Research on protective mechanism of semicircular arc pre-crack under impact load.

• The pre-crack initiates anew when the horizontal distance between the moving crack and the semicircular arc pre-crack is small. When the distance increases to 8.33 mm, the crack no longer penetrates the semicircular arc pre-crack, and the pre-crack attracts the crack first and then repels it. When d = 11.67 mm, the pre-crack has no considerable effect on the moving crack. • The crack deflection angle and the horizontal offset distance of the two groups of experiments conform to a linear function. • Setting the semicircular arc pre-crack outside the protected medium can effectively protect the medium from impact load. When the moving crack is outside the arc, the medium inside the arc pre-cracks are in the stress relief zone, which can be well protected. In this paper, a plexiglass (PMMA) specimen is designed for dynamic impact testing based on the digital laser dynamic caustics experimental system. The impact of offset distance on dynamic fracture behavior of PMMA specimens with semicircular arc pre-cracks in two different directions is investigated. Research shows that: the pre-crack initiates anew when the horizontal distance between the moving crack and the semicircular arc pre-crack is small. With the increase of horizontal distance, the pre-crack attracts the crack first and then repels it. When the distance reaches a critical threshold, the pre-crack has no considerable effect on the moving crack. The above conclusions are not affected by the direction of the semicircular arc pre-crack. Furthermore, the crack deflection angle and the horizontal offset distance of the two groups of experiments conform to a linear function. When the horizontal offset distance is small, the middle part of the pre-crack initiates again. When the moving crack is outside the arc pre-crack, the medium in the pre-crack is the stress relief zone, according to the numerical data. The ability of the medium to resist impact damage can be effectively boosted by placing acceptable pre-cracks on the medium's periphery. [ABSTRACT FROM AUTHOR]