16 A. Buljac et al. Fig. 3.1 (a) Schematic representation of the laminography technique with the loading device and CT-like sample; (b) early strain field from slanted region shown together with the position of the final failure illustrated as height map the loading history. Plane strain conditions in the crack propagation direction predicted in numerical simulations [15] have been confirmed by kinematic measurements [13] while through thickness equivalent strain distributions varied significantly. Slant strained bands appeared well before damage, i.e. plastic flow is very heterogeneous before any significant signs of void nucleation and growth is measured at micrometer resolutions. The origin and observed behavior (i.e. activation and deactivation) of strained bands at the microscale still remains unclear. The T8 heat treatment induces relatively high yield stress followed by low work hardening. Low work hardening materials are believed to be prone to flow localization [16]. Following the same logic, strong work hardening materials should be more resistant to the flow localization. However, this was not the case for another aluminum alloy (i.e. AA2139 T3). Numerous strain bands were observed. Their intermittent activity and pattern were two key findings [14]. Further, damage set in very late during loading. Since these two alloys were different, the question remains open for AA2139 with T8 treatment and AA2198 under T3 condition. The latter is studied herein. 3.2 Kinematic Fields and Damage Micromechanisms In this work, results obtained for a CT-like specimen made of AA2198 T3 are presented. The T3 heat-treatment results in a microstructure responsible for a strong work hardening behavior, which is the key feature for conducting such analyses. Strong work hardening and high strains to failure indicate low level damage development and subsequent late softening phases. Logically, this should be promoted by homogeneous strain flow with less strain heterogeneities. Hence, the strain fields in this high work hardening material are analyzed in the work. Moreover, since similar analyses exist for the T8 heat-treatment [11], the influence of the latter is also studied. The strain fields and damage micromechanisms in the slant region 1 mm from the notch root as well as in the region closer to the notch root are presented in the work. Despite strong work hardening, the slant strained bands occur early on in the loading history before any signs of damage onset. Interestingly, void growth inside and outside the bands does not differ
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