• Smart Structures and Systems
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• v.17 no.1
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• pp.73-89
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• 2016

The stress dependence of ultrasonic wave velocity is known as the acoustoelastic effect. This effect is useful for stress monitoring if the acoustoelastic coefficient of a subject medium is known. The acoustoelastic coefficients of metallic materials such as steel have been studied widely. However, the acoustoelastic coefficient of concrete has not been well understood yet. Basic constituents of concrete are water, cement, and aggregates. The mix proportion of those constituents greatly affects many mechanical and physical properties of concrete and so does the acoustoelastic coefficient of concrete. In this study, influence of the water-cement ratio (w/c ratio) and the fine-coarse aggregates ratio (fa/ta ratio) on the acoustoelastic coefficient of concrete was investigated. The w/c and the fa/ta ratios are important parameters in mix design and affect wave behaviors in concrete. Load-controlled uni-axial compression tests were performed on concrete specimens. Ultrasonic wave measurements were also performed during the compression tests. The stretching coda wave interferometry method was used to obtain the relative velocity change of ultrasonic waves with respect to the stress level of the specimens. From the experimental results, it was found that the w/c ratio greatly affects the acoustoelastic coefficient while the fa/ta ratio does not. The acoustoelastic coefficient increased from $0.003073MPa^{-1}$ to $0.005553MPa^{-1}$ when the w/c ratio was increased from 0.4 to 0.5. On the other hand, the acoustoelastic coefficient changed in small from $0.003606MPa^{-1}$ to $0.003801MPa^{-1}$ when the fa/ta ratio was increased from 0.3 to 0.5. Finally, it was also found that the relative velocity change has a linear relationship with the stress level of concrete.

• Structural Engineering and Mechanics
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• v.91 no.4
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• pp.357-368
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• 2024

In this study, a finite-element surface wave simulation using an effective elastic constant (EEC) was developed to calculate the Rayleigh wave velocity change and polarization change in aluminum, steel, and concrete under uniaxial stress. Under stress, an isotropic medium behaves like an anisotropic material during the wave propagation. The EEC is an equivalent anisotropic stiffness matrix which was derived to simulate the acoustoelastic effect using classical finite-element software. The vertical and horizontal surface displacements located 8-mm from a 1-㎲ excitation load were used to find the acoustoelastic coefficients k^v and k^p and compared to an analytical scheme. It was found that k^v for aluminum and concrete matched within 4% of the analytical solution. The finite-element simulation showed that the Rayleigh wave arrival time for concrete and aluminum was greatly influenced by the stress level. Thus, predicting the stress level using concrete and aluminum's acoustoelastic effect is applicable.