| 摘要 |
PURPOSE:To precisely check inner cracks of a concrete product by surveillance with the criterion of a sound pressure peak width value in a sound pressure waveform of the sound collecting total frequency region of a noise meter microphone. CONSTITUTION:To make impact force constant, a concrete product (e.g. ALC product) 1 is impacted vertically in the impact plane by using a hammer device 3 with a hammer head 2 fitted to the tip of an air cylinder. Its impact sound is collected by a noise meter 4 set up near the device 3, and a peak value of the ac voltage signal corresponding to the magnitude of a sound pressure outputted from the noise meter 4 and recorded by a high-speed Fourier transformer 5. That is, a large difference appears between the sound pressure of a crack part and that of a non-defective part, depending upon the way to develop an impact sound, and the ratio of the sound pressure of a crack part to that of a non-defective part is twice or more; therefore, a defect criterion value is set to survey whether or nor this criterion value is exceeded, thereby easily checking inner defects. |
