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15 pages, 6530 KiB

Open AccessArticle

Influence of Artificial Soft Tissue on Intra-Operative Vibration Analysis Method for Primary Fixation Monitoring in Cementless Total Hip Arthroplasty

by George Athanassoulis Makris, Leonard Pastrav, Quentin Goossens, Maikel Timmermans, Michiel Mulier, Georges Frederic Vles, Wim Desmet and Kathleen Denis

Appl. Sci. 2022, 12(8), 4027; https://doi.org/10.3390/app12084027 - 15 Apr 2022

Cited by 1 | Viewed by 1592

Abstract

In cementless Total Hip Arthroplasty (THA), achieving high primary implant fixation is crucial for the long-term survivorship of the femoral stem. While orthopedic surgeons traditionally assess fixation based on their subjective judgement, novel vibration-analysis fixation-monitoring techniques show promising potential in providing the surgeon [...] Read more.

In cementless Total Hip Arthroplasty (THA), achieving high primary implant fixation is crucial for the long-term survivorship of the femoral stem. While orthopedic surgeons traditionally assess fixation based on their subjective judgement, novel vibration-analysis fixation-monitoring techniques show promising potential in providing the surgeon with objective and quantifiable fixation measurements. This study presents a dynamic response measurement protocol for implant endpoint insertion and evaluates this protocol in the presence of artificial soft tissue. After the artificial femur was prepared in accordance with the THA protocol, the implant was inserted and progressively hammered into the cavity. The Pearson Correlation Coefficient (PCC) and Frequency Response Assurance Criterion (FRAC) corresponding to each insertion hammer hit were derived from the Frequency Response Functions (FRF) corresponding to each insertion step. The protocol was repeated with the artificial femur submerged in artificial soft tissue to imitate the influence of anatomical soft tissue. The FRAC appeared overall more sensitive than the PCC. In the presence of the artificial soft tissue the technique yielded higher PCC and FRAC values earlier in the insertion process. The measurements with artificial soft tissue produced FRFs with fewer peaks, lower resonance frequencies, and overall higher damping factors. The soft tissue appears to limit the fixation-change detection capabilities of the system and a promising potential remedy to this limitation is suggested. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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16 pages, 2535 KiB

Open AccessArticle

An Open Access Chamber Designed for the Acoustic Characterisation of Microbubbles

by Elliott Smith, Luzhen Nie, James McLaughlan, Harry Clegg, Thomas Carpenter, David Cowell, Stephen Evans, Alejandro F. Frangi and Steven Freear

Appl. Sci. 2022, 12(4), 1818; https://doi.org/10.3390/app12041818 - 10 Feb 2022

Cited by 3 | Viewed by 1773

Abstract

Microbubbles are used as contrast agents in clinical ultrasound for Left Ventricular Opacification (LVO) and perfusion imaging. They are also the subject of promising research in therapeutics as a drug delivery mechanism or for sonoporation and co-administration. For maximum efficacy in these applications, [...] Read more.

Microbubbles are used as contrast agents in clinical ultrasound for Left Ventricular Opacification (LVO) and perfusion imaging. They are also the subject of promising research in therapeutics as a drug delivery mechanism or for sonoporation and co-administration. For maximum efficacy in these applications, it is important to understand the acoustic characteristics of the administered microbubbles. Despite this, there is significant variation in the experimental procedures and equipment used to measure the acoustic properties of microbubble populations. A chamber was designed to facilitate acoustic characterisation experiments and was manufactured using additive manufacturing techniques. The design has been released to allow wider uptake in the research community. The efficacy of the chamber for acoustic characterisation has been explored with an experiment to measure the scattering of SonoVue^® microbubbles at the fundamental frequency and second harmonic under interrogation from emissions in the frequency range of 1.6 to 6.4 MHz. The highest overall scattering values were measured at 1.6 MHz and decreased as the frequency increased, a result which is in agreement with previously published measurements. Statistical analysis of the acoustic scattering measurements have been performed and a significant difference, at the 5% significance level, was found between the samples containing contrast agent and the control sample containing only deionised water. These findings validate the proposed design for measuring the acoustic scattering characteristics of ultrasound contrast agents. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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12 pages, 4100 KiB

Open AccessArticle

Verification of 3D AE Source Location Technique in Triaxial Compression Tests Using Pencil Lead Break Sources on a Cylindrical Metal Specimen

by Xianfeng Li, Ali Naqi, Zain Maqsood and Junichi Koseki

Appl. Sci. 2022, 12(3), 1603; https://doi.org/10.3390/app12031603 - 02 Feb 2022

Cited by 2 | Viewed by 1258

Abstract

Recently, the acoustic emission (AE) technique has been widely applied in the field of geotechnical engineering. One of the main applications of this technique is to locate damage sources, which is known as the AE source location technique. In this research, the 3D [...] Read more.

Recently, the acoustic emission (AE) technique has been widely applied in the field of geotechnical engineering. One of the main applications of this technique is to locate damage sources, which is known as the AE source location technique. In this research, the 3D AE source location technique based on the time difference of arrival is verified by conducting pencil lead break (PLB) tests on a cylindrical metal specimen. From the results of this study, the existing method is proven to have the least error in terms of distance from the coordinate origin, but with some errors along x, y, and z axes. When the PLB sources originate in the middle part of the specimen, the calculated result has a higher accuracy, as compared to other positions. It seems that the calculated AE sources tend to be concentrated on the central part with some errors. Moreover, outside noises induced by a hammer hit have virtually no effect on this AE source location technique. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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14 pages, 5191 KiB

Open AccessArticle

Determination of Concrete Formwork Removal Time Based on Ultrasound Reflection

by Nicolas Ospitia, Rami Jaramani, Olivier Remy and Dimitrios G. Aggelis

Appl. Sci. 2022, 12(3), 1221; https://doi.org/10.3390/app12031221 - 24 Jan 2022

Cited by 2 | Viewed by 2840

Abstract

Concrete is vastly used in construction due to its high compressive strength, and its ease of shaping. Formworks are used to render the desired shape to the material during its change from a liquid to a solid state, until the concrete develops the [...] Read more.

Concrete is vastly used in construction due to its high compressive strength, and its ease of shaping. Formworks are used to render the desired shape to the material during its change from a liquid to a solid state, until the concrete develops the required strength. Removing the formwork early can cause excessive deformations or even failure; however, postponing removal also has a delaying effect in construction with economic consequences. In practice, the removal of the formworks is based on the development of the compressive strength vs. the self-weight and temporary loads related to the construction. This study aims to monitor the hardening of concrete columns by means of the reflection of ultrasonic waves. As concrete hardens, its mechanical impedance increases influencing the reflection that can be received by one-sided non-invasive measurements. By suitably selecting the stiffness of the ultrasonic buffer material, the moment that the concrete obtains a specific stiffness can be safely determined for the first time. Results demonstrate sensitivity of the technique on real scale formworks, as it can pinpoint the moment in which the formwork can be removed, while numerical simulations help in the understanding of the complicated wave field and validate the methodology. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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24 pages, 2903 KiB

Open AccessArticle

Application of Particle Dampers on a Scaled Wind Turbine Generator to Improve Low-Frequency Vibro-Acoustic Behavior

by Braj Bhushan Prasad, Fabian Duvigneau, Daniel Juhre and Elmar Woschke

Appl. Sci. 2022, 12(2), 671; https://doi.org/10.3390/app12020671 - 11 Jan 2022

Cited by 8 | Viewed by 1801

Abstract

The purpose of this paper is to introduce a honeycomb damping plate (HCDP) concept based on the particle damping technique to reduce the low-frequency vibration response of wind turbine generators. The HCDP cells contain granular materials and are mounted at different positions on [...] Read more.

The purpose of this paper is to introduce a honeycomb damping plate (HCDP) concept based on the particle damping technique to reduce the low-frequency vibration response of wind turbine generators. The HCDP cells contain granular materials and are mounted at different positions on the generator to reduce the transmission of vibrations from stator ring to stator arm. To investigate the efficiency of the HCDP concept in the laboratory, a small-scale replica inspired by the original wind turbine generator is used as reference geometry. The efficiency of the vibration attenuation by using the HCDP concept is experimentally investigated with the help of a laser scanning vibrometer device. In this contribution, the influence of four different granular materials on the vibration attenuation is experimentally investigated. Furthermore, the influence of HCDP positioning on the transmission path damping is analyzed. Apart from this, the effect of single-unit (SU) and multi-unit (MU) HCDP on the frequency response of the generator is also studied. The experimental approach in this paper shows good damping properties of the HCDP concept for reducing the vibration amplitude. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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13 pages, 4414 KiB

Open AccessArticle

Estimation of Acoustic Source Positioning Error Determined by One-Dimensional Linear Location Technique

by Artem Marchenkov, Igor Vasiliev, Dmitriy Chernov, Daria Zhgut, Daria Moskovskaya, Ivan Mishchenko and Ekaterina Kulikova

Appl. Sci. 2022, 12(1), 224; https://doi.org/10.3390/app12010224 - 27 Dec 2021

Cited by 1 | Viewed by 1873

Abstract

The one-dimensional (1D) linear location technique has been considered as one of the methods for determining the position of acoustic emission (AE) sources in metallic objects. However, this approach does not take into account the heterogeneity of materials and that leads to poor [...] Read more.

The one-dimensional (1D) linear location technique has been considered as one of the methods for determining the position of acoustic emission (AE) sources in metallic objects. However, this approach does not take into account the heterogeneity of materials and that leads to poor accuracy of AE sources localization. To estimate the positioning error of the linear location technique which is typically used to determine the AE source location a new approach based on the combination of experimental and simulation methods is proposed. This approach for error estimation contains a finite element model construction of the AE signals localization. The model consists of transmitting and receiving transducers mounted on the test object, the frequency response of which selected close to the characteristics of acoustic emission transducers applied in the preliminary experiments. The application of the approach in current research showed that a reduced positioning error on a flat steel plate reaches 15%. The proposed technique can be used to optimize the number of preliminary tests required to calculate the reduced error of the 1D linear location technique applied for the AE sources localization during the inspection of the structure. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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12 pages, 4058 KiB

Open AccessArticle

Exploiting Modern Chladni Plates to Analogously Manifest the Point Interaction

by Yu-Chen Tseng, Yu-Hsin Hsu, Yu-Hsiang Lai, Yan-Ting Yu, Hsing-Chih Liang, Kai-Feng Huang and Yung-Fu Chen

Appl. Sci. 2021, 11(21), 10094; https://doi.org/10.3390/app112110094 - 28 Oct 2021

Cited by 3 | Viewed by 6998

Abstract

A truncated basis is employed to analyze the influence of the point interaction on the eigenvalues and eigenfunctions in quantum billiards. The point interaction is numerically confirmed to cause the shift in the eigenvalue that leads the original eigenfunctions to be superposed to [...] Read more.

A truncated basis is employed to analyze the influence of the point interaction on the eigenvalues and eigenfunctions in quantum billiards. The point interaction is numerically confirmed to cause the shift in the eigenvalue that leads the original eigenfunctions to be superposed to form the new eigenfunction. The amplitude and nodal-line patterns of the eigenfunctions are found to vary significantly with the coupling strength. It is further verified that the point-driven Chladni plates can be employed to analogously manifest the noticeable dependence of the nodal-line pattern on the coupling strength. More importantly, the dispersion relation between the frequency and the wave number for the flexural wave can be precisely determined in the process of utilizing the point interaction to model the modern Chladni plates. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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21 pages, 71374 KiB

Open AccessArticle

Experimental Study of a Piezoelectric De-Icing System Implemented to Rotorcraft Blades

by Eric Villeneuve, Sebastian Ghinet and Christophe Volat

Appl. Sci. 2021, 11(21), 9869; https://doi.org/10.3390/app11219869 - 22 Oct 2021

Cited by 19 | Viewed by 2027

Abstract

A four-year project investigating the use of piezoelectric actuators as a vibration-based low power de-icing system has been initiated at the Anti-Icing Materials Laboratory. The work done preceding this investigation consisted of studying, numerically and experimentally, the system integration to a flat plate [...] Read more.

A four-year project investigating the use of piezoelectric actuators as a vibration-based low power de-icing system has been initiated at the Anti-Icing Materials Laboratory. The work done preceding this investigation consisted of studying, numerically and experimentally, the system integration to a flat plate structure, the optimal excitation of the system, the resonant structural modes and the shear stress amplitudes to achieve de-icing for that structure. In this new investigation, the concepts and conclusions obtained on the flat plate structure were used to design and integrate the system into a rotating blade structure. An experimental setup was built for de-icing tests in rotation within an icing wind tunnel, and a finite-element numerical model adapted to the new geometry of the blade was developed based on the expertise accumulated using previous flat plate structure analysis. Complete de-icing of the structure was obtained in the wind tunnel using the developed de-icing system, and its power consumption was estimated. The power consumption was observed to be lower than the currently used electrothermal systems. The finite-elements numerical model was therefore used to study the case of a full-scale tail rotor blade and showed that the power reduction of the system could be significantly higher for a longer blade, confirming, therefore, the relevance of further de-icing investigations on a full-scale tail rotor. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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14 pages, 5445 KiB

Open AccessArticle

Identification for Abutment Stress by Drilling Cuttings

by Jian Tan, Yunliang Tan, Zihui Wang and Yubao Zhang

Appl. Sci. 2021, 11(20), 9467; https://doi.org/10.3390/app11209467 - 12 Oct 2021

Cited by 2 | Viewed by 1141

Abstract

The concentration of abutment pressure acting on coal seams induced by mining is a key factor to trigger rock burst. Understanding of abutment pressure or stress concentration is fundamental in preventing and controlling rock burst. The influence on abutment pressure fluctuation caused by [...] Read more.

The concentration of abutment pressure acting on coal seams induced by mining is a key factor to trigger rock burst. Understanding of abutment pressure or stress concentration is fundamental in preventing and controlling rock burst. The influence on abutment pressure fluctuation caused by the inhomogeneity of coal seams needs to be considered, but it is difficult to obtain by the present usual ways such as acoustic transmission, electromagnetic wave transmission, etc. In this article, the relationship between the amount of cuttings drilled in a coal seam and stress level was analyzed by considering the effect of drilling cutting expansion, and the drilling cutting test was carried out in Xinglongzhuang Coal Mine, Shandong Energy Ltd. It is found that the amount of cuttings drilled is positively related to the degree of stress concentration in both the plastic fracture zone and elastic zone. The amount of drilling cuttings is closely related to the roof weighting. In addition, the irregular fluctuation of drilling cuttings is an approximate map of distribution of stress concentration because of the non-uniformity of cracks and other defects in the coal seam. In order to meet the need of rock burst prevention by accurate pressure relief in high-stress zones, enough boreholes are needed. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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18 pages, 6305 KiB

Open AccessArticle

Elastic Properties Estimation of Masonry Walls through the Propagation of Elastic Waves: An Experimental Investigation

by Jacopo Marazzani, Nicola Cavalagli and Vittorio Gusella

Appl. Sci. 2021, 11(19), 9091; https://doi.org/10.3390/app11199091 - 29 Sep 2021

Cited by 8 | Viewed by 1836

Abstract

Structural identification is one of the most important steps when dealing with historic buildings. Knowledge of the parameters, which define the mechanical properties of these kinds of structures, is fundamental in preparing interventions aimed at their restoration and strengthening, especially if they have [...] Read more.

Structural identification is one of the most important steps when dealing with historic buildings. Knowledge of the parameters, which define the mechanical properties of these kinds of structures, is fundamental in preparing interventions aimed at their restoration and strengthening, especially if they have suffered damage due to strong events. In particular, by using non-destructive techniques it is possible to estimate the mechanical characteristics of load-bearing structures without compromising the artistic value of the monumental buildings. In this paper, after recalling the main theoretical aspects, the use of elastic waves propagation through impact tests for the characterization of the masonry walls of a monumental building is described. The impact test allowed us to estimate the elastic characteristics of the homogeneous solid equivalent to masonry material. This confirms the great potential of the non-destructive diagnostics suitable for analyzing important structural parameters without affecting the preservation of historical masonry structures. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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15 pages, 20880 KiB

Open AccessArticle

Estimation of the Frequency Response Function of the Rotational Degree of Freedom

by Ji-wook Kim, Jae-wook Lee, Kun-woo Kim, Ji-heon Kang, Min-seok Yang, Dong-yul Kim, Seung-yeop Lee and Jin-seok Jang

Appl. Sci. 2021, 11(18), 8527; https://doi.org/10.3390/app11188527 - 14 Sep 2021

Cited by 3 | Viewed by 1578

Abstract

One of the factors that influence the dynamic characteristics of machining systems is the cutting tool. Cutting tools are very diverse, and receptance coupling substructure analysis (RCSA) is essential for analyzing the dynamic characteristics of each tool. For RCSA, a full receptance matrix [...] Read more.

One of the factors that influence the dynamic characteristics of machining systems is the cutting tool. Cutting tools are very diverse, and receptance coupling substructure analysis (RCSA) is essential for analyzing the dynamic characteristics of each tool. For RCSA, a full receptance matrix of the equipment and tools is essential. In this study, rotational degree-of-freedom receptance was estimated and analyzed using translational receptance. Displacement/moment receptance was analyzed according to the distance of the response point using the first-and second-order finite difference methods. The rotation/moment receptance was estimated according to the distance of the response point. Rotation/moment receptance was analyzed using Schmitz’s method and compensation strategies. The limitations of these strategies were analyzed, and the rotation/moment receptance for the beam under free-free boundary conditions was predicted using the second compensation strategy. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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16 pages, 5429 KiB

Open AccessFeature PaperArticle

Vibration Actuator System with Small-Scale Size Capable of Visual Inspection of Large Complex Iron Structures

by Hiroyuki Yaguchi and Yusuke Itoh

Appl. Sci. 2021, 11(16), 7467; https://doi.org/10.3390/app11167467 - 14 Aug 2021

Cited by 2 | Viewed by 1824

Abstract

Deterioration of social infrastructure equipment has become a major problem in countries around the world. In the present study, a novel vibration actuator system capable of movement on an iron structure having complicated surfaces, such as steps, is proposed. A vibration actuator capable [...] Read more.

Deterioration of social infrastructure equipment has become a major problem in countries around the world. In the present study, a novel vibration actuator system capable of movement on an iron structure having complicated surfaces, such as steps, is proposed. A vibration actuator capable of reciprocating movement with a small-scale size was prototyped and tested. In consideration of mobility, the size of the vibration actuator is designed to be smaller than 50 mm and the total mass is lighter than 20 g. The experimental result demonstrates that the maximum efficiency of the vibration actuator was 28.1%, and the maximum pulling power was 1.8 N. Furthermore, a vibration actuator system in which two vibration actuators and a wheel having a magnetic force connected by a flexible silicone rubber material was prototyped. This actuator system can move over a step of 48 mm in the horizontal plane and 25 mm in the vertical plane without control. Finally, a machine test was conducted on the frame surface moving, which is difficult even for robots. This actuator system can move at an average speed of 12.1 mm/s within the frame. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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14 pages, 22449 KiB

Open AccessArticle

Development of Folded Expanded Metal Mesh with Sound Absorption Performance

by Jui-Yen Lin, Yaw-Shyan Tsay and Pin-Chieh Tseng

Appl. Sci. 2021, 11(15), 7021; https://doi.org/10.3390/app11157021 - 29 Jul 2021

Cited by 2 | Viewed by 1928

Abstract

Reverberation time (RT) is an important factor affecting the quality of indoor acoustics. Using sound-absorbing materials is one method for quickly and effectively controlling RT, and installation in the ceiling is a common location. Sound-absorbing ceilings come in many forms, with light steel [...] Read more.

Reverberation time (RT) is an important factor affecting the quality of indoor acoustics. Using sound-absorbing materials is one method for quickly and effectively controlling RT, and installation in the ceiling is a common location. Sound-absorbing ceilings come in many forms, with light steel joist ceilings commonly used in office spaces, classrooms, and discussion rooms. Light steel joist ceilings are often matched with sound-absorbing materials such as gypsum board, mineral fiberboard, rock wool, and coated glass wool, but such materials may have durability and exfoliation problems. Therefore, considering performance and health, in this research, we aimed to design an expanded metal mesh (EMM) structure specimen for sound-absorption material, namely folded expanded metal mesh (FEMM). The results show that the FEMM can significantly improve the sound-absorption performance of the expanded metal mesh. The

α_{w}

of single panel is 0.05–0.35, and the

α_{w}

of FEMM is 0.65–0.85. On the other hand, the sound-absorption performance of the full frequency band has been significantly improved. Furthermore, the field validation result shows that RT decreased from 1.05–0.56 s at 500 Hz, meanwhile, the sound pressure level (SPL) is still evenly distributed, and speech clarity (C₅₀) is increased by 5.6–6.5. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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27 pages, 6891 KiB

Open AccessFeature PaperArticle

Detection and Localization of Multiple Damages through Entropy in Information Theory

by Rosario Ceravolo, Marco Civera, Erica Lenticchia, Gaetano Miraglia and Cecilia Surace

Appl. Sci. 2021, 11(13), 5773; https://doi.org/10.3390/app11135773 - 22 Jun 2021

Cited by 17 | Viewed by 3374

Abstract

According to recent works, entropy measures, and more specifically, spectral entropies, are emerging as an efficient method for the damage assessment of both mechanical systems and civil structures. Specifically, the occurrence of structural system alterations (intended in this work as stiffness reduction) can [...] Read more.

According to recent works, entropy measures, and more specifically, spectral entropies, are emerging as an efficient method for the damage assessment of both mechanical systems and civil structures. Specifically, the occurrence of structural system alterations (intended in this work as stiffness reduction) can be detected as a localized change in the signal entropy. Here, the Wiener Entropy (also known as the Spectral Flatness) of strain measurements is proved as a viable tool for single and multiple damage assessment, including damage detection, localization, and severity assessment. A case study from oil & gas engineering, i.e., a finite element model of a buried steel pipeline, is utilized for this aim. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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13 pages, 4047 KiB

Open AccessArticle

Computational Modeling of Ultrasound C-Scan Imaging Using Transmitted Signal Peak Density

by Koushik Paul, Jeremy Stromer, Samuel Razmi, Barbara A. Pockaj, Leila Ladani and Jafar Razmi

Appl. Sci. 2021, 11(11), 4924; https://doi.org/10.3390/app11114924 - 27 May 2021

Cited by 5 | Viewed by 1881

Abstract

Ultrasound measurement is a relatively inexpensive and commonly used imaging tool in the health sector. The through-transmission process of ultrasound measurement has been extensively evaluated for detecting abnormalities in tissue pathology. Compared to standard imaging parameters such as amplitude and time of flight, [...] Read more.

Ultrasound measurement is a relatively inexpensive and commonly used imaging tool in the health sector. The through-transmission process of ultrasound measurement has been extensively evaluated for detecting abnormalities in tissue pathology. Compared to standard imaging parameters such as amplitude and time of flight, quantitative ultrasound parameters in the frequency domain can provide additional details regarding tissue microstructures. In this study, pressure magnitude or amplitude variation in the frequency spectrum of the received signal was evaluated as a potential imaging technique using the spectral peak density parameter. Computational C-scan imaging analysis was developed through a finite element model. The magnitude variation in the received signal showed different patterns while interacting with and without inclusions. Images were reconstructed based on peak density values that varied with the presence of solid structure. The computational results were verified with the experimental C-scan imaging results from the literature. It was found that magnitude variation can be an effective parameter for C-scan imaging of thin structures. The feasibility of the study was further extended to identify the structure’s relative position along with the sample depth during C-scan imaging. While moving the structure in the direction of the sample depth, the pressure magnitude variation strongly followed a second-degree polynomial trend. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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19 pages, 4502 KiB

Open AccessArticle

Transmission Phase Control of Annular Array Transducers for Efficient Second Harmonic Generation in the Presence of a Stress-Free Boundary

by Hyunjo Jeong and Hyojeong Shin

Appl. Sci. 2021, 11(11), 4836; https://doi.org/10.3390/app11114836 - 25 May 2021

Cited by 2 | Viewed by 1481

Abstract

The through-transmission (TT) method is mainly used to measure the amplitude of the second harmonic from which the acoustic nonlinear parameter is determined for early damage detection of materials. The pulse echo (PE) method, however, has been excluded from nonlinear studies of solid [...] Read more.

The through-transmission (TT) method is mainly used to measure the amplitude of the second harmonic from which the acoustic nonlinear parameter is determined for early damage detection of materials. The pulse echo (PE) method, however, has been excluded from nonlinear studies of solid materials because the stress-free boundary suppresses the generation of second harmonics. It is more demanding to develop the PE method for practical applications and this paper considers a novel phase shift technique of annular array transducers to improve second harmonic generation (SHG) at the stress-free boundary. The fundamental and second harmonic fields after phase-shifted radiation are calculated, and their received amplitudes are investigated. The phase difference between the two second harmonic components after reflection from the stress-free boundary is analyzed to explain the enhanced SHG. The PE method with optimal phase shift can generate an improved second harmonic amplitude as high as about 45% of the TT method. Four element array transducers are also found to be more efficient in improved SHG than two element transducers. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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21 pages, 9806 KiB

Open AccessFeature PaperArticle

Study of Static and Dynamic Properties of Sand under Low Stress Compression

by Vladimir Frid, Stelios M. Potirakis and Semen Shulov

Appl. Sci. 2021, 11(8), 3311; https://doi.org/10.3390/app11083311 - 07 Apr 2021

Cited by 6 | Viewed by 1604

Abstract

The aim of this work was to investigate a wide range of grain sizes of sand in the pre-yield regime during compression through the combined study of ultrasound (US) wave speed and acoustic emission (AE). The specific study was performed using modified oedometer [...] Read more.

The aim of this work was to investigate a wide range of grain sizes of sand in the pre-yield regime during compression through the combined study of ultrasound (US) wave speed and acoustic emission (AE). The specific study was performed using modified oedometer and uniaxial compression experimental set-ups. The studied samples were natural dune sand (poorly graded on the poorly graded sand (SP) index) as well as its three extracted fractions as follows: 2.36–0.6 mm, 0.6–0.3 mm and 0.3–0.075 mm. The maximum compression stress during the modified oedometer experiments was <150 kPa, while during the modified uniaxial compression experiments, it was <400 kPa. Each sample was loaded while measuring the US pressure (P) wave speed and AE at each loading stage. The results show that the stiffer the soil is, the higher the value of the P wave speed measured, resulting in similar P wave velocity values achieved at a much lower applied stress during the oedometer experiments in comparison with the uniaxial compression tests. Regarding the AE results, it is seen that the higher the stress level is, causing more friction between the sand particles, the more AE events there are during their movement. The following parameters of AE were shown to be the most sensitive to the stress increase: the number of AE hits and the signals’ energy. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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21 pages, 6514 KiB

Open AccessArticle

Modal Analysis of the Lysozyme Protein Considering All-Atom and Coarse-Grained Finite Element Models

by Gustavo Giordani, Domenico Scaramozzino, Ignacio Iturrioz, Giuseppe Lacidogna and Alberto Carpinteri

Appl. Sci. 2021, 11(2), 547; https://doi.org/10.3390/app11020547 - 08 Jan 2021

Cited by 3 | Viewed by 2933

Abstract

Proteins are the fundamental entities of several organic activities. They are essential for a broad range of tasks in a way that their shapes and folding processes are crucial to achieving proper biological functions. Low-frequency modes, generally associated with collective movements at terahertz [...] Read more.

Proteins are the fundamental entities of several organic activities. They are essential for a broad range of tasks in a way that their shapes and folding processes are crucial to achieving proper biological functions. Low-frequency modes, generally associated with collective movements at terahertz (THz) and sub-terahertz frequencies, have been appointed as critical for the conformational processes of many proteins. Dynamic simulations, such as molecular dynamics, are vastly applied by biochemical researchers in this field. However, in the last years, proposals that define the protein as a simplified elastic macrostructure have shown appealing results when dealing with this type of problem. In this context, modal analysis based on different modelization techniques, i.e., considering both an all-atom (AA) and coarse-grained (CG) representation, is proposed to analyze the hen egg-white lysozyme. This work presents new considerations and conclusions compared to previous analyses. Experimental values for the B-factor, considering all the heavy atoms or only one representative point per amino acid, are used to evaluate the validity of the numerical solutions. In general terms, this comparison allows the assessment of the regional flexibility of the protein. Besides, the low computational requirements make this approach a quick method to extract the protein’s dynamic properties under scrutiny. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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14 pages, 4468 KiB

Open AccessArticle

Multiparameter Approach for Damage Propagation Analysis in Fiber-Reinforced Polymer Composites

by Claudia Barile, Caterina Casavola, Giovanni Pappalettera and Paramsamy Kannan Vimalathithan

Appl. Sci. 2021, 11(1), 393; https://doi.org/10.3390/app11010393 - 03 Jan 2021

Cited by 10 | Viewed by 1857

Abstract

Assessing the damage evolution in carbon-fiber-reinforced polymer (CFRP) composites is an intricate task due to their complex mechanical responses. The acoustic emission technique (AE) is a non-destructive evaluation tool that is based on the recording of sound waves generated inside the material as [...] Read more.

Assessing the damage evolution in carbon-fiber-reinforced polymer (CFRP) composites is an intricate task due to their complex mechanical responses. The acoustic emission technique (AE) is a non-destructive evaluation tool that is based on the recording of sound waves generated inside the material as a consequence of the presence of active defects. Proper analysis of the recorded waves can be used for monitoring the damage evolution in many materials, including composites. The acoustic track associated with the entire loading history of the sample or the structures is usually followed by using some descriptors, such as the amplitude of the sound waves and the number of counts. In this study, the acoustic emission in CFRP single-lap shear joints was monitored by using a multiparameter approach based on the contemporary analysis of multiple features, such as the absolute signal level (ASL), initiation frequency, and reverberation frequency, to understand whether a proper combination of them can be adopted for a more robust description of the damage propagation in CFRP structures. For selecting the best features, principal component analysis (PCA) was used. The selected features were classified into different clusters using fuzzy c-means (FCM) data clustering for analyzing the damage modes. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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Acoustic Emission Spectroscopy: Applications in Geomaterials and Related Materials

by Ekhard K. H. Salje, Xiang Jiang, Jack Eckstein and Lei Wang

Appl. Sci. 2021, 11(19), 8801; https://doi.org/10.3390/app11198801 - 22 Sep 2021

Cited by 9 | Viewed by 2514

Abstract

As a non-destructive testing technology with fast response and high resolution, acoustic emission is widely used in material monitoring. The material deforms under stress and releases elastic waves. The wave signals are received by piezoelectric sensors and converted into electrical signals for rapid [...] Read more.

As a non-destructive testing technology with fast response and high resolution, acoustic emission is widely used in material monitoring. The material deforms under stress and releases elastic waves. The wave signals are received by piezoelectric sensors and converted into electrical signals for rapid storage and analysis. Although the acoustic emission signal is not the original stress signal inside the material, the typical statistical distributions of acoustic emission energy and waiting time between signals are not affected by signal conversion. In this review, we first introduce acoustic emission technology and its main parameters. Then, the relationship between the exponents of power law distributed AE signals and material failure state is reviewed. The change of distribution exponent reflects the transition of the material’s internal failure from a random and uncorrelated state to an interrelated state, and this change can act as an early warning of material failure. The failure process of materials is often not a single mechanism, and the interaction of multiple mechanisms can be reflected in the probability density distribution of the AE energy. A large number of examples, including acoustic emission analysis of biocemented geological materials, hydroxyapatite (human teeth), sandstone creep, granite, and sugar lumps are introduced. Finally, some supplementary discussions are made on the applicability of Båth’s law. Full article

(This article belongs to the Special Issue Acoustics and Vibrations Analyses of Materials at Different Scales: Experimental and Numerical Approaches)

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