A Crystal Plasticity Finite Element (CPFE) framework is proposed for modeling the non-Schmid yield behavior of L12 type Ni3Al crystals and Ni-based superalloys. This framework relies on the estimation of the non-Schmid model parameters directly from the orientation- and temperature-dependent experimental yield stress data. The inelastic deformation model for Ni3Al crystals is extended to the precipitate phase of Ni-based superalloys in a homogenized dislocation density based crystal plasticity framework. The framework is used to simulate the orientation- and temperature-dependent yield of Ni3Al crystals and single crystal Ni-based superalloy, CMSX-4, in the temperature range 260-1304 K. Model predictions of the yield stress are in general agreement with experiments. Model predictions are also made regarding the tension-compression asymmetry and the dominant slip mechanism at yield over the standard stereographic triangle at various temperatures for both these materials. These predictions provide valuable insights regarding the underlying (orientation- and temperature-dependent) slip mechanisms at yield. In this regard, the non-Schmid model may also serve as a standalone analytical model for predicting the yield stress, the tension-compression asymmetry and the underlying slip mechanism at yield as a function of orientation and temperature.

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

Crack nucleation from non-metallic inclusions in aluminum alloys described by peridynamics simulations

Abstract Creep crack growth experiments were performed at 750°C, 850°C, and 950°C on nominally 3 and 12.7 mm thick compact type specimens of alloy 247LC‐DS, a Ni‐base superalloy used for hot‐section gas turbine blades. The primary crack plane was transverse to the solidification direction. The crack path–microstructure interaction was characterized. Crack growth occurred in a creep‐ductile manner and data analyses utilized time‐dependent fracture mechanics. No measurable crack growth occurred at 750°C. Cracks grew by formation, growth, and coalescence of cavities on interdendritic carbides in both the primary crack plane and normal to said plane at 850°C and 950°C. The variability in the crack growth rate was higher in thicker specimens, but the mean creep crack growth rate versus C t relationship in 247LC‐DS was neither sensitive to test temperature ≥850°C nor specimen thickness. Quantitative relationships between da/dt and C t were derived for mean, upper, and lower bound creep crack growth rate trends. 

Creep crack growth in alloy 247LC‐DS

The paper outlines a finite elements refined mathematical model of the stress-strain state of single shaft gas turbine engine that can be used in ground or floating power plants. The mathematical model is taken into consideration the contact thermoelasticity problem in the joint area of disk and blades. On the base of the developed mathematical model the fields of turbine rotor dynamic stresses and displacement have been found too. To make the clear decision about the developed mathematical model adequacy mostly loaded impeller dynamic stresses field has been found and verified by comparison with the calculated results without contact and experimental data. The turbine rotor displacements and dynamic stresses have been found for different forced vibration modes. The obtained results along with the previous studies of this rotor fluid flow and thermal state could be used in further studies of the turbine rotor creep and fatigue strength and blades crack researches.

pdf/the-modern-single-shaft-gas-turbine-rotor-stress-strain-2c1q5ivu4w.pdf

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


 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.

Life Assessment of Large Gas Turbine Blades

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Life Assessment of Large Gas Turbine Blades