@article {1581, title = {Microscale characterization of damage accumulation in CMCs}, journal = {Journal of the European Ceramic Society}, year = {2020}, abstract = {

The developing roles of damage mechanisms in the failure response of SiC/SiC minicomposites was investigated by the characterization of microscale damage accumulation with respect to microstructure. A multi-modal approach combining spatially resolved acoustic emission (AE) with tensile testing in-SEM (scanning electron microscope) was used to simultaneously examine surface (observed in-SEM) and bulk damage (monitored via AE). Strong agreement was shown between the evolving crack density estimated by AE and in-SEM measurements. The following were observed: (i) in-plane matrix content and distribution impacted crack growth; (ii) spatially-distributed matrix cracks generated varying stress-dependent AE; and (iii) certain individual cracks became more probable failure locations due to unique combinations of damage mechanisms that drove their growth. This approach enabled characterizing potential failure determinants and suggests that early damage behavior is related to certain microstructural features (e.g. surface flaws), while subsequent damage behavior is coupled to interactions of local mechanisms evolving with stress.

}, keywords = {Acoustic emission, Ceramic matrix composite, Cracking, Damage initiation, Silicon carbide}, issn = {1873619X}, doi = {10.1016/j.jeurceramsoc.2020.05.077}, url = {https://doi.org/10.1016/j.jeurceramsoc.2020.05.077}, author = {Swaminathan, B. and McCarthy, N. R. and Almansour, A. S. and Sevener, K. and Pollock, T. M. and Kiser, J. D. and Daly, S.} } @article {1436, title = {Measurements of plastic localization by heaviside-digital image correlation}, journal = {Acta Materialia}, volume = {157}, year = {2018}, pages = {307{\textendash}325}, abstract = {

In polycrystalline metallic materials, quantitative and statistical assessment of the plasticity in relation to the microstructure is necessary to understand the deformation processes during mechanical loading. Plastic deformation often localizes into physical slip bands at the sub-grain scale. Detrimental microstructural configurations that result in the formation and evolution of slip bands during loading require advanced strain mapping techniques for the identification of these atomically sharp discontinuities. A new discontinuity-tolerant DIC method, Heaviside-DIC, has been developed to account for discontinuities in the displacement field. Displacement fields have been measured at the scale of the physical slip bands over large areas in nickel-based superalloys by high resolution scanning electron microscopy digital image correlation (SEM DIC). However, conventional DIC methods cannot quantitatively measure plastic localization in the presence of discontinuous kinematic fields such as those produced by slip bands. The Heaviside-DIC technique can autonomously detect discontinuities, providing information about their location, inclination, and identify slip systems (in combination with orientation mapping). Using Heaviside-DIC, discontinuities are physically evaluated as sharp shear-localization events, allowing for the quantitative measure of strain amplitude nearby the discontinuities. Measurements using the new Heaviside-DIC technique are compared to conventional DIC methods for identical materials and imaging conditions.

}, keywords = {Discontinuities measurements, High resolution digital image correlation, Ren{\'e} 88DT polycrystalline superalloy, Scanning electron microscopy, Slip band offset, Slip band shearing, Slip system identification, Strain localization}, issn = {13596454}, doi = {10.1016/j.actamat.2018.07.013}, url = {https://doi.org/10.1016/j.actamat.2018.07.013}, author = {Bourdin, F. and Stinville, J. C. and Echlin, M. P. and Callahan, P. G. and Lenthe, W. C. and Torbet, C. J. and Texier, D. and Bridier, F. and Cormier, J. and Villechaise, P. and Pollock, T. M. and Valle, V.} } @article {1456, title = {Microstructure and property based statistically equivalent RVEs for intragranular γ-γ{\textquoteright} microstructures of Ni-based superalloys}, journal = {Acta Materialia}, volume = {157}, year = {2018}, pages = {245{\textendash}258}, abstract = {

This paper develops statistically equivalent RVEs or SERVEs for intragranular microstructures of Ni-based superalloys, characterized by \γ-\γ\&$\#$39; phase distribution. The SERVE represents an optimal computational domain to be used for micromechanical simulations for effective properties or response variables in the microstructure. The SERVE is further classified as a microstructure-based SERVE or M-SERVE or property-based SERVE or P-SERVE, depending on whether the statistics of morphological characteristics or convergence of chosen material properties are its determinants. Starting from FIB-SEM data for the superalloy Ren\é 88DT, the paper systematically develops a host of algorithms for generating validated statistically equivalent virtual microstructures, from which the M-SERVE is estimated from convergence of selected morphological and spatial distributions. Subsequently the P-SERVEs are established for global properties like yield strength and hardening rate, and local variables including dislocation density and the maximum resolved shear stress. Spatially-averaged quantities are found to converge quicker than the local distributions for both M-SERVE and P-SERVE.

}, keywords = {M-SERVE, Ni-based superalloys, P-SERVE, SEVM, Two-point correlation function, γ-γ{\textquoteright} distribution}, issn = {13596454}, doi = {10.1016/j.actamat.2018.07.034}, url = {https://doi.org/10.1016/j.actamat.2018.07.034}, author = {Pinz, M. and Weber, G. and Lenthe, W. C. and Uchic, M. D. and Pollock, T. M. and Ghosh, S.} } @article {1221, title = {Measurement of Strain Localization Resulting from Monotonic and Cyclic Loading at 650 oC in Nickel Base Superalloys}, journal = {Experimental Mechanics}, volume = {57}, year = {2017}, pages = {1289{\textendash}1309}, doi = {10.1007/s11340-017-0286-y}, author = {Stinville, J. C. and Echlin, M. P. and Callahan, P. G. and Miller, V. M. and Texier, D. and Bridier, F. and Bocher, P. and Pollock, T. M.} }