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  • MDPI AG  (10)
  • 1
    Online Resource
    Online Resource
    Localization and Imaging of Micro-Cracks Using Nonlinear Lamb Waves with Imperfect Group-Velocity Matching
    MDPI AG ; 2021
    In:  Applied Sciences Vol. 11, No. 17 ( 2021-08-31), p. 8069-
    Details
    In: Applied Sciences, MDPI AG, Vol. 11, No. 17 ( 2021-08-31), p. 8069-
    Abstract: Nonlinear Lamb waves have attracted increasing attention for detecting and identifying microstructural changes in structural health monitoring. However, most identification methods that determine the damage locations based on the intersections of the elliptical loci will inevitably cause positioning errors due to the change of the group velocity before and after interaction with the damage. In this work, a method focusing on elliptical rings was proposed for localization and imaging of micro-cracks in a three-dimensional structure using nonlinear Lamb waves with imperfect group-velocity matching. The width of the elliptical rings can be determined by the degree of the group-velocity mismatching of nonlinear S0 modes. The mode pair S0-s0, satisfying approximate group-velocity matching, is mainly introduced by interacting with the micro-crack. The effectiveness of the proposed methodology for damage localization is verified by the experimental testing and numerical simulation. Although the length of the being-tested small crack (about 1 mm) is smaller than the wavelength of the incident fundamental Lamb wave (around 20 mm), it can be well identified and localized using nonlinear Lamb waves. The experimental results show that the proposed method enables more reliable localization of the small crack with the crossover areas, as compared with the intersections based on the ellipse method. Furthermore, a breathing crack not situated in the propagation path can also be well localized by the proposed method in comparison with those by the probability-based diagnostic imaging in the simulation cases.
    Type of Medium: Online Resource
    ISSN: 2076-3417
    URL: Article
    DOI: 10.3390/app11178069
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2704225-X
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  • 2
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    Online Resource
    Damage Orientation and Depth Effect on the Guided Wave Propagation Behavior in 30CrMo Steel Curved Plates
    MDPI AG ; 2020
    In:  Sensors Vol. 20, No. 3 ( 2020-02-05), p. 849-
    Details
    In: Sensors, MDPI AG, Vol. 20, No. 3 ( 2020-02-05), p. 849-
    Abstract: In this paper, the guided wave propagation behavior in damaged 30CrMo steel curved plates was investigated experimentally and numerically. The effects of the notch orientation, depth in the curved plate, as well as its radius, on the wave propagation characteristics were mainly analyzed by the amplitude distribution curves and the directivity diagrams of A0/S0 (zero-th order of the symmetric/antisymmetric Lamb wave) modes. An ellipse-based algorithm was compiled to locate the notches in the curved plates. Results show that the normalized S0 wave amplitude in the circumferential orientation was the largest, and it increases as notch depth increases in the axial orientation. The A0 wave amplitude in axial orientation was the largest, while it decreases with the increasing of notch depth in the other orientations. The normalized A0 wave amplitude in axial orientation increases with the increasing of radius. With the increasing of radius, the other normalized A0/S0 amplitudes linearly decreased for the other paths. The ellipse-based algorithm has high notch localization accuracy, and the notch localization error increase from 0.005% to 1.47% with the notch depth decreasing from 5 mm to 1 mm in the curved plates. For the curved plates with different radius, the maximum notch localization error is 1.20%. These satisfactory results demonstrate the effectiveness of the developed algorithm in locating damages in the researched structure.
    Type of Medium: Online Resource
    ISSN: 1424-8220
    URL: Article
    DOI: 10.3390/s20030849
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
    detail.hit.zdb_id: 2052857-7
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  • 3
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    In-Situ Monitoring of a Filament Wound Pressure Vessel by the MWCNT Sensor under Hydraulic Fatigue Cycling and Pressurization
    MDPI AG ; 2019
    In:  Sensors Vol. 19, No. 6 ( 2019-03-21), p. 1396-
    Details
    In: Sensors, MDPI AG, Vol. 19, No. 6 ( 2019-03-21), p. 1396-
    Abstract: As a result of the high specific strength/stiffness to mass ratio, filament wound composite pressure vessels are extensively used to contain gas or fluid under pressure. The ability to in-situ monitor the composite pressure vessels for possible damage is important for high-pressure medium storage industries. This paper describes an in-situ monitoring method to permanently monitor composite pressure vessels for their structural integrity. The sensor is made of a multi-walled carbon nanotube (MWCNT) that can be embedded in the composite skin of the pressure vessels. The sensing ability of the sensor is firstly evaluated in various mechanical tests, and in-situ monitoring experiments of a full-scale composite pressure vessel during hydraulic fatigue cycling and pressurization are performed. The monitoring results of the MWCNT sensor are compared with the strains measured by the strain gauges. The results show that the measured signal by the developed sensor matches the mechanical behavior of the composite laminates under various load conditions. In the hydraulic fatigue test, the relationship between the resistance and the strain is built, and could be used to quantitative monitor the filament wound pressure vessel. The bursting of the pressure vessel can be detected by the sharp increase of the MWCNT sensor resistance. Embedding the MWCNT sensor into the composite pressure vessel is successfully demonstrated as a promising method for structural health monitoring.
    Type of Medium: Online Resource
    ISSN: 1424-8220
    URL: Article
    DOI: 10.3390/s19061396
    Language: English
    Publisher: MDPI AG
    Publication Date: 2019
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  • 4
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    Online Resource
    A Lorentz Force EMAT Design with Racetrack Coil and Periodic Permanent Magnets for Selective Enhancement of Ultrasonic Lamb Wave Generation
    MDPI AG ; 2022
    In:  Sensors Vol. 23, No. 1 ( 2022-12-22), p. 96-
    Details
    In: Sensors, MDPI AG, Vol. 23, No. 1 ( 2022-12-22), p. 96-
    Abstract: This article proposes an electromagnetic acoustic transducer (EMAT) for selectively improving the purity and amplitude of ultrasonic Lamb waves in non-ferromagnetic plates. The developed EMAT consists of a racetrack coil and a group of periodic permanent magnets (PPMs). Two-dimensional finite element simulations and experiments are implemented to analyze the working mechanism and performance of the PPM EMAT. Thanks to the specific design, the eddy currents increase with increasing wire density and the directions of the magnetic fields and Lorentz forces alternate according to the polarities of the magnet units. Wires laid uniformly beneath the magnets, and the gaps between adjacent magnets generate tangential and normal Lorentz forces, resulting in-plane (IP) and out-of-plane (OP) displacements, respectively. The constructive interference occurs when the wavelength of the generated Lamb wave is twice the spacing of the magnets, leading to large amplitudes of the targeted ultrasonic Lamb waves. Therefore, the PPM EMAT is capable of generating pure symmetric or antisymmetric mode Lamb waves at respective frequencies. The results prove that the developed PPM EMAT can generate pure either S0 or A0 mode Lamb waves at respective frequencies. The increase in wire width and wire density further increases the signal amplitudes. Compared with the case of conventional meander-line-coil (MLC) EMAT, the amplitudes of the A0 and S0 mode Lamb waves of our PPM EMAT are increased to 880% and 328%, respectively.
    Type of Medium: Online Resource
    ISSN: 1424-8220
    URL: Article
    DOI: 10.3390/s23010096
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
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  • 5
    Online Resource
    Online Resource
    Incidence and Simple Prediction Model of Hyperuricemia for Urban Han Chinese Adults: A Prospective Cohort Study
    MDPI AG ; 2017
    In:  International Journal of Environmental Research and Public Health Vol. 14, No. 1 ( 2017-01-11), p. 67-
    Details
    In: International Journal of Environmental Research and Public Health, MDPI AG, Vol. 14, No. 1 ( 2017-01-11), p. 67-
    Type of Medium: Online Resource
    ISSN: 1660-4601
    URL: Article
    DOI: 10.3390/ijerph14010067
    Language: English
    Publisher: MDPI AG
    Publication Date: 2017
    detail.hit.zdb_id: 2175195-X
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  • 6
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    Lamb Wave-Based Structural Health Monitoring on Composite Bolted Joints under Tensile Load
    MDPI AG ; 2017
    In:  Materials Vol. 10, No. 6 ( 2017-06-14), p. 652-
    Details
    In: Materials, MDPI AG, Vol. 10, No. 6 ( 2017-06-14), p. 652-
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma10060652
    Language: English
    Publisher: MDPI AG
    Publication Date: 2017
    detail.hit.zdb_id: 2487261-1
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  • 7
    Online Resource
    Online Resource
    Fatigue Damage Evaluation Using Nonlinear Lamb Waves with Quasi Phase-Velocity Matching at Low Frequency
    MDPI AG ; 2018
    In:  Materials Vol. 11, No. 10 ( 2018-10-09), p. 1920-
    Details
    In: Materials, MDPI AG, Vol. 11, No. 10 ( 2018-10-09), p. 1920-
    Abstract: Due to the dispersive and multimode natures, only nonlinear Lamb waves with exact phase-velocity matching were generally used in previous studies to evaluate the evenly distributed microstructural evolution in the incipient stage of material degradation, because of the cumulative generation of second harmonics, which was also found within a significant propagation distance for mode pair S0-s0 with quasi phase-velocity matching at low frequency. To explore the feasibility of fatigue damage evaluation by using this mode pair and fully utilize its unique merits, the cumulative second harmonic analysis was performed on aluminum alloy specimens with various material damage produced by the continuous low cycle fatigue tests. Similar to mode pair S1-s2 with exact phase-velocity matching, a mountain shape curve between the normalized acoustic nonlinearity parameter and the fatigue life was also achieved with the peak point at about 0.65 fatigue life for mode pair S0-s0, even though a relatively higher sensitivity to fatigue damage was observed for mode pair S1-s2. The excited frequency selection was further analyzed in a certain frequency range, where the quasi phase-velocity matching condition was satisfied for mode pair S0-s0 owing to the less dispersive property. Results show that the fatigue damage can be effectively detected using the mode pair S0-s0, and a relatively lower excited frequency was preferred due to its higher sensitivity to microstructural evolution.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma11101920
    Language: English
    Publisher: MDPI AG
    Publication Date: 2018
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  • 8
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    Characterization of Local Residual Stress at Blade Surfaces by the V(z) Curve Technique
    MDPI AG ; 2018
    In:  Metals Vol. 8, No. 8 ( 2018-08-19), p. 651-
    Details
    In: Metals, MDPI AG, Vol. 8, No. 8 ( 2018-08-19), p. 651-
    Abstract: The characterization of residual stress in complicated components is a tough issue. The method of Rayleigh surface wave-based V(z) curve is adopted in this work to evaluate the distribution of residual stresses in aeroengine blades. First, the velocity of Rayleigh surface wave in aeroengine blade was measured by the V(z) curve technique, which can be used to calculate the local residual stress because the change of velocity is thought to be correlated with the contribution from residual stress. Two kinds of plastic-deformed Ti-6Al-4V samples were fabricated by ball-gun shooting to artificially induce distribution of residual stress and then measured by the proposed method. The results indicate that the distribution of the residual stress in both of the samples displays a predictable symmetry. The error of the measured stress is much less than 10% of the yielding stress in Ti-6Al-4V (i.e., about 800 MPa). Finally, the measured residual stresses were verified by X-ray diffraction method, whose results correlate reasonably well with each other. The proposed V(z) curve method and its experimental set-up appear to be a potential in characterizing residual stress at a point-like region, such as in complicated components.
    Type of Medium: Online Resource
    ISSN: 2075-4701
    URL: Article
    DOI: 10.3390/met8080651
    Language: English
    Publisher: MDPI AG
    Publication Date: 2018
    detail.hit.zdb_id: 2662252-X
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  • 9
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    A Novel Baseline-Free Method for Damage Localization Using Guided Waves Based on Hyperbola Imaging Algorithm
    MDPI AG ; 2023
    In:  Sensors Vol. 23, No. 4 ( 2023-02-11), p. 2050-
    Details
    In: Sensors, MDPI AG, Vol. 23, No. 4 ( 2023-02-11), p. 2050-
    Abstract: Most imaging methods based on ultrasonic Lamb waves in structural health monitoring requires reference signals, recorded in the intact state. This paper focuses on a novel baseline-free method for damage localization using Lamb waves based on a hyperbolic algorithm. This method employs a special array with a relatively small number of transducers and only one branch of the hyperbola. The novel symmetrical array was arranged on plate structures to eliminate the direct waves. The time difference between the received signals at symmetrical sensors was obtained from the damage-scattered waves. The sequence of time difference for constructing the hyperbolic trajectory was calculated by the cross-correlation method. Numerical simulation and experimental measurements were implemented on an aluminum plate with a through-thickness hole in the current state. The imaging results show that both the damages outside and inside the diamond-shaped arrays can be localized, and the positioning error reaches the maximum for the diamond-shaped array with the minimum size. The results indicate that the position of the through-hole in the aluminum plate can be identified and localized by the proposed baseline-free method.
    Type of Medium: Online Resource
    ISSN: 1424-8220
    URL: Article
    DOI: 10.3390/s23042050
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
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  • 10
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    Evaluation of Plastic Deformation Considering the Phase-Mismatching Phenomenon of Nonlinear Lamb Wave Mixing
    MDPI AG ; 2023
    In:  Materials Vol. 16, No. 5 ( 2023-03-01), p. 2039-
    Details
    In: Materials, MDPI AG, Vol. 16, No. 5 ( 2023-03-01), p. 2039-
    Abstract: Nonlinear guided elastic waves have attracted extensive attention owing to their high sensitivity to microstructural changes. However, based on the widely used second harmonics, third harmonics and static components, it is still difficult to locate the micro-defects. Perhaps the nonlinear mixing of guided waves can solve these problems since their modes, frequencies and propagation direction can be flexibly selected. Note that the phenomena of phase mismatching usually occur due to the lack of precise acoustic properties for the measured samples, and they may affect the energy transmission from the fundamental waves to second-order harmonics as well as reduce the sensitivity to micro-damage. Therefore, these phenomena are systematically investigated to more accurately assessing the microstructural changes. It is theoretically, numerically, and experimentally found that the cumulative effect of difference- or sum-frequency components will be broken by the phase mismatching, accompanied by the appearance of the beat effect. Meanwhile, their spatial periodicity is inversely proportional to the wavenumber difference between fundamental waves and difference- or sum-frequency components. The sensitivity to micro-damage is compared between two typical mode triplets that approximately and exactly meet the resonance conditions, and the better one is utilized for assessing the accumulated plastic deformations in the thin plates.
    Type of Medium: Online Resource
    ISSN: 1996-1944
    URL: Article
    DOI: 10.3390/ma16052039
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2487261-1
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