Exponent

About: Exponent is a company organization based out in Menlo Park, California, United States. It is known for research contribution in the topics: Population & Risk assessment. The organization has 1589 authors who have published 2680 publications receiving 88140 citations.

Determination of the toughness of in-service steam turbine disks using small punch testing

Abstract: Knowledge of the material toughness is crucial in assessing the integrity of heavy section steel components. Conventional tests to determine the toughness involve extraction of large blocks of materials and therefore are not practical on in-service components. On the other hand, conservative assumptions regarding toughness without regard to actual data can lead to expensive and premature replacement of the components. Previous EPRI studies have demonstrated the use of a relatively nondestructive technique termed the “small punch test” to estimate the fracture appearance transition temperature (FATT) and fracture toughness (KIc) of high-temperature turbine rotor steels and nuclear reactor pressure vessel steels. This paper summarizes the results of research into the feasibility of extending the small punch test to characterize the toughness of the 3 to 3.5% NiCrMoV (3–3.5NiCrMoV) low alloy steel used for fossil and nuclear power plant low-pressure (LP) steam turbine disks. Results of the present study show that the small punch transition temperature, Tsp, is linearly correlated with FATT, so that measurement of Tsp permits estimation of the standard Charpy FATT through empirical use of the correlation. The statistical confidence prediction uncertainty bands for the correlation were found to be narrow enough to make the small punch- based FATT estimation practical for this alloy. Additionally, independent KIc measurements made by PowerGen, UK, on some of the same test materials were in excellent agreement with measurements made here, indicating that the small punch KIc measurement can be reproducible across laboratories. Limited testing for fracture initiation toughness showed, as has been demonstrated for other materials, that the small punch test-based initiation fracture toughness (KIc) determination was within ±25% of the ASTM standard measurement of KIc, suggesting that the test method can be used for direct determination of fracture initiation toughness.

Thermoplasmonic Ignition of Metal Nanoparticles

Abstract: Explosives, propellants, and pyrotechnics are energetic materials that can store and quickly release tremendous amounts of chemical energy. Aluminum (Al) is a particularly important fuel in many applications because of its high energy density, which can be released in a highly exothermic oxidation process. The diffusive oxidation mechanism (DOM) and melt-dispersion mechanism (MDM) explain the ways powders of Al nanoparticles (NPs) can burn, but little is known about the possible use of plasmonic resonances in NPs to manipulate photoignition. This is complicated by the inhomogeneous nature of powders and very fast heating and burning rates. Here, we generate Al NPs with well-defined sizes, shapes, and spacings by electron beam lithography and demonstrate that their plasmonic resonances can be exploited to heat and ignite them with a laser. By combining simulations with thermal-emission, electron-, and optical-microscopy studies, we reveal how an improved control over NP ignition can be attained.

Fur-rubbing behavior of capuchin monkeys.

Abstract: T he world’s shortest poem, “Fleas,” has only three words: Adam/Had ’em. The dermatologic interpretation is that ectoparasites have annoyed man ever since, well, ever since Adam. Or maybe before that, because evolutionary biologists theorize that the ancestors of Homo sapiens and the ancestors of anthropophagous ectoparasites coevolved over eons.1 Humans have several ways to prevent and treat their ectoparasite infestations. Most other animals are limited to scratching or biting themselves or rubbing against fixed objects to obtain relief from annoying arthropods. Nonhuman primates, on the other hand, have more sophisticated responses. In social grooming, members of a primate troop pair off and pick arthropods and nits from each other in a highly structured manner. The white-faced or capuchin monkey (Cebus capuchinus) has another specialized behavior known as fur rubbing. Dr Mary Baker, an anthropologist from the University of California at Riverside, spent years observing this behavior in wild capuchins. The capuchins break up plants, both manually and orally, and rub the material over their bodies.2 We believe that the capuchins use these plants to rid themselves of lice, mites, and ticks. In 1998, R. T. and M. D. traveled by plane, bus, boat, and truck to the rainforests of Costa Rica to study ectoparasitism in capuchins. Our research site, El Refugio de Vida Silvestre Curu, is in the dense lowland forests along Costa Rica’s Pacific coast. The Refugio, a 3706-acre haven of biodiversity, is home to more than 400 species of vertebrates and 400 species of vascular plants. The family who owns the Refugio welcomes the use of their land for research, education, and ecotourism.3 The owners permit scientists from Cornell University to conduct field studies and to collect plants for phytochemical analysis and biologic evaluation at Cornell. We observed the monkeys in their natural habitat (Fig 1) and collected plant specimens to better unFrom Exponent, New York, the Department of Biology, Hollins University, Roanoke, the Department of Anthropology, Pomona College, Claremont, and the Department of Plant Biology, Cornell University, Ithaca. Funding sources: Cornell University and The Explorers Club of New York. Presented in part at a poster session at The International Conference on Ethnomedicine and Drug Discovery, Silver Spring, Md, Nov 3-5, 1999. Reprint requests: Maria DeJoseph, MS, Exponent, 420 Lexington Ave, Suite 408, New York, NY 10170.