GRAIN-SIZE MEASUREMENT

摘要

Grain sizes, for example in a sheet (12), are monitored by generating broadband ultrasonic waves with a pulse laser generator (14) at a first location (18) on a surface of the object, and observing with a laser detectro (20, 36) the waves on the surface at a different location (A). The ultrasonic spectrum for those waves that arrive at arrival times after that of the Rayleigh waves or the start of the A0 Lamb waves is determined, and the high frequency power is compared to the low frequency power. This ratio gives a consistent relationship to grain sizes. With copper sheets the frequency windows may be 1 to 3 MHz as the low frequency region, and 2.2 to 15 MHz as the high frequency region.