Elongation measuring method and laser noncontact extensometer

Abstract

The present invention is arranged such that: laser light is irradiated onto the surface of a specimen over a predetermined length thereof in the direction of elongation to be measured; that scattering light of the laser light reflected from the specimen surface is photoelectrically converted to obtain speckle pattern data; out of the speckle pattern data thus obtained, the data from two zones on the specimen which are separated from each other by a predetermined distance in the elongation direction, are initially set as observation point data; with the use of the observation point data, the amounts of movement of the speckle patterns from the two zones on the specimen are calculated; the zones serving as observation point data sources are shifted in the speckle pattern movement direction each time the calculation results of the speckle pattern movement amounts reach a predetermined amount; and the elongation of the specimen between the initially set two zones is calculated based on (i) the shift amounts of the observation point data sources and (ii) the speckle pattern movement amounts calculated with the use of the observation point data.