Laboratory study of wave propagation due to explosion in a jointed medium

Abstract

A digital laser dynamic caustics experimental system is utilized to study the dynamic characteristics of propagation of main cracks and secondary cracks in PMMA medium with flaws under explosion loads. Prefabricated through-cracks are found to open or close as a result of the explosion stress wave reflection from these flaws, which weakens the dynamic behaviors of the main cracks. These main cracks generally do not pass through prefabricated cracks and continue to propagate. Secondary cracks are generated from the ends of the prefabricated through cracks. The initiation and propagation of secondary cracks are caused by the diffraction effect of the tensile stress concentration at both tips of the flaws. The cracking angles of the secondary cracks are closely related to the prefabricated cracks and the incident angle of the explosion stress wave. The secondary cracks initiate from the direction of the maximum energy release rate, and exhibit the mixed fracture mode. The mechanical characteristic values such as the crack length, propagation velocity, and DSIF of main crack that are not directly affected by prefabricated through-cracks are much greater than the values for secondary cracks. Under explosion load, the initiation toughness is from 0.5 to 0.65MN/m3/2, and the arrest toughness is from 0.25 to 0.35MN/m3/2.