New measurement approach for determination of residual stress and cold work at surface treated aeroengine materials

Speaker:
Köhler, Bernd; Fraunhofer IKTS; Germany

Authors:
Köhler, B.; Fraunhofer Institute for Ceramic Technologies and Systems IKTS; Germany
Kissing, J.; MTU Aero Engines AG; Germany
Gartsev, S.; Fraunhofer Institute for Ceramic Technologies and Systems IKTS; Germany
Barth, M.; Fraunhofer Institute for Ceramic Technologies and Systems IKTS; Germany
Rjelka, M.; Fraunhofer Institute for Ceramic Technologies and Systems IKTS; Germany
Bamberg, J.; MTU Aero Engines AG; Germany
Hessert, R.; MTU Aero Engines AG; Germany

ID: ECNDT-0359-2018
Download: PDF
Session: Materials Characterization UT
Room: G1
Date: 2018-06-13
Time: 16:20 - 16:40

Aero Engine materials are exposed to high temperatures and high stresses in operation. To increase the fatigue strength, the surface is treated by shot peening, laser peening or deep rolling. These processes introduce compressive residual stress and structure modifications (cold work) in a near surface layer. There are several attempts to determine these advantageous surface property gradients nondestructively. The applied methods include eddy current and Rayleigh waves velocity measurements. Recently the application of the Hall-effect was also proposed. Besides selectivity, all these methods lack of good sensitivity. A very small change in a large signal has to be measured reliably; a big challenge for a method, supposed to be applied in a harsh repair shop environment.
The here proposed new method builds up on Rayleigh wave propagation through a straight line between a surface treated and a non-treated area. Even a slight change of sound velocity between both regions lead to significant refraction effects for the wave paths with near grazing incidence. The wave propagation is visualized for such cases by laser vibrometer measurements. Moreover, the following is demonstrated: when the incidence angle to the border line in a pitch catch arrangement is varied, significant transmission drops of up to 30 % are observed. This comprises a very solid measurement effect. Possible arrangements for future practical applications are discussed.