1 September 2015 Digital speckle-based stereo microscope strain measurement system for sheet metal forming by hydraulic bulge tests
Author Affiliations +
A digital speckle based stereo microscope strain measurement system is developed to investigate the forming limit diagram (FLD) of miniature sheet metal under hydraulic bulge testing conditions. A stochastic speckle pattern is sprayed on the surface of the tested metal before forming. A series of images are recorded by two cameras mounted on a binocular stereo microscope during the hydroforming process. The critical major and minor strains are then calculated and plotted to construct the forming limit curve. The key technologies applied in the system are discussed in detail, including stereo microscope calibration and large deformation strain filed determination. First, considering complex optical paths and high magnification of the stereo microscope, an accurate combined distortion correction model is proposed to optimize the intrinsic and extrinsic parameters of the stereo microscope. Then, to solve the problem of strain measurement of the tested metal in large deformation situation, a large deformation measurement scheme based on deformation continuity of adjacent images is proposed. And an algorithm of limit strain determination based on spline model is proposed to calculate the critical strains at the onset of plastic instability. Finally, with our self-developed stereo microscope imaging system and sheet metal hydraulic bulging setup, FLD determination tests are conducted to validate the performance of the system. And the measured FLD is compared with the simulation results that predicted by the finite element method. The simulation and experimental results confirm that the proposed system is feasible to measure the full-field strain during the whole bulging processes and provides a better solution for forming limit diagram prediction.
© (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Maodong Ren, Maodong Ren, Jin Liang, Jin Liang, Lizhong Wang, Lizhong Wang, Bin Wei, Bin Wei, } "Digital speckle-based stereo microscope strain measurement system for sheet metal forming by hydraulic bulge tests", Proc. SPIE 9576, Applied Advanced Optical Metrology Solutions, 95760D (1 September 2015); doi: 10.1117/12.2187350; https://doi.org/10.1117/12.2187350

Back to Top