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Repeatability of Tensile Properties in High Pressure Die-Castings of an Al-Mg-Si-Mn Alloy
Hailin Yang,Shouxun Ji,Douglas Watson,Zhongyun Fan 대한금속·재료학회 2015 METALS AND MATERIALS International Vol.21 No.5
High pressure die-castings of an Al-Mg-Si-Mn alloy have been assessed in terms of the repeatability of the mechanical properties including yield strength, ultimate tensile strength and elongation by the normal standard deviations method and by the Weibull statistical model with three parameters. It was found that the round samples had the maximum Weibull modulus, indicating the best repeatability. The machined samples exhibited the second best of Weibull modulus. Among the square samples, the 2 mm and 5 mm thick samples had the lowest and the highest Weibull modulus respectively, indicating that the repeatability for the castings was influenced by the wall thickness. The microstructural uniformity and porosity levels are critical factors in determining the repeatability of the high pressure die-castings. A less segregation in the microstructure could uniform the stress distribution in the die-castings and a less porosity in the casting could reduce the sources for brittle fracture. These improved the repeatability in casting production.
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PM2.5 and PM10 Mass Measurements in California's San Joaquin Valley
Chow, Judith C.,Watson, John G.,Lowenthal, Douglas H.,Chen, L. -W. Antony,Tropp, Richard J.,Park, Kihong,Magliano, Karen A. Taylor Francis 2006 AEROSOL SCIENCE AND TECHNOLOGY Vol.40 No.10
<P> PM2.5 and PM10 mass measurements from different sampling systems and locations within California's San Joaquin Valley (SJV) are compared to determine how well mass concentrations from a unified data set can be used to address issues such as compliance with particulate matter (PM) standards, temporal and spatial variations, and model predictions. Pairwise comparisons were conducted among 20 samplers, including four Federal Reference Method (FRM) units, battery-powered MiniVols, sequential filter samplers, dichotomous samplers, Micro-Orifice Uniform Deposit Impactors (MOUDIs), beta attenuation monitors (BAMs), tapered element oscillating microbalances (TEOMs), and nephelometers. The differences between FRM samplers were less than 10 and 20% for 70 and 92% of the pairwise comparisons, respectively. The TEOM, operating at 50°C in this study, measured less than the other samplers, consistent with other comparisons in nitrate-rich atmospheres. PM2.5 mass measured continuously with the BAM was highly correlated with filter-based PM2.5 although the absolute bias was greater than 20% in 45% of the cases. Light scattering (Bsp) was also highly correlated with filter-based PM2.5 at most sites, with mass scattering efficiencies varying by 10 and 20% for Bsp measured with Radiance Research nephelometers with and without PM2.5 size-selective inlets, respectively. Collocating continuous monitors with filter samplers was shown to be useful for evaluating short-term variability and identifying outliers in the filter-based measurements. Comparability among different PM samplers used in CRPAQS is sufficient to evaluate spatial gradients larger than about 15% when the data are pooled together for spatial and temporal analysis and comparison with models.</P>
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