Grain Level Dwell Fatigue Crack Nucleation Model for Ti Alloys Using Crystal Plasticity Finite Element Analysis

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Kedar Kirane ◽  
Somnath Ghosh ◽  
Mike Groeber ◽  
Amit Bhattacharjee
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Crack Initiation ◽  
Crystal Plasticity ◽  
Field Experiments ◽  
System Level ◽  
Fe Model ◽  
Fatigue Crack Nucleation ◽  
Crystal Plasticity Finite Element ◽  
Dwell Fatigue

A microstructure sensitive criterion for dwell fatigue crack initiation in polycrystalline alloy Ti-6242 is proposed in this paper. Local stress peaks due to load shedding from time dependent plastic deformation fields in neighboring grains are held responsible for crack initiation in dwell fatigue. An accurately calibrated and experimentally validated crystal plasticity finite element (FE) model is employed for predicting slip system level stresses and strains. Vital microstructural features related to the grain morphology and crystallographic orientations are accounted for in the FE model by construction of microstructures that are statistically equivalent to those observed in orientation imaging microscopy scans. The output of the finite element method model is used to evaluate the crack initiation condition in the postprocessing stage. The functional form of the criterion is motivated from the similarities in the stress fields and crack evolution criteria ahead of a crack tip and dislocation pileup. The criterion is calibrated and validated by using experimental data obtained from ultrasonic crack monitoring techniques. It is then used to predict the variation in dwell fatigue lifetime for critical microstructural conditions. The studies are extended to field experiments on β forged Ti-6242. Macroscopic aspects of loading are explored for their effect on dwell fatigue life of Ti-6242.

A high-fidelity crystal-plasticity finite element methodology for low-cycle fatigue using automatic electron backscatter diffraction scan conversion: Application to hot-rolled cobalt–chromium alloy

2021 ◽  
pp. 146442072110108
Author(s):  
Yuhui Tu ◽  
Seán B Leen ◽  
Noel M Harrison
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Crack Initiation ◽  
Crystal Plasticity ◽  
Electron Backscatter Diffraction ◽  
Voronoi Tessellation ◽  
Fatigue Crack Initiation ◽  
Crystal Plasticity Finite Element ◽  
Electron Backscatter ◽  
Backscatter Diffraction

The common approach to crystal-plasticity finite element modeling for load-bearing prediction of metallic structures involves the simulation of simplified grain morphology and substructure detail. This paper details a methodology for predicting the structure–property effect of as-manufactured microstructure, including true grain morphology and orientation, on cyclic plasticity, and fatigue crack initiation in biomedical-grade CoCr alloy. The methodology generates high-fidelity crystal-plasticity finite element models, by directly converting measured electron backscatter diffraction metal microstructure grain maps into finite element microstructural models, and thus captures essential grain definition for improved microstructure–property analyses. This electron backscatter diffraction-based method for crystal-plasticity finite element model generation is shown to give approximately 10% improved agreement for fatigue life prediction, compared with the more commonly used Voronoi tessellation method. However, the added microstructural detail available in electron backscatter diffraction–crystal-plasticity finite element did not significantly alter the bulk stress–strain response prediction, compared to Voronoi tessellation–crystal-plasticity finite element. The new electron backscatter diffraction-based method within a strain-gradient crystal-plasticity finite element model is also applied to predict measured grain size effects for cyclic plasticity and fatigue crack initiation, and shows the concentration of geometrically necessary dislocations around true grain boundaries, with smaller grain samples exhibiting higher overall geometrically necessary dislocations concentrations. In addition, minimum model sizes for Voronoi tessellation–crystal-plasticity finite element and electron backscatter diffraction–crystal-plasticity finite element models are proposed for cyclic hysteresis and fatigue crack initiation prediction.

Simulation of Fatigue Crack Initiation in Heat Affected Zone Microstructure Using Crystal-Plasticity Finite Element Method

2017 ◽  
Author(s):  
Takashi Hiraide ◽  
Satoshi Igi ◽  
Tetsuya Tagawa ◽  
Rinsei Ikeda ◽  
Seiichiro Tsutsumi
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Fatigue Crack ◽  
Crack Initiation ◽  
Crystal Plasticity ◽  
Heat Affected Zone ◽  
Fatigue Crack Initiation ◽  
Crystal Plasticity Finite Element ◽  
Microstructural Effects ◽  
Inhomogeneous Microstructure

It is well known that fatigue fracture of welded joints can depend on many factors such as residual stress, stress concentration and an inhomogeneous microstructure in the HAZ (Heat Affected Zone). Some solutions to improve fatigue properties, for example, hammer peening (1), have been developed to mitigate effects related to stress. Improvement from mechanical view point is not only applied, but optimized microstructure design of the base metal and HAZ should be also considered. However, microstructural effects on fatigue crack initiation behavior have not been fully understood because systematic experimental evaluation of them takes much efforts with difficulty. An analytical method is a useful idea to specify the optimum microstructure against fatigue crack initiation before experimental examinations. CP-FEM (Crystal-Plasticity Finite Element Method) is expected to describe fatigue crack initiation behavior, because it can express strain localizations caused by an inhomogeneous microstructure. In the present study, a simulation model using CP-FEM is developed to describe strain localizations under cyclic loading. Microstructural effects on plastic strain localization and accumulation were investigated by changing microstructural factors.

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