Life Assessment of Large Gas Turbine Blades

Abstract

Large gas turbine nickel based superalloys blades are typically manufactured using an investment casting process. In spite of superior processing and quality control, large turbine blades may contain manufacturing induced discontinuities such as porosities, segregation, chemical inhomogeneities, particles, etc in few of the manufactured parts. These manufacturing discontinuities can significantly influence the reliable component life if they are under a load condition where they will form a crack. A typical engineering approach is to treat these discontinuities as a crack from the beginning of the part life. This leads to a conservative life prediction, as crack nucleation and influencing geometrical details of the discontinuities are neglected. This paper presents a framework and path forward for a comprehensive life assessment. It includes computer tomography (CT) analysis, metallographic analysis, local stress analysis, crack formation, as well as state of the art fracture mechanics analysis. For instance, CT and destructive tests reveal details of the geometry of a porous region and thereby enabling the calculation of crack formation life. A subsequent fracture mechanics analysis by engineering tool, FRANC3D can then yield a comprehensive life assessment for comparisons to experimental findings and fleet experience. This approach enables Siemens to diligently ensure that comprehensive life predication assessment has been performed for the components for robust and reliable operation.

Crack nucleation at forging flaws studied by non-local peridynamics simulations

“…Furthermore, the proposed simulation model is not only limited to forging flaws in gas turbine rotor steels, but it can also be used in other engineering applications where crack nucleation from discontinuities is of concern. One example is cast porosities in gas [24] and wind [28] turbine blades. Other promising application examples are additively manufactured and printed engineering components, with their many characteristic discontinuities and inhomogeneities, that are emerging in critical energy and aerospace applications.…”

“…(Left) Strain-life curves (determined by the Coffin Manson Basquin equation [24]) based on experimental data at 20, 350 and 450°C, respectively. (Right) Peridynamics model-calibrated strain-life curves to determine the m 1 and A 1 fatigue parameters.…”

The Modern Single Shaft Gas Turbine Rotor Stress-Strain State Determination Taking into Account the Contact Thermoelasticity Problem

“…2). The whole impellers are approximated by the eight nodes hexagonal finite elements (EL8) [3,15,16]. So, after the FEM approximation the potential energy of the finite element contact deformation can be formed as follows [12,19]:…”

Crystal plasticity modeling of non-Schmid yield behavior: from Ni3Al single crystals to Ni-based superalloys

“…Model considerations for anisotropic creep deformation of Ni-based superalloys may be incorporated in future work. The framework may also be applied for life assessment of gas turbine blades and structures (Narasimhachary et al 2019).…”