Microplane Model for Steel and Application on Static and Dynamic Fracture

Abstract

The behavior of materials and structures is strongly influenced by the loading rate. Compared with quasi-static loading structures loaded by high loading rate and impact acts in a different way. First, there is a strain-rate influence on strength, stiffness, and ductility, and, second, there are inertia effects activated. Both influences are clearly shown in experiments. Although steel does not exhibit significant strain rate sensitivity, the dynamic fracture of steel is highly sensitive on loading rates. In this paper, the static and dynamic fracture of steel is numerically studied on a compact tension specimen (CTS), which is loaded under loading rates up to 100 m/s. First, the proposed microplane model for steel is discussed and verified for monotonic and cyclic quasi-static loading. Subsequently, three-dimensional (3D) finite element dynamic fracture analysis is carried out. It is shown that the resistance of steel (apparent strength and toughness) increases progressively after the critical strain rate (approximately 100/s) is reached. Moreover, the crack branching phenomena and significant decrease of ductility are observed. The phenomena that are also well known from experimental evidence are attributed to the effect of structural inertia and inertia related to the high nonlinear behavior of steel at the crack tip and in the plastification zone. The numerical results indicate that maximum crack velocity of steel is much lower than the Rayleigh wave velocity, and for the investigated steel, it reaches approximately 400 m/s.