Digital image correlation based on the pre-deformation assist strategy and an optimized checkerboard-like speckle pattern for large deformation measurement.

Large deformation measurement is one of the main issues faced by the digital image correlation method, and the specially designed speckle pattern offers a promising solution. This Letter suggests an extremely simple method to fabricate an optimized speckle pattern for large deformation problems. It demonstrates a more effective large deformation initial estimation capability and measurement accuracy when combined with the pre-deformation assist strategy. A series of simulated and real experiments are used to test the effectiveness of the proposed method, and the results reveal that it performs significantly better than the traditional method in large deformation problems.

Digital volume correlation using a spherical shell template and cubic element for large rotation measurement.

The displacement hypothesis of eight-node cubic elements is selected as the shape function of digital volume correlation (DVC), and the Newton-Raphson iterative method is selected to solve the partial differential equation to measure the displacement field. In order to ensure that the DVC algorithm is usable under the large rotation condition, the spherical shell template matching technique is presented to perform the integer-voxel displacement searching for nodes, which can provide the optimal initial values for the Newton-Raphson iterative method due to the rotation and translation invariance of the spherical shell template. Simulated volume images are used to verify the reliability of the proposed method, and the results show that the proposed DVC method can be used to measure the deformation with an arbitrary rigid body rotation angle. This work is expected to be useful to measure deformation with large rotation of the internal structure of materials.