Probabilistic Schmid factors and scatter of low cycle fatigue (LCF) life

Gottschalk, Hanno; Schmitz, Sebastian; Seibel, Thomas; Rollmann, Georg; Krause, Rolf; Beck, Tilmann

doi:10.1002/mawe.201400371

Cited by 13 publications

(23 citation statements)

References 16 publications

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“…Its orientation is determining the actual value of the Young's modulus in load direction which generally deviates from the value assumed in the continuous mechanics approach in the local probabilistic model. Gottschalk et al introduced a strain amplitude correction scheme via the concept of Schmid factors for Rene80 data where the orientation of the failing grain was determined by electron backscatter diffraction at every specimen [30]. This leads to a considerable reduction of data scatter.…”

Section: Summarizing Discussionmentioning

confidence: 99%

Combined notch and size effect modeling in a local probabilistic approach for LCF

Mäde

Schmitz

Gottschalk

et al. 2018

Computational Materials Science

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In recent years a local probabilistic model for low cycle fatigue (LCF) based on the statistical size effect has been developed and applied on engineering components. Here, the notch support extension based on the stress gradient effect is described in detail, as well as an FEA-based parameter calibration. An FEA is necessary to simulate non-homogeneous stress fields in non-smooth specimens which exhibit gradients and determine size effects. The hazard density approach and the surface integration over the FEA stress lead to geometryindependent model parameters. Three different materials (superalloys IN-939, Rene80, steel 26NiCrMoV14-5 ) and three different geometry types (smooth, notch, cooling hole specimens) are considered for a more comprehensive validation of the probabilistic LCF model and to demonstrate its wide application range. At the same time, a reduced testing effort is needed compared to deterministic model predictions with notch support.

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Section: Summarizing Discussionmentioning

confidence: 99%

Combined notch and size effect modeling in a local probabilistic approach for LCF

Mäde

Schmitz

Gottschalk

et al. 2018

Computational Materials Science

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“…Plastic deformation of a metallic grain begins if one resolved shear stress within the slip systems of the crystal exceeds a critical value τ CRSS . As the E·m model in [25,31] proposed for coarse grained Ni-base superalloys, the resulting shear stress in the slip systems depends on the grains local Young's moduli and its Schmid factor m. According to [28,30] m is defined as…”

Section: Derivation Of the Schmid Factor Distributionmentioning

confidence: 99%

“…The effects of Schmid factor on the crack initiation and fatigue behavior have been investigated in several studies. Seibel et al [28,29] could show for the coarse grain Ni-base superalloy René80 at 850 • C and low total strain amplitudes, that fatigue cracks initiate on slip bands at grains with high Schmid factors. A plot of the LCF life against the resulting shear stresses in the crack-initiating slip system led to a significant reduction in life scatter compared to a strain Wöhler plot.…”

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confidence: 99%

“…A plot of the LCF life against the resulting shear stresses in the crack-initiating slip system led to a significant reduction in life scatter compared to a strain Wöhler plot. Gottschalk et al [28,30] showed, that there is a correlation between the distribution of the Schmid factor and the lifetime of the Ni-base superalloy René80 tested in high temperature LCF tests. Engel [25,31] could also show coarse grained René80 that, besides the Schmid factor, also the local Young's modulus of the crack initiating grain has a huge influence on the resulting shear stress within the slip systems.…”

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confidence: 99%

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Probabilistic Modeling of Slip System-Based Shear Stresses and Fatigue Behavior of Coarse-Grained Ni-Base Superalloy Considering Local Grain Anisotropy and Grain Orientation

Engel

Mäde

Lion

et al. 2019

Metals

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New probabilistic lifetime approaches for coarse grained Ni-base superalloys supplement current deterministic gas turbine component design philosophies; in order to reduce safety factors and push design limits. The models are based on statistical distributions of parameters, which determine the fatigue behavior under high temperature conditions. In the following paper, Low Cycle Fatigue (LCF) test data of several material batches of polycrystalline Ni-base superalloy René80 with different grain sizes and orientation distribution (random and textured) is presented and evaluated. The textured batch, i.e., with preferential grain orientation, showed higher LCF life. Three approaches to probabilistic crack initiation life modeling are presented. One is based on Weibull distributed crack initiation life while the other two approaches are based on probabilistic Schmid factors. In order to create a realistic Schmid factor distribution, polycrystalline finite element models of the specimens were generated using Voronoi tessellations and the local mechanical behavior investigated in dependence of different grain sizes and statistically distributed grain orientations. All models were first calibrated with test data of the material with random grain orientation and then used to predict the LCF life of the material with preferential grain orientation. By considering the local multiaxiality and resulting inhomogeneous shear stress distributions, as well as grain interaction through polycrystalline Finite Element Analysis (FEA) simulation, the best consistencies between predicted and observed crack initiation lives could be achieved.

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“…This is known as low cycle fatigue (LCF) which, in particular, is a surface driven failure mechanism. The random nature of LCF crack [20]).…”

Section: Introductionmentioning

confidence: 99%

Shape gradients for the failure probability of a mechanic component under cyclic loading: a discrete adjoint approach

Gottschalk

Saadi

2019

Comput Mech

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This work provides a numerical calculation of shape gradients of failure probabilities for mechanical components using a first discretize, then adjoint approach. While deterministic life prediction models for failure mechanisms are not (shape) differentiable, this changes in the case of probabilistic life prediction. The probabilistic, or reliability based, approach thus opens the way for efficient adjoint methods in the design for mechanical integrity. In this work we propose, implement and validate a method for the numerical calculation of the shape gradients of failure probabilities for the failure mechanism low cycle fatigue (LCF), which applies to polycrystalline metal. Numerical examples range from a bended rod to a complex geometry from a turbo charger in 3D.

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Probabilistic Schmid factors and scatter of low cycle fatigue (LCF) life

Cited by 13 publications

References 16 publications

Combined notch and size effect modeling in a local probabilistic approach for LCF

Combined notch and size effect modeling in a local probabilistic approach for LCF

Probabilistic Modeling of Slip System-Based Shear Stresses and Fatigue Behavior of Coarse-Grained Ni-Base Superalloy Considering Local Grain Anisotropy and Grain Orientation

Shape gradients for the failure probability of a mechanic component under cyclic loading: a discrete adjoint approach

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