A Dual Field of View Video Extensometer Based on Telecentric Lens and Cube Prism

Abstract

The invention discloses a dual-field video extensometer based on a telecentric lens and a cubic prism. The telecentric lens can be used for high-precision displacement tracking, which can not only eliminate the adverse effects caused by lens distortion, but also avoid the adverse effects of camera self-heating and off-plane displacement on the measurement results; by using the refraction principleof the cubic prism, the telecentric lens can perform synchronous and high-spatial resolution capture on two discontinuous fields of view on the surface of a test piece to be tested; the displacementswith a sub-pixel accuracy of two discrete test points can be accurately tracked and calibrated by using an image registration algorithm of a digital image correlation method; the gauge distance is estimated through the cubic prism; and the average strain between the two test points and the Poisson ratio of the test piece can be determined by processing the experimental data later. The telecentriclens only captures images of two fields of view containing two test points and the surrounding areas, rather than the entire image of the test piece to be tested; therefore, a large gauge distance, high-accuracy, and ultra-sensitive average strain measurement can be realized.

Description

technical field [0001] The invention relates to the technical field of optometry, in particular to a dual-field video extensometer based on a telecentric lens and a cubic prism. Background technique [0002] Using mechanical testing methods to characterize the mechanical properties of materials is an essential way to design and analyze material structures, and it has always been the focus of researchers and engineers. Among the many advanced mechanical testing methods, uniaxial tension and compression testing using a universal testing machine (UTM) is the most effective and widely adopted method because of its simplicity, directness, and has been successfully used to characterize materials Important parameters such as elastic modulus, Poisson's ratio, and ultimate tensile strength. In order to estimate these material properties, an efficient means of accurately measuring the strain on the surface of the test piece is required. The methods used to measure the surface strain...

AI Technical Summary

Problems solved by technology

Non-contact measurement method In the real experiment, due to the existence of factors such as imperfect loading, camera self-heating, and material Poisson's ratio, out-of-plane displacement will occur, and a small out-of-plane displacement will produce a large virtual strain. Moreover, the magnification Changes in the measurement results will also produce a huge virtual strain, which will reduce the accuracy of the measurement results

In addition, for a video extensometer composed of a single camera and a conventional lens (which satisfies the ideal pinhole model), due to the unavoidable out-of-plane displacement of the tested piece during the stretching process, the out-of-plane displacement will change the imaging relationship of the imaging system, thus Therefore, this single-camera video extensometer using an ordinary camera has the problems of large measurement error and low precision; if the three-dimensional digital image correlation method (3D-DIC) based on binocular stereo vision is used ) is used as a video extensometer, although it can simultaneously measure the displacement of the test piece in all directions and does not need to consider the influence of out-of-plane displacement, but the system and algorithm are very complicated, and the binocular stereo vision system needs to be calibrated in advance

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