Full-field Measurement Method For High Temperature Deformation Of Materials

The deformation measurement of materials at high temperatures is very important in the aerospace and manufacturing fields.It is a key measure to test the mechanical properties and endurance of materials in high temperature environments.Using digital image correlation method to measure the deformation of specimens has become one of the mainstreams of testing mechanical properties.However,using this method in high temperature environments has many interferences.For example,the weak correlation interference of high temperature radiation,strong light interference,etc.make the quality of the collected images very poor.And high temperature is often accompanied by large deformation of the specimen,The large deformation makes the stereo matching of the image inaccurate,and the corresponding point cannot be found during the matching.In order to solve the above problems,this paper proposes a solution that can stably calculate the deformation of sheet metal specimens in a high-temperature environment.The main contents are as follows:(1)Aiming at the strain measurement on the surface of a large-deformed sheet material,this paper adopts an algorithm based on diffusion seed points and step-by-step matching.The seed point algorithm is to select one or several seed points in the measured area,and then calculate the adjacent pixel position of the seed point pixel after accurately matching the seed point.Then,the calculated neighbor pixels are used as new seed points for diffusion calculation.The step-by-step matching algorithm is different from the traditional stereo matching,that is,all states use the first frame as a reference,and the step-by-step algorithm uses the previous frame or the previous frames as the reference image for matching.The above two methods can effectively solve the problem that the corresponding point cannot be tracked when the deformation is too large.(2)Aiming at the problem of high-temperature environment heat radiation and strong light interference when collecting images,this article adds air circulation equipment and filters to the hardware.Image processing methods such as DOG pyramid,Gaussian low-pass filtering and morphological correction are also used to solve the problem of high temperature weak correlation and strong light.The DOG pyramid method improves the texture of the image.Gaussian low-pass filtering can effectively reduce strong light interference by filtering strong light noise;Finally,the morphological correction can further reduce the interference of strong light.After the above-mentioned processing,the image will eventually become dark,and finally the brightness and contrast of the image are improved through normalization.(3)Finally,in order to verify the accuracy of the above method,three groups of controlled experiments were carried out.They are high-temperature tensile test,high-temperature laser experiment and high-temperature welding experiment.The three sets of experiments are compared with high-precision strain gauges and extensometers.The accuracy is about 2%,which meets the standard.The method proposed in this paper that can effectively measure deformation at high temperature can solve most of the problems caused by high temperature,such as weak correlation of high temperature radiation,weak correlation of large deformation and strong light interference.Compared with the contact measurement method,this method has the advantages of simple operation and less influence of temperature.Through the multi-group accuracy control test of this scheme,it can be concluded that this scheme has high accuracy and stability.