Abstract
In this study a procedure to stress intensity factors calculation for imitation models made of titanium alloy is described. In service fatigue cracks are detected in a disk and blade “dovetail type” attachment. On the base of this attachment dimensions and with taking into account the biaxial loading conditions of rotating compressor disk the two geometries of imitation model of gas turbine engine compressor disk are developed. To accurate verification of biaxial loading conditions, the first imitation model of constant thickness is used. In order to fully reproduce the geometry of the compressor disk and conditions of mixed mode crack growth, the second imitation model with reduced cross section is proposed. The fatigue crack growth experiments of imitation models were carried out at room temperature on a biaxial testing machine. Two different stress ratio values are applied several times to each imitation model in order to fix the experimental crack front positions. The elastic and plastic stress intensity factors used for the representation of the experimental results are computed by using full-size 3D Finite Element analysis of the imitation models with surface quarter elliptical and through-thickness cracks.
Highlights
M anufacturing flaws, mechanical damages, pre-cracks and crack initiations due to cyclic loading often lead to undetected crack propagation in commercial structures, e.g. in aircraft components
This paper provides the determination of elastic and plastic stress intensity factors (SIFs) for various crack sizes obtained by experiments on biaxially loaded imitation models and establish the advantages of integrating numerical analyses and experimental research for verification and development of modern crack growth rates and lifetime prediction models
In order to fully reproduce the geometry of the compressor disk and the conditions of mixed mode crack growth, the imitation model II with reduced cross section is proposed (Fig. 2b)
Summary
M anufacturing flaws, mechanical damages, pre-cracks and crack initiations due to cyclic loading often lead to undetected crack propagation in commercial structures, e.g. in aircraft components. Shanyavskiy [12] shows that the predominant failure mechanism for gas turbine disks is the low cycle fatigue (LCF) resulting in the formation of a fracture relief that reflects the two-phase (α+β) lamellar structure of the titanium alloy, and a fragmentary fatigue striation formation Such loading conditions lead to fatigue crack initiations and their propagation up to a critical zone in rotating disks. In the case of nonlinear cyclic deformation, damage accumulation, growth, and the fatigue life of structural components are underestimated by the numerical procedure This is due to the simplified axis symmetric modeling and the choice of the elastic crack growth constants, and due to the change in mixed-mode loading conditions along crack fronts at operation. This paper provides the determination of elastic and plastic SIFs for various crack sizes obtained by experiments on biaxially loaded imitation models and establish the advantages of integrating numerical analyses and experimental research for verification and development of modern crack growth rates and lifetime prediction models
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