• A laser-quick and non-destructive method

    From ScienceDaily@1:317/3 to All on Thu Feb 24 21:30:42 2022
    A laser-quick and non-destructive method to detect cracks in concrete structures
    Scientists analyze vibration patterns resulting from laser-induced shock
    waves to detect defects in concrete structures

    Date:
    February 24, 2022
    Source:
    Shibaura Institute of Technology
    Summary:
    Large concrete structures need to be regularly tested for defects
    that may compromise their stability. While acoustic tests performed
    by certified inspectors are usually the inspection method of
    choice, these tests take longer to perform as the structure's size
    increases. In a new study, scientists developed a new method to
    identify defects using shock waves generated by laser-induced
    plasma. The new method is faster, completely non-destructive,
    and allows for timely evaluation of concrete infrastructure.



    FULL STORY ========================================================================== Nothing is truly set in concrete, and this is especially true for
    structures made of concrete. When structures made of concrete like
    bridges, buildings, and tunnels are loaded repeatedly over long
    periods, they develop cracks that may progress and cause structural
    failure. Regular inspections are therefore needed to detect cracks before
    they become a cause for concern.


    ========================================================================== Conventionally, defects in concrete structures are detected using the
    acoustic test called the "hammering method" performed by certified
    building inspectors.

    However, these tests take time to complete and as with most skill-based techniques, the effectiveness of the test is dependent on the expertise of
    the inspector. Moreover, as the number of aging infrastructures continues
    to rise, a method of inspection that is fast and reliable is paramount
    for ensuring the safe operation and long-term use of the structure.

    An alternative inspection method for testing involves generating shock
    waves near the surface of the concrete structure. The shock waves
    induce vibrations on the structure which can be analyzed to detect
    defects. However, in such tests, it is necessary to generate shock waves
    that do not damage the structure. In this regard, laser-induced plasma
    (LIP) shock wave excitation has shown great promise. The technique has
    been used to detect defects in a variety of structures, ranging from
    pipes to fruit surfaces. In this method, the shock waves are generated
    by colliding laser-generated plasma with air.

    In a new study, researchers from Shibaura Institute of Technology and
    the National Institutes for Quantum Science and Technology, Japan,
    tested the effectiveness of this method at detecting cracks in concrete structures. "We used LIP shock waves as a non-contact, non-destructive
    impulse excitation. This allows for remote and completely non-destructive detection of defects in concrete structures," explains Naoki Hosoya,
    a Professor at the Department of Engineering Science and Mechanics at
    Shibaura Institute of Technology and the corresponding author of the
    study. Their findings have been published in the International Journal
    of Mechanical Sciences.

    To evaluate the new method, the researchers exposed a concrete block
    that had an artificially created defect to a shock wave generated by a high-power pulsed laser. The vibrations were then analyzed at multiple
    points on the concrete surface inside and outside the defect area. The
    analysis revealed the presence of Rayleigh waves at the site of the
    defect. These are surface waves that move at a faster velocity than
    other shock waves. The researchers were able to successfully determine
    the defect areas by detecting the points where these Rayleigh waves
    were reflected. "Defects in the concrete specimen can be detected and
    the location of the approximate boundary can be determined using the propagation of Rayleigh waves," explains Prof. Hosoya.

    By visualizing Rayleigh waves, defects in a structure can be detected
    much faster than with other telemetric methods which analyze vibrations,
    making it a useful method for non- destructive testing of concrete
    structures. "The advantage of using Rayleigh waves to detect defects
    is that fewer measurement points are necessary compared to measuring
    the natural mode. Additionally, the time required for defect detection
    can be shortened. Visualizing Rayleigh waves propagation has potential
    for practical detection of the configurations and defects in concrete," elaborates Prof. Hosoya.

    In conclusion, the use of LIP shock waves to assess cracks in concrete structures is a safe and rapid method that can be used to maintain infrastructure and prevent structural failure.

    ========================================================================== Story Source: Materials provided by
    Shibaura_Institute_of_Technology. Note: Content may be edited for style
    and length.


    ========================================================================== Journal Reference:
    1. Sho Wakata, Naoki Hosoya, Noboru Hasegawa, Masaharu
    Nishikino. Defect
    detection of concrete in infrastructure based on Rayleigh
    wave propagation generated by laser-induced plasma shock
    waves. International Journal of Mechanical Sciences, 2022; 218:
    107039 DOI: 10.1016/ j.ijmecsci.2021.107039 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/02/220224140837.htm

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