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Basic investigations to establish an ultrasonic stress evaluation technique for aero engine materials

: Hubel, Sebastian; Dillhöfer, Alexander; Rieder, Hans; Spies, Martin; Bamberg, Joachim; Hessert, Roland; Preikszas, Christina

Deutsche Gesellschaft für Zerstörungsfreie Prüfung e.V. -DGZfP-, Berlin:
4th International Symposium on NDT in Aerospace 2012. CD-ROM : November 13-15, 2012, Augsburg, Germany
Berlin: DGZfP, 2012 (DGZfP Proceedings BB 138-CD)
Paper Th.1.B.3, 8 pp.
International Symposium on NDT in Aerospace <4, 2012, Augsburg>
Conference Paper
Fraunhofer ITWM ()
residual stress; ultrasound; titanium; Inconel; tensile test

To satisfy the high demands in view of technical reliability, weight, power, economic efficiency and lifetime of modern aero engines, it is essential to benefit from the full potential of the employed materials. In this respect, residual stresses in the bulk of components are of considerable importance as they have e.g. a strong influence on component distortions during the whole manufacturing process and therefore also on the efficiency of these processes. The measurement of residual stresses using ultrasound in the bulk of materials is a fast and nondestructive method, already well-established for steel components. Thus, the aim of our research was to test whether the ultrasonic stress measurement method is also applicable for nickel- and titanium-based alloys used in aero engine manufac turing. In this contribution we report on basic investigations performed with regard to the achievable measuring effects. In uniaxial tensile tests we determined the time-of-flight sensitivity of different ultrasonic waves in dependence of the applied stresses. Based on these results we have calculated weighting factors describing the correlation between the change in stresses and the change in the velocities of longitudinal waves and of shear waves with different polarization directions with respect to the applied stresses. The test specimens were taken from different regions of a single forging made of Inconel 718. To investigate the effect of texture on the measurement results, some of the samples have been subjected to heat treatments. In our contribution we give a short overview ove r the basic principles of the ultrasonic method, we illustrate the modification and assembly of a high-precision ultrasound time-of-flight measurement system and we analyse the results with respect to future work.