Previous research has shown that porous material as a trailing edge of an aircraft’s wing can cause major reduction of noise generated by the circulation of air around the airframe. It has been shown that the transition from solid to porous material leads to additional noise, thus a graded transition is to be preferred. Furthermore, every edge in the direction of flow, in this case the ligaments of the porous material, may lead to additional noise. Therefore, porosity needs to be graded and pores need to be stretched into the direction of flow.
In this study, a promising technique to adapt pore structure and porosity by cold rolling of porous material with regards to the application as a low noise trailing edge is shown. The experiments were performed using a sintered fiber felt consisting of a supporting grid (wire mesh) and the functional layer (sintered, randomly oriented fiber mesh). A rolling mill with a gap between rolls which can be adapted during rolling is used to modify the pore structure of the material. This allows to gradually densify the porous material in the direction of rolling. Furthermore, a superimposed tensile stress can be applied during rolling by attaching the material to a hydraulically operated pull out table. This is used to enhance the elongation of pores in the direction of rolling. The characterization of the pore morphology before and after the rolling process is carried out using three dimensional computer tomography combined with a line segmentation technique. Additionally, the mechanical properties are characterized using tensile tests. The combination of CT-analysis and mechanical testing is used to clarify the influence of cold rolling, particularly with the described features, on the pore structure, porosity and mechanical properties of the material.