Metrological assessment of multi‐sensor camera technology for spatially‐resolved ultra‐high‐speed imaging of transient high strain‐rate deformation processes

Abstract

The present work proposes a metrological route for capturing spatially‐resolved ultra‐high‐speed kinematic full‐field data from high strain‐rate experiments and multi‐sensor camera technology. This paper focuses, from an application point of view, on highly resolved rotating mirror cameras, such as the Cordin‐580. This camera allows 78 frames of 8 megapixels to be recorded at up to 4 million frames per second (fps). The optical apparatus induces distortions that need to be taken into consideration. Distortions are modelled with Zernike polynomials and recovered using Digital Image Correlation (DIC) with a tailored synthetic speckle pattern. Effective displacements can then be quantitatively obtained with subpixel precision. After an assessment of the calibrated camera performance, this methodology is used to record, at 480,000 fps, the fracture of a pre‐notched sample subjected to an inertial impact test. The kinematic fields obtained quantitatively captured the events occurring during the test, such as the compression wave and the induced Poisson effect, the Mode‐I crack initiation and the shear strain concentration at the notch tip. The achievement of a DIC displacement and strain random error of, respectively, 5 μm (0.15 pixels) and 2 mm m−1, combined with a high spatio‐temporal sampling, provides a promising way for quantitatively analysing very fast transient and heterogeneous phenomena.