Abstract
The mechanisms leading to fracture of aluminum alloy AA2024-T3 under shear loading are investigated via X-ray synchrotron laminography. A 1mm-thick flat double-gage section shear specimen is loaded inside a synchrotron X-ray beamline. The microscale defects population is reconstructed on six loading steps as well as on the broken specimen. The material exhibits an initial void volume fraction of 0.7% as well as a high concentration of large Cu-rich intermetallic particles. Using 2D Digital Image Correlation of projected volume data, based on the void contrast, it is possible to track the evolution of both types of mesoscale defects throughout the loading and to correlate the deformation mechanisms with the local strains. Upon mechanical loading, pre-existing voids rotate and elongate following the deformation of the aluminum matrix. The intermetallic particles fail at early loading stages in a brittle manner, leading to the nucleation of voids normal to the maximum principal stress direction. The newly-created voids continue to grow during the subsequent loading steps impeded by the fragmented particles, eventually forming micro-cracks. A fracture mechanism is proposed based on these observations and assessed with a representative volume element simulation, pointing towards the formation of a shear localization band during the final loading step.
Highlights
After half a century of research on ductile fracture, it is widely accepted that void nucleation, growth and coalescence are the main mechanisms leading to the ductile fracture of polycrystalline metals (e.g. [1])
Most research in the field focused on the important effect of the stress triaxiality, while it is only recently that the second variable characterizing the stress state, that is the Lode parameter, received significant attention (e.g. [4,5,6])
Due to the unstable rupture in combination with the applied in situ load increments, the actual fracture displacement could not be obtained
Summary
After half a century of research on ductile fracture, it is widely accepted that void nucleation, growth and coalescence are the main mechanisms leading to the ductile fracture of polycrystalline metals (e.g. [1]). After half a century of research on ductile fracture, it is widely accepted that void nucleation, growth and coalescence are the main mechanisms leading to the ductile fracture of polycrystalline metals Ductile failure is a process in which plastic deformation promotes the progressive damage of solids all the way until fracture initiation. The seminal works of McClintock [2] and Rice and Tracey [3] showed the pronounced dependence of the ductile failure process on the stress state. Most research in the field focused on the important effect of the stress triaxiality, while it is only recently that the second variable characterizing the stress state, that is the Lode parameter, received significant attention Phenomenological models have emerged that describe the dependence of ductile fracture on both the stress triaxiality.
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