A Modeling Approach to Predict Fretting Fatigue on Highly Loaded Blade Roots

Abstract

Article Number: 082101International audienceA lifing technique for predicting fretting fatigue on highly loaded blade-disk attachments has been developed and calibrated. The approach combines extensive testing on nickel and titanium based alloys using a specially devised multiaxial fretting test machine and an analytical lifing procedure, based on finite element contact calculations and multiaxial shakedown fatigue models. In order to reproduce realistic operational conditions and standardize testing conditions, a special fretting fatigue testing machine with high temperature testing capabilities was developed. The machine was employed to perform systematic testing under prescribed load and displacement conditions at representative temperatures. Making use of FEA, the rig test results were calculated to identify relevant parameters such as friction coefficient, slip conditions, and machine compliance. The computation procedure involves the calculation of several major loading cycles until a stabilized response of the structure is achieved. The material response is assumed to be elastoplastic, and a nonlinear friction law (space and time) was applied. From the computed mechanical variables, several life prediction models are benchmarked to establish their capabilities to predict fretting fatigue life. Finally, a most promising life estimation procedure was applied to predict life in a real compressor blade-disk attachment. Predicted failure location and number of cycles to failure are compared against engine test results. The experimental-analytical approach has the potential to predict fretting fatigue risk during the design phase on highly loaded joints, as well as estimating the preventive overhaul intervals for parts already in service

Computational fretting fatigue maps for different plasticity models

“…We have previously used a more refined and converged mesh for the pad and the substrate. 12 The aim here is to perform a parametric study by varying the friction coefficient μ, the normal load P and horizontal displacement δ within the ranges given in Table 2. As 1680 simulations are performed and in order to keep computations in reasonable time, we opted for a coarser mesh, especially for the pad considered as elastic.…”

“…This is not the case for the substrate that is the object of the analysis in this paper. The element size of the mesh used is compatible with that of the process volume found by Amargier et al 36 or the relevant representative volume element (RVE) used for fatigue life estimation by Wackers et al 12 The accuracy of the refined mesh can be checked in different ways. If the solution remains in the elastic regime, a direct comparison with closed-form solutions proposed for instance in Refs [41][42][43] can be performed.…”

“…In the present elastoplastic analyses, we choose an element size of 16 μm, which is of the order of the fatigue RVE size. 36,12 The boundary conditions are defined by the following: (i) a normal load ÀPē y and (ii) a reciprocating horizontal displacement varying between 0 and δ alongē prescribed on the upper surface of the pad (ē x andē y are, respectively, unit vectors along the x and y directions, Fig. 1).…”

“…And therefore, both researcher and engineers rely more and more on complex finite element computations both for the understanding of the phenomena and for the lifetime predictions on structures. [12][13][14][15][16][17] In a recent work, Ambrico and Begley 18,19 studied how different cyclic shakedown regimes are reached in the case of a fretting problem defined by a sphere in contact with a plane. They compared the solutions obtained by the finite element method (FEM) using different elastoplastic material behaviours.…”

“…Under the assumption of a lifetime defined by a crack initiation, the Dang Van fatigue criterion is one of the successfully applied fretting fatigue criteria. 13,[31][32][33]15,34,12 This multiaxial criterion is based on the shakedown concept and a multiscale homogenisation scheme. Its relation to crack initiation phenomena related to mixed stick-slip regime of fretting was discussed in Refs [32,33].…”