| 摘要 |
PROBLEM TO BE SOLVED: To ensure high accuracy nondestructive measurement regardless of presence of a filler or an iron rod by sampling an oscillating elastic wave astride a crack and measuring the depth of a crack, based on the amplitude of a signal in front and rear of the crack. SOLUTION: Surface of a structure is oscillated by hitting it with a hammer, or the like, and an oscillation signal is sampled by means of a plurality of acceleration pickup sensors positioned on the opposite sides of a crack. In this regard, a surface wave is employed along with energy (speed or displacement amplitude) as a physical quantity. The wave energy decreases during propagation process and attenuates slightly due to viscosity of the structural material. The wave energy is varied across a crack and the extent of variation increases as the depth of the crack increases. Based on the propagation characteristics, acceleration signal in the data sampled by each sensor is integrated and converted into a speed signal thus correcting the effect of geometric attenuation in the amplitude of surface wave speed, wall thickness or sharing wave component. Depth of a crack is calculated using a corrected amplitude ratio determined through corrective analysis and a surface wavelength. |
