Dynamic Fracture and Fragmentation

Abstract

The dynamic fracture and fragmentation of a solid body or structure can result from the application of an intense impulsive load. The scale of such events ranges from shaped-charge jet breakup and rock blasting to astro-physical impacts and creation of planetary debris. In rock blasting, for example, specific information on ejecta velocities and fragment size distributions is sought, and methods to control resulting fragment sizes by proper placement and type of explosives are of interest (Grady and Kipp, 1987). In stretching shaped-charge jets, fragmentation characteristics, such as time-to-breakup and particle size are intimately tied to performance (Chou and Carleone, 1977). Ejecta from planetary and meteoric impact provide information on the evolution and dynamics of the solar system (Melosh, 1984). The applications in which solids or structures are subjected to intense dynamic loading and when breakup must be mitigated or controlled are numerous and varied. The need to understand the dynamic fracture mechanisms for such applications has provided the impetus for research in this rich area, and the field is currently quite active. The response of a single crack or void, within a solid body, to both static and impulsive loading has received considerable attention over the past several decades and is reasonably well understood (Freund, 1973; Chen and Sih, 1977; Kipp et al., 1980). The mechanics of a system of cracks or voids under impulsive or stress-wave loading, and how the cooperative response of such a system relates to the transient strength and ultimate failure and fragmentation of a solid body is less well understood, and has been a subject of study over the past decade (Curran et al., 1977; Davison and Graham, 1979; Meyer and Aimone, 1983; Grady and Kipp, 1987; Curran et al., 1987). Experimental studies of fracture under high-rate loading have revealed unusual features associated with the phenomenon, such as enhanced material strength and failure-stress dependence on loading conditions. Although such observations have led to the postulation of rate-dependent material properties, most of the features can be understood through fundamental fracture concepts when considered in terms of a system of interacting cracks or voids.