Abstract
This work provides an experimental and computational analysis of low cycle fatigue of a tantalum polycrystalline aggregate. The experimental results include strain field and lattice rotation field measurements at the free surface of a tension–compression test sample after 100, 1000, 2000, and 3000 cycles at ±0.2% overall strain. They reveal the development of strong heterogeneites of strain, plastic slip activity, and surface roughness during cycling. Intergranular and transgranular cracks are observed after 5000 cycles. The Crystal Plasticity Finite Element simulation recording more than 1000 cycles confirms the large strain dispersion at the free surface and shows evidence of strong local ratcheting phenomena occurring in particular at some grain boundaries. The amount of ratcheting plastic strain at each cycle is used as the main ingredient of a new local fatigue crack initiation criterion.
Highlights
Polycrystalline tantalum, a refractory material used in several industrial applications such as nuclear, biomedical, and chemical engineering, has been the subject of intensive research dealing with the understanding of plastic deformation modes, mainly at large strain and strain rates [1,2,3]
They include Electron Back-Scatter Diffraction (EBSD) analysis of crystal lattice orientation and its evolution during deformation, Digital Image Correlation (DIC) analysis for the determination of strain fields [5], as well as Crystal Plasticity Finite Element simulations (CPFEM) at the continuum level relying on appropriate constitutive equations [6], and molecular dynamics simulations [7]
The results presented in this work correspond to the simulation of more than 1000 cycles on the previously described polycrystalline aggregate
Summary
Polycrystalline tantalum, a refractory material used in several industrial applications such as nuclear, biomedical, and chemical engineering, has been the subject of intensive research dealing with the understanding of plastic deformation modes, mainly at large strain and strain rates [1,2,3]. Modern experimental and computational techniques have been applied to body centered cubic (BCC) metals at the grain level [4] They include Electron Back-Scatter Diffraction (EBSD) analysis of crystal lattice orientation and its evolution during deformation, Digital Image Correlation (DIC) analysis for the determination of strain fields [5], as well as Crystal Plasticity Finite Element simulations (CPFEM) at the continuum level relying on appropriate constitutive equations [6], and molecular dynamics simulations [7]. These techniques have been applied to tantalum polycrystals and oligocrystals in [8,9].
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