Research On Binocular Vision-based Materials Stress-strain Measurement Technique

Plasticity and tenacity are two important parameters which reflect the mechanical properties of the materials. The stress-strain curves explain the law of plasticity during tensile process, which is an important basis for evaluating the mechanical properties of materials. With the developed requirement of the modern science and technology to the mechanics test of materials, the extensometer is unable to meet the current requirement. Therefore, a non-contact stress-strain curves measurement method, which is based on binocular stereo vision, is proposed in this thesis. The main research contents and innovative points are summarized as follow:1. The method of the force data collection in the tension test is been studied, and the material force data collection system which is based on the computer, SCM and computer bus interface has been built. The real-time and efficient force data acquisition in the tension test is taken into practice.2. On the basis of deep research on the binocular stereo vision theory, the author build the image acquisition system for the deformation during the material's tensile process, and design the hardware circuit for the force and image acquisition.. The precise synchronization of the stress and strain in the sequence is realized.3. A node extraction algorithm based on the image of simple grid is proposed, and the node matching based on the simple grid topology is realized. The problem of the stress-strain curve' measurement for the titanium foil(TC1) has been solved.4. In view of the dense grid image in the coordinate grid method, an adaptive grid node localization algorithm based on region growing method is proposed. And realize the stable and efficient grid nodes extraction. Aims at the problem of matching the repetitive structure's points which have the same name in dense grid images, the stereo matching algorithm based on epipolar geometry and the sequential matching algorithm based on artificial mark dots is proposed, which realized the node matching based on dense mesh topology.The experiment is carried out based on the research of the key technologies. Based on the algorithm of simple grid, the problems in the measurement of the stress-strain curve of titanium foil(TC1) are solved effectively, And the measurement of aluminum alloy's stress-strain curve is realized based on the dense grid. The experimental results show that the proposed technique is practical and effective.