Abstract
In previous study, the authors reported the experiment for dynamic crack branch which arises under quasi static load. From the experimental results, the dynamic crack branch condition (Φtotal criticality theory) was derived. The Φtotal criticality theory means that crack branch arises when the energy flux to crack tip per unit time reaches a steady value of material. Furthermore, the numerical simulation using the moving finite element method was performed, and it has succeeded in mechanical prediction of the crack propagation path after crack branching. This crack branching is observed under quasi static load, and the validity of the Φtotal criticality theory under impact load is not discussed until now. In this study, the crack branching phenomenon under impact load was photographed using ultra high speed camera, and the moving finite element analysis is based on the experimental result. The Delaunay automatic triangulation is used for updated mesh subdivision with crack propagation. In numerical simulation, dynamic J integral is evaluated from path integration around crack tip. Then, Φtotal history with crack propagation is discussed by comparison of experimental results and numerical results. The result has confirmed that Φtotal criticality theory is also recognized in dynamic crack branch under impact load, and that Φtotal critical value of PMMA is about 11 MN/s.
