Papers by Keyword: Aging Kinetics

Abstract: on the analysis of the ageing kinetics model, ageing kinetics equation has been established on the basis of complex modulus. Rheological properties test have been carried out on SBS modified asphalt and base asphalt. The results demonstrate that when asphalt material in ageing process, the hypothesis that complex modulus is inversely proportional to the concentration of reactant assumptions of ageing reaction is established, on the basis of which, ageing kinetics constant has been obtained. Ageing kinetics equation has been validated by using measured data, it shows that, SBS modified asphalt owns higher reaction activation energy, a good anti-ageing property as well, that the measured data can keep accordance with calculated data, which demonstrates ageing kinetics equation is established reasonably on the basis of complex modulus. The equation can well describe rheological state changes of asphalt in ageing process.

Abstract: In order to indicate the aging process and evaluate the aging resistance of warm mix asphalt, thin film oven tests of original asphalts and warm mix asphalts were conducted, and the softening points of different asphalts in aging process were compared. Then, using softening point as a parameter, the aging kinetics model was established and the kinetics parameters were also calculated to reflect the aging performance of different asphalts. It is indicated that warm mix asphalt has larger activation energies and lower reaction rate constant than those of original asphalt, and the aging performance of warm mix asphalt after are better. The aging behavior of warm mix asphalt could be well evaluated by the aging kinetics model.

Abstract: Arcelor produces « Bake-Hardening » steels for automotive outer panels, which present the advantages of a remarkable drawability combined with a significant hardening after stamping and paint baking by the car maker. This hardening enables to increase the dent resistance of those automotive parts. In order to give easy design criterion and support the development for new “bake-hardening” steels, a physically-based model for Bake-Hardening steels has been developed. It is suitable to predict: -the physical phenomenon of strain ageing based on Cottrell atmospheres formation. A detailed description of the strain ageing kinetics is given based on a generalized form of the Harper model taking into account the diffusion of carbon atoms in the stress field of a dislocation, progressive carbon depletion in the matrix and saturation of the available dislocation sites. -the plastic instabilities propagation during tensile testing according to Piobert–Lüders phenomenon using the finite element method. A local mechanical behaviour is introduced whose shape schematically describes the local dislocation behaviour. The effect of the grain size on the velocity of the Lüders’ band front is especially enlightened. -the effect of ageing process on dent resistance. To do so, a physical extension of the former approach to more complex loading paths is proposed.

Abstract: A study was carried out on a ECAP processed Sc-containing Al-Mg-Si alloy and on a reference 6082 alloy to investigated grain structure evolution during severe plastic deformation and post-ECAP aging behaviour. The results showed that the mechanism of ultrafine structure development was substantially unchanged with respect to a reference Sc-free alloy. Also the aging sequence and precipitation kinetics of the two alloys revealed to be comparable. The ECAP processed samples of the 6082 reference alloy showed a clear recrystallization peak at temperatures in the range 315-360°C, depending on the amount of strain experienced, whereas the Sc-containing alloy retained its ultrafine structure up to temperatures well exceeding 450°C, under the conditions reproduced in a DSC temperature scan.