Optimization And Application Research Of High-temperature Digital Image Correlation Method

With the development of China's manufacturing industry,demand for intellectualized and digitalized manufacturing is getting increasingly higher.As an important part of intelligent and digital manufacturing,deformation measurement is very important for China's manufacturing upgrading.The manufacturing updating will benefit a lot from the development of digital image correlation method(DIC)which is one of the most widely used methods for high temperature deformation measurement.In this work,an optimized algorithm for DIC method is proposed based on the classical Newton-Raphson iterative algorithm as well as a prefabricated strain-slicestyle speckling technique for high-temperature.Besides,an experimental system for deformation measurement using high-temperature DIC method is established.With the use of this experimental system,the deformation field caused by thermal expansion of DP600 specimen is obtained as well as its coefficient of thermal expansion(CTE)value with a high accuracy under air-oxidation condition at the temperature up to 1000?.Optimization of algorithm consists of three aspects,imcluding a novel way of delivering the initial value based on the correlation coefficient,a preinterpolation method to rebuild the sub-pixel grayscale field,and eliminating the rigid body rotation and translation.A series of tests based on the computer simulated speckle pattern were conducted to evaluate the accuracy of this optimized algorithm for deformation measurement.Results show that the optimized algorithm has a higher accuracy to measure displacement(less than 8.95E-05 pixel)as well as 300 times calculation speed than the classical Newton-Raphson iterative algorithm.Besides,an easy-to-implement yet effective speckling technique for high-temperature DIC method under air-oxidation condition,called a prefabricated strain-slice-style speckling technique,is proposed in this work.In this prefabricated speckling approach,specimen's preparation and speckling process are completely separated.And spot welding is the only work we need do for speckle preparation.Obviously,the strain-slice-style speckling approach becomes more convenient,less time-consuming and easier to implement compared with common speckling methods such as spray painting and printing.Quantitative quality assessment tests of this prefabricated strain-slice-style speckle were performed,confirming a little better quality than 8 other speckles which were already successfully used in high-temperature DIC method.Also,a heating experiment was comducted to investigate the performance of this prefabricated strain-slice-style speckle.And the results proved that this prefabricated strain-slice-style speckle described in this paper was able to withstand the air-oxidation condition at temperature up to 800? at least for 9 hours without any obvious reduction of speckle's quality for DIC analysis.With the combination use of the optimized DIC algorithm and the prefabricated strain-slice-style speckling approach,an experimental system for deformation measurement using high-temperature DIC method under air-oxidation condition was established successfully.To verify the ability of this experimental system,a thermal expansion experiment was performed,after which the deformation field and the CTE values of DP600 specimen was successfully measured.And a good agreement was met between the reference data and the CTE determined by DIC method of DP600 material,confirming a good effectiveness of this experimental system.Hope that the engineering application of high-temperature DIC measurement method will be expanded to better help the upgrading of China's manufacturing industry.