Application of improved surface fitting algorithm in digital image correlation method on concrete blasting process

To further investigate the failure process of concrete in demolition blasting, the concrete blasting experiments were conducted. The digital image correlation (DIC) method was used to measure the full field surface deformation. In the DIC method, the surface fitting sub-pixel displacement algorithm has simple structure and high computational efficiency, however, the accuracy is poor. A new surface fitting algorithm based on moving least square method with a Gaussian basis function and a 3×3 fitting window was used and the accuracy was improved to 1/200 pixel. The blasting experiment results show that the failure of concrete is driven by blasting stress wave and gas. The action time is about 4.5 ms. The formation of crack is dominated by stress wave. The maximum velocity of crack propagation is 225.95 m/s, the average velocity is 122.27 m/s, and the time is about 1.75 ms. The gas mainly makes the crack to expand, and then divides the concrete. Under explosion loading, the concrete also shows a fracture process zone, and a strain concentration is formed at the crack tip. The length of the fracture process zone is 8~9 times of the maximum aggregate size.