Obtaining the J-integral by diffraction-based crack-field strain mapping

S.M. Barhli, L. Saucedo-Mora, C. Simpson, T. Becker, M. Mostafavi, P.J. Withers, T.J. Marrow
2016 Procedia Structural Integrity  
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
more » ... mmercial aviation company, 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 analysis by diffraction of polycrystalline materials can determine the full tensor of the elastic strains within them. Point-bypoint maps of elastic strain can thus be obtained in fine-grained engineering alloys, typically using synchrotron X-rays or neutrons. In this paper, a novel approach is presented to calculate the elastic strain energy release rate of a loaded crack from two-dimensional strain maps that are obtained by diffraction. The method is based on a Finite Element approach, which uses diffraction data to obtain the parameters required to calculate the J-integral via the contour integral method. The J integral is robust to uncertainties in the crack tip position and to poor definition of the field in the crack vicinity, and does not rely on theoretical assumptions of the field shape. A validation of the technique is presented using a synthetic dataset from a finite element model. Its experimental application is demonstrated in an analysis of a synchrotron X-ray diffraction strain map for a loaded fatigue crack in a bainitic steel. Abstract The analysis by diffraction of polycrystalline materials can determine the full tensor of the elastic strains within them. Point-bypoint maps of elastic strain can thus be obtained in fine-grained engineering alloys, typically using synchrotron X-rays or neutrons. In this paper, a novel approach is presented to calculate the elastic strain energy release rate of a loaded crack from two-dimensional strain maps that are obtained by diffraction. The method is based on a Finite Element approach, which uses diffraction data to obtain the parameters required to calculate the J-integral via the contour integral method. The J integral is robust to uncertainties in the crack tip position and to poor definition of the field in the crack vicinity, and does not rely on theoretical assumptions of the field shape. A validation of the technique is presented using a synthetic dataset from a finite element model. Its experimental application is demonstrated in an analysis of a synchrotron X-ray diffraction strain map for a loaded fatigue crack in a bainitic steel.
doi:10.1016/j.prostr.2016.06.315 fatcat:zule7pfuzbhkrjc7ihf3tseaqq