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Crack propagation in layers under small-scale yielding

J.P. Vafa, S.J. Fariborz

2016
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Procedia Structural Integrity
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During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation
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... mpany, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a model can be useful in the goal of predicting turbine blade life, given a set of FDR data. Abstract The stress field is obtained in an isotropic elastic layer containing an edge dislocation. The dislocation solution is used to derive integral equations for a cracked layer. These are a set of Cauchy singular integral equations which are solved numerically for the density of dislocations on a crack surface. The density of dislocations is utilized to determine stress components in the vicinity of a crack tip. The stress field contains singular as well as non-singular terms. Assuming small scale yielding, the von-Mises yield criterion is adopted to define a plastic region around a crack tip under the plane-stress situation. Several examples are solved and the plastic region developed by a crack with different orientations and loadings is specified. Moreover, in another example, plastic regions around the tips of two interacting cracks are defined. The geometry of the plastic regions is utilized to obtain a crack propagation angle. Abstract The stress field is obtained in an isotropic elastic layer containing an edge dislocation. The dislocation solution is used to derive integral equations for a cracked layer. These are a set of Cauchy singular integral equations which are solved numerically for the density of dislocations on a crack surface. The density of dislocations is utilized to determine stress components in the vicinity of a crack tip. The stress field contains singular as well as non-singular terms. Assuming small scale yielding, the von-Mises yield criterion is adopted to define a plastic region around a crack tip under the plane-stress situation. Several examples are solved and the plastic region developed by a crack with different orientations and loadings is specified. Moreover, in another example, plastic regions around the tips of two interacting cracks are defined. The geometry of the plastic regions is utilized to obtain a crack propagation angle.

doi:10.1016/j.prostr.2016.06.430
fatcat:mmgc6qg7rreh3ppcgj23xn2jle