Modelling the sources of cracking of aircraft compressor vanes rings

Nash, D.H. and Dempster, I. (2005) Modelling the sources of cracking of aircraft compressor vanes rings. Engineering Failure Analysis, 12 (5). pp. 699-710. ISSN 1350-6307 (http://dx.doi.org/10.1016/j.engfailanal.2004.12.01...)

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Abstract

Aircraft engines are, by definition, designed for high service life duty. However as part of in-service maintenance, some components have shown, upon inspection, wear and localised cracking thus requiring repair or replacement. An understanding of the source of stress or loading is required in order to assess the effect of the crack, to see if further propagation will result. Such cracks have been found on a compressor vane ring associated with a turboprop engine. It is necessary to establish the origin of the stresses that have been leading to cracks and subsequent failures observed throughout the component. Due to the complexity of the shape of the component, a finite element approach was adopted and the component modelled and analysed for a series of representative load cases. The results and outcomes are presented herein. In addition, some guidance is given on the construction, development and verification of a three dimensional finite element model for use in compressor vane design. The stresses in the compressor vane ring arise from pressure and thermal actions, with the thermal action generating the highest stresses. However, in order to determine the magnitude of the thermal loading, some in-service experiments were undertaken using a full size test engine. Thermal characteristics were established using a thermal paint and suitable calibration specimens. Thereafter, these loads were applied to the finite element model of a single blade and thereafter the entire ring. The largest thermal transients occur during start-up and shutdown, along with the full power condition, which may happen during flight. Each of these cases was analysed as part of a full thermal parameter study. In each case, the location, magnitude and direction of the maximum stresses was recorded and comparisons made with the damage observed in the real structure. As a result, some recommendations have been made on the design and approach to repair of the vane ring for improved service life performance.

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