Albion College

About: Albion College is a education organization based out in Albion, Michigan, United States. It is known for research contribution in the topics: Population & Higher education. The organization has 485 authors who have published 754 publications receiving 20907 citations.

The effect of grain boundary normal on predicting microcrack nucleation using fracture initiation parameters in duplex TiAl

Abstract: In a prior study of a duplex Ti–48Al–2Cr–2Nb, Simkin et al. [B.A. Simkin, M.A. Crimp, T.R. Bieler, Scripta Mater. 49 (2003) 149], 11 cracked and 11 intact boundaries between γ grains were analyzed to determine why some boundaries that were similarly stressed cracked, and others did not. This led to a geometrically based fracture initiation parameter that considered the tensile stress axis and the deformation systems in both grains. In order to further examine the physical basis of this fracture initiation parameter, we have measured the grain boundary orientation of the previously studied boundaries. In contrast to the expectation that incorporation of the grain boundary orientation into this parameter would improve the ability to discriminate between cracked and intact boundaries, the orientation of the grain boundary normal was found to be statistically less significant than the orientation of the Burgers vectors of the most highly stressed twinning systems, quantified by | b ˆ tw ⋅ t ˆ | , where t ˆ describes the tensile axis direction. Grain boundary microcracking was found to be most likely when b ˆ tw was in the range of 30–50° from the tensile axis. Combining the Schmid factor with | b ˆ tw ⋅ t ˆ | and the effect of ordinary dislocation slip accommodation provides a simple and effective predictor of the propensity for microcrack nucleation.

Apollo 17 regolith, 71501,262: A record of impact events and mare volcanism in lunar glasses

Abstract: Thirteen glasses from Apollo 17 regolith 71501,262 have been chemically analyzed by electron microprobe and isotopically dated with the 40Ar/39Ar dating method We report here the first isotopic age obtained for the Apollo 17 very low titanium (VLT) volcanic glasses, 3630 ± 40 Ma Twelve impact glasses that span a wide compositional range have been found to record ages ranging from 102 ± 20 Ma to 3740 ± 50 Ma The compositions of these impact glasses show that some have been produced by impact events within the Apollo 17 region, whereas others appear to be exotic to the landing site As the data sets that include compositions and ages of lunar impact glasses increase, the impact history in the Earth-Moon system will become better constrained