@article {1796,
	title = {Grain-Scale Stress States in Microtextured Ti64: Implications for Dwell Fatigue},
	journal = {Jom},
	volume = {74},
	year = {2022},
	pages = {3709{\textendash}3719},
	abstract = {<p>
	The room-temperature fatigue life of titanium alloys with a significant alpha phase fraction is substantially reduced when the peak stress is sustained for a few minutes on each stress cycle. Furthermore, these alloys often form microtextured regions during forging which are known to increase the dwell debit; however, the mechanisms for this reduction are still not well understood. In this research, an experimentally collected 3D microstructure of equiaxed Ti-6Al-4V containing microtextured regions is used as input for linear elastic finite element analysis of grain-level stress states relevant to dwell fatigue. The directional strength to stiffness ratio and a metric related to local plane strain are evaluated around the microtextured regions. Strength to stiffness ratios indicate that misoriented grains within hard microtextured regions will begin to yield at macroscopic stress levels below the yield strength, and, under certain loading conditions, they will yield at lower macroscopic stresses than any other location in the microstructure. Under uniaxial tension, boundaries between hard and soft microtextured regions experience some degree of plane strain loading, which may be linked to enhanced load shedding in these areas during dwell fatigue.
</p>
},
	isbn = {1183702205},
	issn = {15431851},
	doi = {10.1007/s11837-022-05423-9},
	url = {https://doi.org/10.1007/s11837-022-05423-9},
	author = {Wendorf, Joe and Dawson, Paul R. and Pollock, Tresa M.}
}
@article {1451,
	title = {Grain size effects on NiTi shape memory alloy fatigue crack growth},
	journal = {Journal of Materials Research},
	volume = {33},
	year = {2018},
	pages = {91{\textendash}107},
	abstract = {<p>
	Fatigue cracking in polycrystalline NiTi was investigated using a multiscale experimental framework for average grain sizes (GS) from 10 to 1500 nm for the first time. Macroscopic fatigue crack growth rates, measured by optical digital image correlation, were connected to microscopic crack opening and closing displacements, measured by scanning electron microscope DIC (SEM-DIC) using a high-precision external SEM scan controller. Among all grain sizes, the 1500 nm GS sample exhibited the slowest crack growth rate at the macroscale, and the largest crack opening level (stress intensity at first crack opening) and minimum crack opening displacements at the microscale. Smaller GS samples (10, 18, 42, and 80 nm) exhibited nonmonotonic trends in their fatigue performance, yet the correlation was strong between macroscale and microscale behaviors for each GS. The samples that exhibited the fastest crack growth rates (42 and 80 nm GS) showed a small crack opening level and the largest crack opening displacements. The irregular trends in fatigue performance across the nanocrystalline GS samples were consistent with nonmonotonic values in the elastic modulus reported previously, both of which may be related to the presence of residual martensite only evident in the small GS samples (10 and 18 nm).
</p>
},
	keywords = {fatigue, nanostructure, scanning electron microscopy (SEM)},
	issn = {20445326},
	doi = {10.1557/jmr.2017.395},
	author = {Lepage, William S. and Ahadi, Aslan and Lenthe, William C. and Sun, Qing Ping and Pollock, Tresa M. and Shaw, John A. and Daly, Samantha H.}
}
