Browsing by Subject "Ultrasonic"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Advancements in Imaging of Concrete Members Using Shear Waves
    (2018-12) Asadollahi, Aziz
    The emergence of linear array devices employing dry point contact transducers emitting horizontal shear waves significantly increased the efficiency of data acquisition and enabled using imaging techniques for nondestructive evaluation of concrete members. Reverse time migration (RTM) is a mechanics-based imaging technique that has gained the attention of researchers in the context of nondestructive testing (NDT) in recent years. RTM offers a better focusing over synthetic aperture focusing technique (SAFT), a well-established real-time imaging method for NDT of concrete members, and enables locating reflectors with steep slopes and the bottom boundaries of embedded objects. Despite all advantages, RTM suffers from some limitations. It is computationally costly and demands a massive memory. In addition, RTM algorithm generates images with high-amplitude artifacts and assigns amplitudes to the points of a reconstructed image that are not a true representative of the reflectivity of the scanned medium at those points. This dissertation develops an analytical approach to resolve the computational cost and memory demand bottlenecks of the RTM when dry point contact transducers emitting horizontal shear waves are used for data acquisition. Horizontal shear waves preserve more energy than longitudinal waves after emission allowing inspection of concrete members in deeper depths. However, the lower wavelength of shear waves increases the potential of scattering by aggregates and air voids that affects the quality of the reconstructed images. This dissertation develops a 3D numerical tool to study the scattering attenuation of shear waves in concrete. An efficient algorithm is introduced to generate non-overlapping aggregates and air voids to study the effect of size, shape, and material properties of aggregates as well as the porosity of concrete on the scattering attenuation of shear waves. Moreover, it develops novel techniques to mitigate the high-amplitude artifacts of RTM images and to adjust the amplitudes assigned to the points of an image reconstructed by RTM for homogeneous and concrete members.
  • Thumbnail Image
    Item
    Nondestructive Evaluation Advancements for Damage Detection in Concrete
    (2016-06) Freeseman, Katelyn
    While concrete is the most widely used civil engineering material, damage detection and progression in concrete structures have still proven to be difficult to address, especially when only one-sided access is available. New technological advances in nondestructive testing technology have created the opportunity to better utilize ultrasonic waves to aid in this damage detection process. However, interpretation of the signal data is a challenging task which often requires subjective assessments. This thesis addresses these limitations via the utilization of ultrasonic array technology for nondestructive damage detection purposes. The ultrasonic shear velocity array system used for this research is particularly advantageous because it can obtain measurements on virtually any concrete specimen, from columns and beams to concrete pavements, and provides a wealth of data from a single measurement. Novel signal interpretation methods were developed for several important concrete applications. Detection of load-induced damage in laboratory beams and a full-scale reinforced concrete column, as well as standard life-cycle damage in concrete pavements caused by freeze thaw or alkali-silica reaction degradation were considered. These investigations culminated in the development of successful and efficient quantitative damage detection methods. Finally, the development and refinement of a simulation program allowed for verification of the experimental investigation and a greater understanding of signal results.