9 June 2000 Nonlinear acoustic nondestructive testing for concrete durability
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Several nondestructive testing methods can be used to determine the damage in a concrete structure. Linear ultrasonic techniques, e.g. pulse-velocity and amplitude attenuation, are very common in nondestructive evaluation. Velocity of propagation is not very sensitive to the degrees of damage unless a great deal of micro-damage having evolving into localized macro-damage. This transition typically takes place around 80% of the ultimate compressive strength. Amplitude attenuation is potentially more sensitive than pulse-velocity. However, this method depends strongly on the coupling conditions between transducers and concrete, hence unreliable. A baseline test of the linear acoustics of several mortar samples was conducted. These mortar samples have been previously damaged to different levels. Several other testing methods were also performed on the same samples to form a comparison. The focus is in comparing the sensitivity of a new testing method (Non-linear Acoustic NDE) with several more traditional testing methods. Non-linearity of the material stiffness is expressed in non-linear acoustics as the effect that damage and flaws have on the modulation of a signal as it propagates through the material. Spectral (non-linear) analysis is much more sensitive to lower damage states and less dependent on the repeatability of the coupling of the transducers.
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Hwai-Chung Wu, Hwai-Chung Wu, Kraig Warnemuende, Kraig Warnemuende, } "Nonlinear acoustic nondestructive testing for concrete durability", Proc. SPIE 3995, Nondestructive Evaluation of Highways, Utilities, and Pipelines IV, (9 June 2000); doi: 10.1117/12.387843; https://doi.org/10.1117/12.387843

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