, fiber breakage, dry spots and barely visible impact damage (BVID). Hence, the development and application of nondestructive inspection methodologies are indispensable in order to verify their structural quality and to ascertain their envisaged mechanical performance.
This paper discusses some of the recent work performed at Ghent University and the University of Leuven on immersion ultrasonic inspection of composite laminates in order to accurately assess complex defect clusters, e.g. BVID (section 3.1), reconstruct the 3D volumetric fiber architecture (section 3.2), characterize the local viscoelastic orthotropic stiffness tensor (section 4.1) and determine the local strain tensor (section 4.2).
