Estimation of fatigue margins for composite parts of aircraft engine on the base of vibration tests

Abstract

During the modernization of the low-pressure compressor of the regional aircraft engine, a flow separator made of polymer composite material was developed, which has less weight, is easier and cheaper to manufacture. However, the separator must undergo a series of tests before being installed on the engine, in particular the endurance tests, necessary to assess the fatigue strength margin. A method for determining the endurance limit of a large part of an aircraft engine is developed in the presented work and consists in replacing the tests of the entire separator with tests of individual structural elements cut from the part. The shape, dimensions and fixation of the elements have been chosen in such a way that their own test frequency was close to the natural frequency of the flow separator on the engine. The natural oscillation frequencies and places of maximum dynamic stresses have been determined before testing on three-dimensional models of the flow separator and elements cut from it. As a result, the structural elements have been tested until appearance of fatigue cracks which allowed to assess the endurance limit and evaluate fatigue strength margin of the separator.

Application of Composite Materials in an Upgraded Engine Low-Pressure Compressor for a Regional Passenger Aircraft

“…The model and boundary conditions of the calculations of the FS and IP are described in [17] and [18], respectively.…”

“…In order to reproduce fixation at the engine, the special adopter was designed for a fatigue test of the FS using a powerful vibrator [17].…”

“…In order to carry out fatigue tests above the endurance limit of a material, it was suggested to carry out tests of the structural elements cut from FS, instead of the testing the whole separator. The test procedure is described in detail in [17].…”

“…The results of the FS calculations are described in [17]. The static calculation of the FS has not been performed, due to low level of expected static stress for the axisymmetric separator.…”

“…Based on the results of the preliminary calculations, a series of fatigue tests were carried out on structural elements cut from the FS. The test procedure is described in [17].…”