High-precision optical extensometer based on telecentric lens and measuring method

Abstract

The invention discloses a high-precision optical extensometer based on a telecentric lens and a measuring method. The high-precision optical extensometer comprises a digital camera, an object side telecentric or bi-telecentric lens, four reflectors, a camera support and a data processing device. The measuring method is characterized in that: the digital camera and the telecentric lens are used totrack a target point, and false displacement and false strain caused by an out-of-plane displacement of a sample surface and a single-camera pinhole imaging model can be eliminated by virtue of the imaging characteristic of the telecentric lens that the telecentric lens is insensitive to depth, thus an in-plane displacement and strain measuring precision of a sample are greatly improved.

Description

technical field [0001] The invention relates to a high-precision optical extensometer and a measurement method based on a telecentric lens, belonging to the fields of optical measurement and nondestructive testing. Background technique [0002] Strain measurement has always been one of the important goals in the fields of structural failure analysis, material performance testing, and industrial deformation monitoring. Traditional strain measurement technologies mainly include contact and non-contact measurement technologies. [0003] Contact measurement techniques such as resistance strain gauges, fiber optic strain gauges, or mechanical extensometers often add additional mass to the sample to be tested, and may also strengthen the sample to a certain extent due to the use of adhesives, making these Measurement methods are increasingly unsuitable for the detection of samples such as biological materials and thin film materials. [0004] In the non-contact measurement techno...

AI Technical Summary

Problems solved by technology

[0004] In the non-contact measurement technology, the two-dimensional and three-dimensional digital image correlation technology used for full-field measurement still needs to improve the detection accuracy of strain. At present, more and more video extensometers based on optical methods have appeared. For example, Instron company has Commercialized video extensometers, strain measurement accuracy can not meet the needs of practical applications

More importantly, under actual experimental conditions, the sample will have a certain out-of-plane displacement due to various reasons. Under the traditional pinhole imaging model, the out-of-plane displacement will produce false displacement and false strain on the image plane of the imaging system. Can significantly interfere with the accuracy and resolution of strain measurements

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