Heterogeneous deformation affects material performanceMaterials World Network:

Thomas R. Bieler, Michigan State University, DMR 0710570

Measured Shear (AFM) Simulated Shear (CPFEM)

Predicting or designing material performance depends on how effectively a material model can predict heterogeneous deformation. To evaluate how well a crystal plasticity finite element (CPFE) model performs, the amount of shear on prism, basal, twinning and pyramidal <c+a> systems in different grains of commercial purity titanium was quantitatively measured using Atomic Force Microscopy and Orientation Imaging Microscopy, which we directly compare with our CPFE simulations. The magnitude of strain is correctly modeled in grains in the center of the patch but the spatial distribution of strain within grains is not accurate, due to a lack of information about grains beneath the surface, effect of slip planarity (non-local effects), and grain boundary properties.

Correct Modeling of Heterogeneous Strain will Enable Prediction of Damage Nucleation Sites

Materials World Network: Thomas R. Bieler, Michigan State University, DMR 0710570

The PI organized an International Symposium (to be repeated in 2011) on Deformation and Transitions at grain boundaries, held at MS&T 2009, which brought together researchers (75 talks) from 12 countries on the leading edge of modeling and characterizing grain boundary phenomena, with a special issue in Metall. Mater. Trans. A with 16 papers.

Intact Boundary Fractured Boundary

A scalar fracture initiation parameter (fip) evaluated in the grain boundary plane is related to the probability for grain boundary fracture. The fip evolves during deformation based upon shear on slip systems and stress tensor evolution from CPFE model based on experiment, with higher values in a boundary that fractured (D.E. Mason, Albion College, consultant)

GB damage at strain 1.5%

T1

T1

T1

T1

T1

GB

GB

T2T1

T1

Heterogeneous strain in titanium is accentuated at grain boundaries facilitating damage nucleation such as this microcrack observed after1.5% strain, where many mechanical twins (T1, T2) interacted with a grain boundary (GB).

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