Anisotropy of material fatigue properties and its effect on durability of structural elements

The generalization of the criterion of multiaxial fatigue failure is proposed for the case of the alloy with the anisotropy of fatigue properties. The second invariant of stress deviator is replaced by the Hill’s function that is usually used to describe anisotropic plasticity of metals. In various studies the dependence of fatigue limit on the axis of loading is investigated for samples with texture at uniaxial fatigue tests. The texture is typically induced during manufacturing semi-finished products (primarily - in rolling). In present study we develop a method for express calculation of stress-strain state (SSS) for the elastic annular disk of variable thickness (disk of the gas turbine engine compressor) for the mode of low-cycle fatigue (flight cycles). Simplified representations are used for dependence of solution on coordinates along the disk thickness (the power series) and in the circumferential direction (the Fourier series). For the radial distribution of stresses and displacements the systems of ordinary differential equations have been derived and solved by the orthogonal sweep method. Proposed criteria of multiaxial fatigue and results are used to calculate the distributions of fatigue durability for typical disk of gas turbine taking into account the centrifugal forces. Location and time to appearance of fatigue failure zones determined accounting the influence of the anisotropy of fatigue properties. The calculations indicated that the significant decrease of the fatigue durability is in the vicinity of the disk rim.