Method of and apparatus for measuring elongation of a test specimen

Abstract

Method and apparatus for measuring elongation in a contactless manner capable of obtaining accurate measured value without attaching reference lines and capable of being automated, wherein laser beams are irradiated from two sensor sections each comprising a laser projector and a CCD camera to prescribed reference line positions at two positions on a test specimen, laser reflection lights are photographed respectively as speckle patterns each comprising a plurality of fringes respectively by the CCD cameras, the fringes at predetermined positions the speckle patterns are recognized on the coordinate of the CCD camera screens as targets correspondingly to the prescribed reference line positions at two positions respectively, and the moving amount on the pixel unit basis on the coordinate of the target fringes that move in accordance with the elongation of the test specimen are detected respectively to determine the elongation information of the test specimen, the fringes of the speckle patterns photographed by the CCD cameras may be image converted into the marks at the predetermined positions of the television camera screens. Stopping or disturbance of image of the speckle patterns of the CCD camera appearing just before the fracture of the test specimen may be sensed to stop the application of the tensile load on the test specimen.

Description

[0001] 1. Field of the Invention[0002] This invention concerns a method of and an apparatus for measuring elongation of a test specimen in a contactless manner without attaching reference lines (or reference points) to a test specimen and, more in particular, it relates to a method of and an apparatus for measuring elongation by utilizing the amount of movement of fringes in speckle patterns that appear in the reflection light of laser beams irradiated to the test specimen.[0003] 2. Related Art Statement[0004] As the means for measuring the elongation of a test specimen in a contactless manner, there has been a method of attaching reference lines at two points in the direction of elongation of the test specimen, photographing respective reference lines by two television cameras individually which are recognized by a computer as marks for each of them on a television screens, calculating the moving amount of the marks on the television screens that move along with the elongation of t...

AI Technical Summary

Problems solved by technology

However, the former method, that is, a method of using the television cameras involves a fetal drawback that reference lines have to be attached to the test specimen.

However, the measuring method of appending the reference lines involves problems such as of giving undesired effects on the strength of the test specimen, peeling of the seal, elongation of the reference lines per se making the reference base obscure and, further, causing chemical change to the test specimen by the ink of the reference, which hinders accuracy and efficiency of the test.

That is, since the speckle pattern recognized by the image sensor is converted and used as electric signals, it is difficult to attain high measuring accuracy unless precise optical parts and conversion devices are used.

Therefore, if the test specimen and the laser beam are laterally displaced relative to each other during measurement, the speckle pattern per se as a reference base becomes inaccurate to bring about a problem that there is no reliability at all for the measured value.

Particularly, since the tensile load is applied on the test specimen during measurement and slight lateral deviation is inevitable, this problem is fetal for the measurement.

Further, as a general problem in the existent measurement for elongation, since elongation at break is determined based on the distance between the reference lines before applying the tensile load and the final distance between the reference lines upon rupture of the test specimen by the tensile load, tensile load is applied till rupture occurs in the test specimen.

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