Porous materials have been explored for some time as low-noise trailing edges. At the Institute for Materials Science of Technische Universität Braunschweig, a porous aluminum was optimized for use as a low-noise trailing edge. Experiments suggested that, depending on the rolling parameters, graded compaction occurs in the thickness direction of the rolled material.
The working hypothesis is that graded compaction is due to a gradient in hydrostatic stress during rolling and that the gradient in hydrostatic stress can be controlled substantially by changing the compressed length. An alternative theory is to attribute the gradient in compaction to shear stresses. According to Seuren et al [1], the shape of the gradient in shear stresses depends on the relative compressed length. A series of experiments performed on a porous aluminum (technically pure aluminum A85 according to Russian standard), covering different compressed lengths, was evaluated with respect to its porosity using computed tomography. A publication of these data is in progress.
In addition to the experiments, the material data were determined by means of compression tests and used for the porous material model according to Deshpande et al [2]. In this way, the experiments carried out are reproduced using FE simulation. The experimentally determined porosity values are compared with the data from the simulation. Furthermore, it is verified which shear stress range (according to Seuren [1] et al.) the experiments cover. In this way, it is clarified without doubt whether a gradient in the hydrostatic stress or a gradient in shear stresses is mainly responsible for the densification of the material. Understanding the formation of the gradient can help to further optimize the rolling process for the production of porous trailing edges.

[1]Seuren, S.; Seitz, J.; Krämer, A.; Bambach, M.; Hirt, G. Accounting for shear deformation in fast models for plate rolling. Production 631
Engineering 2014, 8, 17–24. https://doi.org/10.1007/s11740-013-0500-4
[2] V.S. Deshpande, N.A. Fleck,Isotropic constitutive models for metallic foams,Journal of the Mechanics and Physics of Solids,Volume 48, Issues 6–7,2000,Pages 1253-1283,ISSN 0022-5096, https://doi.org/10.1016/S0022-5096(99)00082-4