Rheology and ultrasonic properties of Pt57.5Ni5.3Cu14.7P22.5 liquid

The equilibrium and nonequilibrium viscosity and isoconfigurational shear modulus of Pt57.5Ni5.3Cu14.7P22.5 supercooled liquid are evaluated using continuous–strain-rate compression experiments and ultrasonic measurements. By means of a thermodynamically-consistent cooperative shear model, variations in viscosity with both temperature and strain rate are uniquely correlated to the variations in isoconfigurational shear modulus, which leads to an accurate prediction of the liquid fragility and to a good description of the liquid strain-rate sensitivity

Anelastic to Plastic Transition in Metallic Glass-Forming Liquids

The configurational properties associated with the transition from anelasticity to plasticity in a transiently deforming metallic glass-forming liquid are studied. The data reveal that the underlying transition kinetics for flow can be separated into reversible and irreversible configurational hopping across the liquid energy landscape, identified with beta and alpha relaxation processes, respectively. A critical stress characterizing the transition is recognized as an effective Eshelby “backstress,” revealing a link between the apparent anelasticity and the “confinement stress” of the elastic matrix surrounding the plastic core of a shear transformation zone

Deformation of glass forming metallic liquids: Configurational changes and their relation to elastic softening

The change in the configurational enthalpy of metallic glass forming liquids induced by mechanical deformation and its effect on elastic softening is assessed. The acoustically measured shear modulus is found to decrease with increasing configurational enthalpy by a dependence similar to one obtained by softening via thermal annealing. This establishes that elastic softening is governed by a unique functional relationship between shear modulus and configurational enthalpy

Stochastic Metallic-Glass Cellular Structures Exhibiting Benchmark Strength

By identifying the key characteristic “structural scales” that dictate the resistance of a porous metallic glass against buckling and fracture, stochastic highly porous metallic-glass structures are designed capable of yielding plastically and inheriting the high plastic yield strength of the amorphous metal. The strengths attainable by the present foams appear to equal or exceed those by highly engineered metal foams such as Ti-6Al-4V or ferrous-metal foams at comparable levels of porosity, placing the present metallic-glass foams among the strongest foams known to date

Cooperative Shear Model for the Rheology of Glass-Forming Metallic Liquids

A rheological law based on the concept of cooperatively sheared flow zones is presented, in which the effective thermodynamic state variable controlling flow is identified to be the isoconfigurational shear modulus of the liquid. The law captures Newtonian as well as non-Newtonian viscosity data for glass-forming metallic liquids over a broad range of fragility. Acoustic measurements on specimens deformed at a constant strain rate correlate well with the measured steady-state viscosities, hence verifying that viscosity has a unique functional relationship with the isoconfigurational shear modulus

Detection of Large Grains in the Coma of Comet C/2001 A2 (LINEAR) from Arecibo Radar Observations

Arecibo S-band (lambda=13cm) radar observations of Comet C/2001 A2 (LINEAR) on 2001 July 7-9 showed a strong echo from large coma grains. This echo was significantly depolarized. This is the first firm detection of depolarization in a grain-coma radar echo and indicates that the largest grains are at least lambda / 2 or 2 cm in radius. The grains are moving at tens of m/s with respect to the nucleus. The non-detection of the nucleus places an upper limit of 3 km on its diameter. The broad, asymmetric echo power spectrum suggests a fan of grains that have a steep (differential number ~ a^-4) size distribution at cm-scales, though the observed fragmentation of this comet complicates that picture.Comment: 20 pages, 3 tables, 5 figures Submitted to Icaru

Bostonia: The Boston University Alumni Magazine. Volume 20

Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs