Evolved eggshell strength is greater in several lineages of obligate avian brood parasites (birds that lay their eggs in other species’ nests) compared to their hosts. Greater strength is typically indirectly implied by eggshell thickness comparisons between parasites and hosts. Nevertheless, there is strong evidence that the eggshell structural organization differentially influences its mechanical properties. Using instrumental puncture tests and SEM/EBSD and XRD techniques, we studied the most relevant eggshell mechanical, textural, ultra- and microstructural features between several host species and their parasitic cowbirds (Molothrus spp.) that display different egg destructive behaviors reducing host reproductive fitness, and include the more frequently host-egg puncturer M. rufoaxillaris and M. bonariensis, and the host-egg remover M. ater. The results, analyzed using a phylogenetic comparative approach, showed interspecific patterns in the mechanical and structural features. Overall, eggshell of both species of the two egg-puncturer parasites (but not of M. ater) were stronger, stiffer, and required greater stress to produce its fracture than the respective hosts’ eggs. These features were affected by eggshell micro- and ultrastructures, related to the increased of the intercrystalline boundary network acting in cooperation with the increased of the palisade layers' thickness. Both of these structural traits generate more options and greater lengths of intercrystalline paths, increasing the energy consumed in crack or fissure propagation. The reported patterns of all these diverse eggshell features support a new set of interpretations, confirming several hypotheses regarding the impacts of both reproductive strategies (parasitic vs. parental) and parasitic egg destruction behaviors (more vs. less frequently puncturing).

We study the deformation inducing heterogeneity in an Aluminum alloy 6063-T6 in the form of a sheet processed at room temperature by Equal Channel Angular Sheet Extrusion (ECASE) up to a maximum equivalent strain of 1.86 following route C. The through thickness strain distribution showed higher strains in the edge vicinities than in the sheet core. The texture was heterogeneous between the edges and the sheet core with a strong Cube component in the initial deformation stages, and a rolling texture with the S component in the sheet edges. Different microstructural characteristic, like grain size, average misorientation and fraction of High Angle Grain Boundaries (HAGB) decreased by increasing the deformation. The Geometrically Necessary Dislocation (GND) calculations corroborated the existence of a heterogeneous microstructure along the sheet thickness, giving rise to gradients of plastic deformation which allowed to obtain a good strength-ductility relationship. It was demonstrated that ECASE process was a good alternative to produce heterogeneous microstructures. The material heterogeneity was found not to be randomly distributed across the sheet thickness but rather showing higher dislocation concentration and bigger grain size reductions in the edge's vicinities than in its middle zone.

The current work presents the results on Mg AZ31B alloy sheets subject to four passes using Equal Channel Angular Sheet Drawing (ECASD) at various temperatures (25, 100, and 200 C). Textures are determined by laboratory X-ray diffraction and EBSD. EBSD allows the evaluation of the evolution of crystal sizes in function of the distance to the surface and the presence of twinning. Twinning is evident by the analysis of the textures, which show mainly two components, one due to the spin induced by the shearing of ECASD and the other one as a direct product of twinning. Micro-hardness, by Knoop tests on the lateral face of the sheets, are performed, allowing the determination of the influence of SPD on the hardness from surface to surface, going through the center of the sheet. Almost 50% increase on hardening, with respect to the non-processed material, is obtained near to the surface after four and six passes. The effectiveness as a hardening technique declined after the first four passes.