Dynamic caustics in conjunction with high-speed photography were used in experiments to investigate the interaction of obliquely incident blast stress waves with running cracks. The dynamic photoelastic experiment method was used to supplement and improve the effects of different blast stress wave properties on the running crack. This indicated that the crack-tip mode II stress field affected the crack deflection direction. When the moving crack-tip mode II stress intensity factor K_II was positive, the crack deflected clockwise. When the stress intensity factor K_II was negative, the crack deflected in the counterclockwise direction. The incident direction of the blast stress wave affected the deflection of the crack. When the direction of the blast stress wave was the same as the direction of the moving crack propagation, the moving crack deflected away from the blast wave source. When the blast stress wave propagation direction was opposite to the crack propagation direction, the crack deflected toward the blast wave source. During the interaction of an obliquely incident blast stress wave with a moving crack, the P wave caused the deflection of the crack. The tails of the P wave and S wave interacted with the kinked crack to increase the mode I stress intensity factor K_I and the crack propagation velocity.

The research on blasting damage of medium has important engineering significance, wherein one of the main factors affecting the blasting effect of the medium is the free boundary of the medium. In this article, the blasting damage of media with one free boundary is studied and the damage evaluation based on fractal theory is carried out. Firstly, an experimental device is designed to simulate the state of the medium’s one free boundary. The distance between blasthole and the free boundary is the only variable considered in the experimental investigation. The fractal theory is used to analyze the fractal damage of the medium caused by the explosion, and MATLAB is used to extract three characteristic parameters (damage depth, damage width, and damage zone) of the binary image after the explosion. Finally, LS-DYNA is used to build a 2D plane strain model with the same size and boundary conditions, which simulates the damage evolution process of medium under a single free boundary blasting pattern. The fractal theory is then used to evaluate the fractal damage observed in the numerical simulation results. The experimental results and numerical simulation results of blasting fractal damage of one free boundary medium are in good agreement. The blasting fractal damage grows initially and subsequently decreases as the distance between the blasthole and the free boundary increases. Thus, the distance between blasthole and free boundary affects the efficiency of blasting energy destroying medium and the blasting failure pattern.

Effects of defects on the dynamic fracture behavior of engineering materials cannot be neglected. Using the experimental system of digital laser dynamic caustics, the effects of defects on the dynamic fracture behavior of nearby running cracks are studied. When running cracks propagate near to defects, the crack path deflects toward the defect; the degree of deflection is greater for larger defect diameters. When the running crack propagates away from the defect, the degree of deflection gradually reduces and the original crack path is restored. The intersection between the caustic spot and the defect is the direct cause of the running crack deflection; the intersection area determines the degree of deflection. In addition, the defect locally inhibits the dynamic stress intensity factor of running cracks when they propagate toward the defect and locally promotes the dynamic stress intensity factor of running cracks when they propagate away from the defect.

The depth of mineral resources like coal continuously increases due to the exhaustion of shallow resources, and the characteristic of high ground stress in deep ground inevitably affects fracture of rock blasting. Combining with high‐speed photography technology, the digital image correlation method (DIC) is introduced into experimental study on explosive mechanics. And strain evolution process of blasting under high stress condition is obtained by using the model experiment method. The preliminary results show that high stress condition has no obvious effects on the propagation law of blasting stress wave or its stress peak in the medium. In addition, it is found that medium in the “elastic vibration area” by conventional blast zoning is not always “elastic,” and on this basis, the concepts of “plastic area” and “quasielastic area” are put forward. The high stress condition does not influence partition range of above “plastic area” or “quasielastic area,” but in the “plastic area,” the high stress condition decreases both plastic strain value and its decay rate of relevant gauging points.