Study on mechanism of oblique incident explosion stress wave on directional motion crack

Abstract

The interaction between explosion stress waves and cracks in engineering blasting is a complex and critical issue. The mechanism of an obliquely incident explosion stress wave on directional crack motion is intricate, involving extension, deflection, and changes in fracture patterns. The mechanical effects of an obliquely incident explosion stress wave on a crack are examined through theoretical analysis, dynamic caustic experiments, and numerical simulations. The results indicated that the oblique incidence of an explosion stress wave causes significant caustic speckle distortion at the crack tip, with the deformed caustic speckle shape differing distinctly from the circular caustic speckle characteristic of a type I crack. The stress intensity factor and crack growth rate at the crack tip decrease sharply under the compressive stress in the bright region of the explosion stress wave. They rise rapidly under the influence of tensile stress in the dark area. The caustic speckle of Ⅰ+Ⅱ compound cracks is generated at the crack tip by an oblique incident explosion stress wave, and the variation patterns of type I and type II stress intensity factors (K_Ⅰ and K_Ⅱ) are opposite. When the stress wave reaches the crack tip, there is a reduction of 50 %, 69.2 %, and 88.5 % in the minimum peak value of stress intensity factor for specimens S-2, S-3, and S-4 respectively compared to simultaneous initiation. Furthermore, there is a decrease of 23.9 %, 34.8 %, and 47.8 % in the maximum peak value；The minimum peak speed is reduced by 27.5 %, 50 %, 80 %, and the maximum peak speed is reduced by 11.4 %, 17.1 %, 28.6 %. A specific functional relationship exists between the stress wave’s incident angle and the crack’s deflection length. The change of a single variable does not determine the crack propagation length and direction; instead, they are affected by three variables: the incident angle of the stress wave α, σ₁, and σ₂. After the explosive detonation, the compressive stress zone first acts on the crack tip element, resulting in a negative stress field. Then, the tensile stress zone acts on the crack tip element, and the stress field becomes positive. Under the alternating influence of tensile and compressive stress, the stress field exhibits a “positive and negative alternating” pattern and a downward trend. The stress in the x and y directions decreases by 31.8 %, 45.5 %, and 59.1 % and 27.6 %, 40.7 %, and 57.2 % respectively when the explosion-induced stress wave reaches the crack tip, compared to simultaneous initiation. Investigating the mechanism of the oblique incident explosion stress wave on directional motion cracks is beneficial for understanding the interaction between explosion stress waves and cracks and provides a theoretical foundation and technical support for crack control in engineering blasting.