In-situ measurement of metal thermal strain based on laser speckle DIC technology
The digital image correlation method of laser speckle can be used to realize the non-contact and in-situ measurement of metal micro-strain,but the image quality of laser speckle,such as uniformity,gray gradient,stability and so on,has a great influence on the strain measurement accuracy.In order to improve the accuracy and precision of the DIC method of laser speckle for the measurement of metal strain,the laser selection,laser wavelength,beam expansion system and imaging system are designed,improved and tested in detail in this paper.Through the quantitative analysis of the image quality evaluation parameters such as speckle size and duty cycle before and after the improvement of the optical system,the factors affecting the strain measurement accuracy of laser speckle DIC method are determined.And by optimizing the parameters of the optical path such as laser power,exposure time,junction length,and image distance,the speckle images with more uniform distribution and better quality in full field were obtained,which improved the accuracy and precision of strain measurement by the laser speckle DIC method.Finally,the DIC method of laser speckle is used to measure the thermal strain of metal aluminum heated from room temperature to 360℃ in non-vacuum environment.The measured results are in good agreement with the theoretical values,and the relative error decreases with the increase of temperature,which proves the feasibility of this method in metal thermal strain measurement.
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