Numerical study on crack propagation under explosive loads

Dynamic crack propagation in brittle materials plays an important role in understanding the fracture mechanism. Numerical simulations on crack propagation in the polymethyle methacrylate (PMMA) under explosive loads were carried out through Autodyn 3D code. Although the Johnson-Holmquist (JH-2) constitutive model has been widely treated as an acceptable scheme, it cannot improve the description in the post-failure response of material and reduce the mesh dependency, so the crack softening failure model are introduced in our present work based on two failure criterions. First, material parameters of JH-2 model, failure criterion, and crack softening failure model are determined from available data and calculations. The circular and rectangle thin plates are modeled to explore the fracture mechanisms for single-borehole and dual-borehole explosions. The simulation results well reproduced the entire dynamic evolutionary process of the crushed and fractured zones, crack initiation, propagation and arrest as well as secondary propagation, which successfully proved the reliabilities of the combination of JH-2 constitutive model, failure criterion, and crack softening failure model and corresponding material parameters. For dual-borehole explosion, the crack linkage is well performed when borehole distance L is 20 and 30 cm; cracks are failed to link with each other at L = 40 cm although main cracks have arrived into the opposite fractured zone. More importantly, it is found that the crack linkage mainly depends on L , which has an important effect on linkage style and its location. Despite a larger L makes more difficult in crack linkage, this difficulty lies not in the shortage of crack length, but in losing control of directional fracture of cracks between two boreholes.