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Communication Dans Un Congrès Année : 2018

Unified criterion for fatigue endurance modelling under combined loading: static and vibratory

Résumé

Compressors in helicopter engines are subjected to combined load cycles during a flight mission. They consist of the superposition of static stresses, dynamic stresses, and thermo-mechanical stresses, all originating from independent sources with decorrelated spatial and temporal bases. A conservative local approach is currently used in industries to justify the fatigue endurance of such components with multiaxial and non-proportional stress states. To the authors' knowledge, current fatigue criteria in literature have various limitations when applied to combined cycle fatigue (CCF). This research aims at proposing an approach to downswing the conservatism of the local based approach by appealing to LEFM methods, while also limiting the computational cost of 3D damage tolerance design calculations. The propagation or arrest of a short crack is dependent on the stress function around its crack tip, notably by the stress gradient. This can be determined vis-a-vis an a priori defined zone by analogy to the mode structure of the stress state through the Karhunen-Love procedure (KLP). Second, the fate of a short crack is also dependent on a multiaxial stress function which can also be obtained through KLP. The latter is often a rambling function for high order vibration modes. However, these complex stress functions can be approximated by a summation of simple analytical stress functions, themselves consisting of a non-local and a multiaxial stress function. For each of these functions, LEFM parameters can be calculated and integrated into a short crack non-propagation criteria. The novelty of this research is to project directly a sum of representative analytical stress functions on an industrial geometry vibrating at high order modes and determine whether or not a parametrized crack will propagate. The respective LEFM parameters can be projected on the geometry which does not require fine discretization as in some computationally greedy explicit methods.
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Dates et versions

hal-01903880 , version 1 (24-10-2018)

Identifiants

  • HAL Id : hal-01903880 , version 1

Citer

Bhimal Bholah, Yoann Guilhem, Julien Jaravel, Sylvie Pommier. Unified criterion for fatigue endurance modelling under combined loading: static and vibratory. European Conference on Fracture 22 (ECF22), Aug 2018, Belgrade, Serbia. ⟨hal-01903880⟩
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