Mechanical Properties of Shark-Skin Like Structured Surfaces for High-Temperature Applications

Abstract

Structuring surfaces with so‐called riblet structures shows improvements in drag reduction in external turbulent fluid flows. This paper presents the result of collaboration between four research groups which focused on the transferability of the riblet approach to high temperature material systems. With respect to the application excellent mechanical properties and high temperature oxidation resistance of the riblets are necessary. Different strategies for riblet fabrication are presented. Applicable processes as halogenation, coatings fabrication and laser ablation followed by oxidation to process “tiny” riblets on relevant material systems for aero engines such as Ni‐based super‐alloys (IN718, PWA1483) or titanium aluminides (gamma‐TiAl e.g. TNMB1) are presented. Not only that the riblets were fabricated on 2 different substrates, they also have different compositions such as metallic, half and completely oxidised. The riblet morphology is characterized and principle studies of the mechanical stability outlined promising results. The focus lies on the riblet characterization, so that the maximum applied stress is substrate specific and limited by the complete failure of the structures (e.g. cracking and deviation from the initial dimensions). All tested riblets exhibit good bonding to the substrate (i.e. partial riblet flanking). Results of quasi cyclic four point bending tests and low cycle fatigue are discussed taking into account the differences between the riblet and the substrate composition.