Penetrator Case Fracture Predictive Technoiogy: Volume 1-Dynamic Fracture Mechanics Methodology

Abstract

Abstract : A dynamic fracture mechanics methodology has been implemented into the Lagrangian finite element hydrocode EPIC. The generalized energy release rate T* was assumed to be a measure of the crack driving force. This representation for the crack driving force was selected because its generality includes elastic plastic behavior and inertial effect. In addition to the introduction of the crack driving force, a nodal release algorithm to model the formation of traction free surfaces produced by a propagating crack was incorporated into EPIC. The dynamic fracture mechanics enhanced EPIC code was used in the generation phase mode to deduce be dynamic fracture toughness from measurements made during high loading rate fracture tests of AISI 4340 and AP 1410 steel specimens. The internal consistency of the approach and algorithms was demonstrated by performing application phase analyses of these fracture tests to predict the crack growth history. A second set of experiments was devised. using a different experimental arrangement and specimen geometry, to demonstrate the predictive capability of the methodology. A new dynamic test method was developed referred to as a dynamic three point bend test-in which an instrumented, precracked three-point tend specimen is dynamically loaded through a transmitter bar that is struck by a striker bar fired from a gas gun. The length and slated of the striker bar control the duration and intensity of the loading pulse. A finite element model of the experiment was developed. Numerical predictions, using the fracture toughness determined from the independent coupled pressure bar tests, are in relatively good agreement with measured crack growth and strain gage histories, thereby validating the dynamic fracture mechanics computational methodology implemented into EPIC.