Prediction of fragmentation and experimentally inaccessible material properties of steel using finite element analysis

High strain-rate properties of materials are needed for predicting material behavior in extreme environments. The demand for high strain-rate properties continues to increase for commercial and military applications as the operating environments become more extreme, such as fragmentation, impact and explosions. To reduce time and expense, Finite Element Analysis (FEA) is being used to simulate these behaviors and reduce the number of experiments needed to characterize how a material performs at high-strain-rates. A finite element model for predicting fragmentation behavior of a high strength steel ring was developed using Abaqus Computer Aided Engineering (Abaqus) software. AISI 4340 steel, a low alloy Cr-Ni-Mo steel, was used in the analysis. The results of the finite element model were compared to the results from CTH, a two-dimensional Eulerian shock physics hydro-code. CTH was also used to develop a transient loading curve for the Abaqus model. The fracture strain in the model was adjusted to induce failure in the ring. Element deletion was used to model failure. A fracture strain less than 1×10-5 was needed to initiate fragmentation. The effects of mesh type and model defects were also investigated. A fracture strain of 1×10-5 was found to initiate fragmentation of AISI 4340 steel leading to element deletion.The pressure loading profile can greatly influence the fragmentation behavior.Meshing procedures have a significant effect on the fragmentation behavior and the von Mises stress (tetrahedral mesh vs. brick mesh).Quadratic tetrahedral elements predict much higher stresses near the surface of the ring.Stress predictions during fragmentation is highly dependent on the distance from a newly deleted element.