Dynamic crack nucleation, propagation, and interactions with crystalline secondary phases in aluminum alloys subjected to large deformations

Abstract

The major objective of this work was to model within a continuum framework the dynamic nucleation and evolution of failure surfaces in aluminum alloys with complex microstructures, using a recently developed compatibility-based fracture criterion for large deformations. Computational analyses were conducted to understand how Mn-bearing dispersoids, Ω and θ′ precipitates affect dynamic fracture processes in an Al–Cu–Mg–Ag alloys (2139-Al). High strain-rate simulations were based on a rate-dependent dislocation-density-based crystalline plasticity formulation and a nonlinear explicit dynamic finite-element approach. Results indicate that the fracture criterion elucidated how dispersoids and precipitates have a dominant role in dynamic crack blunting, branching and arrest. Rationally orientated precipitates result in overall dynamic microstructural strengthening and enhanced uniformity of deformation. These precipitates, however, accelerated unstable crack propagation, and this is amplified in the presence of a pre-crack. In contrast, dispersoids decreased microstructural toughness and ductility, but greatly improved dynamic damage tolerance, especially in the presence of a pre-crack. It can also be predicted that low angle boundaries can change the propagation direction of ductile cracks, and contribute to damage tolerance without crack initiation. Collectively, rationally oriented precipitates and dispersoids can significantly improve the combined dynamic strength, toughness and damage tolerance of crystalline aluminum alloys.

Keywords:

• aluminum alloy
• crack nucleation
• deformation
• dynamic fracture

Acknowledgments

Support from the U.S. Army Research Office Grant No. ARO W911 NF-06 1 0472 is gratefully acknowledged.