A piezoelectric polyvinylidene fluoride film stress sensor was developed to measure the contact pressure on the sheet near the cutting edge in the fine-blanking process. Two cases with and without cracks in the fine-blanking surface were studied. The relationship between the contact pressure and crack width was investigated using the Kriging methodology at different punching speeds. The maximum contact pressure appeared at the beginning of sheet punching, but not at the end of V-ring indention. For the case with and without cracks in the fine-blanking surface, one and two fluctuations of contact pressure are observed, respectively. Using the Kriging model, a fine-blanked surface with a reduced crack width can be obtained using the optimal values of contact pressure and punching speed.

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In this paper, a measurement system based on stereo photogrammetry is proposed for position and attitude measurements of test models in hypersonic wind tunnel testing. Several adaptations were made to an existing stereo photogrammetry system to promote its routine use as a primary wind tunnel measurement system. First, cameras were installed in the wind tunnel test section to decrease the measurement distance and increase the base length, which helped improve the measurement accuracy. To deal with camera vibration caused by the freestream, a camera orientation method is proposed to estimate the exterior parameters of each frame relative to the tunnel coordinate system. Second, a scheme to determine the model coordinate system is proposed, which does not require placement of the targets at known locations of the model. Third, to solve the recognition problem of motion-blurred target images, a network was adopted for stereo deblurring and a stereo blur dataset simulating the wind tunnel test environment was generated for network training. To develop the novel stereo photogrammetry system, experiments were conducted in both the laboratory and a hypersonic wind tunnel at the China Aerodynamics Research and Development Center. The experimental results suggest that the proposed measurement system is practicable for position and attitude measurements of test models in hypersonic wind tunnel testing.

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