Abstract
Based on the velocities of waves near the surface in concrete, the propagation path and travel time of different waves were calculated, and the influence of crack on these waves was analyzed. Some theoretical conclusions were verified by FEM. The ultrasonic waves were received by array transducers and the velocities of different waves were calculated and distinguished according to wave velocity in the simulation. Simulation results show that when sound wave propagates through the crack, longitudinal waves will arrive at the receiving arrays, and the crack will diffract transverse wave to generate new longitudinal wave and transverse wave by mode conversion, and Rayleigh wave will propagate along the surface (including the crack side wall). Finally, it is found that the relationship between crack depth and amplitude and energy is approximately linearly monotone decreasing by studying the waves near surface with different crack depths.
Highlights
With the development of modern society, many engineering like motorway, bridges and dams demand lots of concrete whose bulk is huge
Simulation results show that longitudinal waves arrived at the receiving array at twice, and the crack diffracted transverse wave to generate new longitudinal wave and transverse wave by mode conversion, and Rayleigh wave propagated along the surface, when sound waves near the surface propagated through the crack
(2) According to (1), the original longitudinal was diffracted by crack tips; the velocity of transverse caused by diffraction is slower, so the transverse wave will converse into longitudinal wave by mode conversion when the wave propagated near the surface
Summary
With the development of modern society, many engineering like motorway, bridges and dams demand lots of concrete whose bulk is huge. There are many methods used in detecting surface opening cracks in concrete, such as: (1) single ultrasonic flat-measured method; (2) perforating method; (3) Rayleigh wave methods. The perforating method breaks workpiece, and much costs ; the single ultrasonic flat-measured method detect cracks less than 500mm; the Rayleigh wave method has these advantages: (1) large energy; (2) not affected by fluid; (3) flexible detection for its propagation character. Ultrasonic method has its advantages in detecting surface opening cracks, it’s necessary to analyze the influence of the surface opening cracks on the waves near surface including Rayleigh wave. Based on the sound velocity of different wave modes near the concrete surface, this paper will analyz the influence of cracks on the waves near surface, and distinguishes the waves near surface by utilizing receiving array. Simulation results show that longitudinal waves arrived at the receiving array at twice, and the crack diffracted transverse wave to generate new longitudinal wave and transverse wave by mode conversion, and Rayleigh wave propagated along the surface (including the crack side wall), when sound waves near the surface propagated through the crack
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