The importance of impact problems has led to extensive research work over the years. In an impact phenomenon, the material is subjected to very short duration high force levels resulting in large plastic deformations and significant temperature rise. One of the most common phenomena of the impact problem is the occurrence of fracture. Fracture occurs when the velocity of impact is very high. In metal, it will lead to ductile fracture. Ductile fracture generally takes place due to void nucleation, then the growth of the nucleated voids and at last voids coalescence to form a micro-crack. A number of studies on ductile fracture and damage simulation in static condition have been carried out using this approach. But, there is a limited study on the prediction of fracture in impact problems. In impact problems, the effects of strain rate, stress triaxiality, and temperature on material behavior become significant. In the present work, damage growth, and effect of high strain rate are studied for ductile fracture during the high-velocity impact of cylindrical tubes using commercial finite element (FE) software ABAQUS/Explicit using continuum damage mechanics (CDM). It is shown that CDM-based modeling is able to capture the failure of the tubes.

Impact problems are an important class of problems usually accompanied by large deformations and sometime fracture of the impacting bodies. In many fields such automotive crashworthiness analysis and design, turbine design, metal forming problems etc. one has to invariably consider the possibility of fracture and study its effect on the component/structure. Fracture in these applications is mostly happens after considerable plastic deformation and is referred to as ductile fracture. A lot of research work has being carried out in the area of ductile fracture under impact loads. Recently, a new coupled elasto-plastic damage model for ballistic applications incorporating effect of Lode angle in the Johnson and Cook failure criterion using a Lode angle dependent function has been proposed. In the present work, this model is employed to study the ductile fracture of tubes impacted against a rigid surface using Abaqus/Explicit through a user input subroutine VUMAT. The effect of Lode angle on the fracture pattern is studied. It is shown that the Lode angle significantly affects the failure pattern.

Study of impact problems is of great interest in many engineering fields, such as automotive industry, aircraft industry, defense industry etc. Orbital debris impact on space station, crash-worthiness of automobiles etc. are few examples of impact problems. Impact problems are characterized by short duration, large plastic deformation, high strain rates, rapid dissipation of energy, thermal softening etc. Contact-impact problems like crash-worthiness of vehicles, impact testing etc often involve ductile fracture. Ductile fracture is a mode of failure in which voids either pre-existing within the material or nucleated during deformation grow until they link together or coalesce to form a continuous fracture path. The continuum damage mechanics model of Lemaitre is one of the most commonly used approaches to study ductile fracture. A number of studies on damage growth and fracture simulation, in static processes have been carried out using this approach. However, number of such studies on the prediction of fracture in impact problems are limited. In the present work, damage growth, and effect of high strain rate are studied for ductile fracture during high velocity impact of cylindrical tubes using commercial finite element software ABAQUS/Explicit.