Mechanical properties of chains with bistable (two-state) units

International audienceGDR MePhy Mécanique et Physique des Sytèmes Complexes (GDR 3588 mixte INSIS/INP) Atelier changements d'échelle, le 5 juin 201

Two temperature model for thermoacoustic sound generation in thick porous thermophones

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Helmholtz and Gibbs ensembles, thermodynamic limit and bistability in polymer lattice models

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Isotensional and isometric force-extension response of chains with bistable units and Ising interactions

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Thermodynamics of small systems with conformational transitions: The case of two-state freely jointed chains with extensible units

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Force-extension response of macromolecular chains with bistable units

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Thermal effects on fracture and brittle-to-ductile transition

The fracture behavior of brittle and ductile materials can be strongly influenced by thermal fluctuations, especially in micro- and nano-devices as well as in rubberlike and biological materials. However, temperature effects, in particular on the brittle-to-ductile transition, still require a deeper theoretical investigation. As a step in this direction we propose a theory, based on equilibrium statistical mechanics, able to describe the temperature dependent brittle fracture and brittle-to-ductile transition in prototypical discrete systems consisting in a lattice with breakable elements. Concerning the brittle behavior, we obtain closed form expressions for the temperature-dependent fracture stress and strain, representing a generalized Griffith criterion, ultimately describing the fracture as a genuine phase transition. With regard to the brittle-to-ductile transition, we obtain a complex critical scenario characterized by a threshold temperature between the two fracture regimes (brittle and ductile), an upper and a lower yield strength, and a critical temperature corresponding to the complete breakdown. To show the effectiveness of the proposed models in describing thermal fracture behaviors at small scales, we successfully compare our theoretical results with molecular dynamics simulations of Si and GaN nanowires.Comment: 27 pages, 20 figure

Vibrotactile sensitivity in active touch: effect of pressing force

An experiment was conducted to study the effects of force produced by active touch on vibrotactile perceptual thresholds. The task consisted in pressing the fingertip against a flat rigid surface that provided either sinusoidal or broadband vibration. Three force levels were considered, ranging from light touch to hard press. Finger contact areas were measured during the experiment, showing positive correlation with the respective applied forces. Significant effects on thresholds were found for vibration type and force level. Moreover, possibly due to the concurrent effect of large (unconstrained) finger contact areas, active pressing forces, and long duration stimuli, the measured perceptual thresholds are considerably lower than what previously reported in the literature