210 research outputs found
Back stress in dislocation creep. Part 1: Basic concepts and measuring techniques
A theory is proposed whereby the plastic deformation of metal materials is determined by the difference between the applied stress and the back stress which characterizes the resistance of the material to plastic deformation. The back stress is usually equivalent to the internal stress or the friction stress and depends on the magnitude of the applied stress and temperature. The concept of back stress is applied to the case of the dislocation creep of precipitation-hardened or dispersion-strengthened metal materials. An additivity rule is formulated which can be useful in interpreting the creep behavior of such materials
Analysis of the creep response of a fine-grained magnesium-rare earths alloy produced by rapid solidification
The creep response of a experimental Mg-Zn-Ca-Ce-La alloy produced by rapid solidification was investigated at temperatures ranging from 498 to 548K, under stresses from 7 to 50MPa. The creep curves exhibited a short primary region, during which the strain rate decreases, followed by a short minimum creep rate range, and by a very long tertiary stage. The analysis of the creep rate dependence on applied stress at different strain suggested that the creep mechanisms was cross slip on non-basal plane, or alternatively glide of dislocation on pyramidal slip system controlled by nucleation of kink motion
Radius and chirality dependent conformation of polymer molecule at nanotube interface
Temperature dependent conformations of linear polymer molecules adsorbed at
carbon nanotube (CNT) interfaces are investigated through molecule dynamics
simulations. Model polyethylene (PE) molecules are shown to have selective
conformations on CNT surface, controlled by atomic structures of CNT lattice
and geometric coiling energy. PE molecules form entropy driven assembly
domains, and their preferred wrapping angles around large radius CNT (40, 40)
reflect the molecule configurations with energy minimums on a graphite plane.
While PE molecules prefer wrapping on small radius armchair CNT (5, 5)
predominantly at low temperatures, their configurations are shifted to larger
wrapping angle ones on a similar radius zigzag CNT (10, 0). A nematic
transformation around 280 K is identified through Landau-deGennes theory, with
molecule aligning along tube axis in extended conformationsComment: 19 pages, 7 figure2, submitted to journa
Spectral numerical schemes for time-dependent convection with viscosity dependent on temperature
This article proposes spectral numerical methods to solve the time evolution
of convection problems with viscosity strongly depending on temperature at
infinite Prandtl number. Although we verify the proposed techniques just for
viscosities that depend exponentially on temperature, the methods are
extensible to other dependence laws. The set-up is a 2D domain with periodic
boundary conditions along the horizontal coordinate. This introduces a symmetry
in the problem, the O(2) symmetry, which is particularly well described by
spectral methods and motivates the use of these methods in this context. We
examine the scope of our techniques by exploring transitions from stationary
regimes towards time dependent regimes. At a given aspect ratio stable
stationary solutions become unstable through a Hopf bifurcation, after which
the time-dependent regime is solved by the spectral techniques proposed in this
article.Comment: 17 pages, 7 figure
Propriedades mecânicas, tribológicas e térmicas de nanocompósitos de PLLA com nanotubos de carbono de paredes múltiplas
Mesoscale structures in the transition zone: Dynamical consequences of boundary layer activities
Can We Optimize Arc Discharge and Laser Ablation for Well-Controlled Carbon Nanotube Synthesis?
A multi-country test of brief reappraisal interventions on emotions during the COVID-19 pandemic
The COVID-19 pandemic has increased negative emotions and decreased positive emotions globally. Left unchecked, these emotional changes might have a wide array of adverse impacts. To reduce negative emotions and increase positive emotions, we tested the effectiveness of reappraisal, an emotion-regulation strategy that modifies how one thinks about a situation. Participants from 87 countries and regions (n = 21,644) were randomly assigned to one of two brief reappraisal interventions (reconstrual or repurposing) or one of two control conditions (active or passive). Results revealed that both reappraisal interventions (vesus both control conditions) consistently reduced negative emotions and increased positive emotions across different measures. Reconstrual and repurposing interventions had similar effects. Importantly, planned exploratory analyses indicated that reappraisal interventions did not reduce intentions to practice preventive health behaviours. The findings demonstrate the viability of creating scalable, low-cost interventions for use around the world
Creep behaviour at high stresses of a Mg-Zn-Ca-Ce-La alloy procesed by rapid solidification
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