The effects of particle size, volume fraction and matrix strength on the stress-controlled axial fatigue behavior and the probability of particle fracture were evaluated for 2124 aluminum alloy reinforced with SiC particles. Average particle sizes of 2, 5, 9 and 20/~m and volume fractions of 0.10, 0.20 and 0.35 were examined for four different microstructural conditions. Tensile and yield strengths and fatigue life were substantially higher in the reinforced alloys. Strength and fatigue life increased as reinforcement particle size decreased and volume fraction loading increased. The frequency of particle fracture during crack propagation was found to be dependent on matrix strength, particle size and volume fraction and on maximum crack tip stress intensity. Particle fracture can be rationalized, phenomenologically, by the application of modified process zone models, originally derived for static fracture processes, and weakest link statistics which account for the dependence of matrix yield strength and flow behavior and particle strength on the probability of particle fracture during monotonic fracture and fatigue crack propagation.

The localization of mouse placental lactogen (mPL) in the mouse placenta has been examined with the avidinbiotin-peroxidase complex (ABC) technique. Staining was observed to occur in the basal zone of placentae from days 10, 12, 15, and 18 of gestation. Within the basal zone, the most prominent staining was localized to the cytoplasm of

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