45,717 research outputs found
A design-for-casting integrated approach based on rapid simulation and modulus criterion
This paper presents a new approach to the design of cast components and their associated tools. The current methodology is analysed through a case study and its main disadvantages underlined. Then, in order to overcome these identified drawbacks, a new approach is proposed. Knowing that this approach is mainly based on a rapid simulation of the process, basics of a simplified physical model of solidification are presented as well as an associated modulus criterion. Finally, technical matters for a software prototype regarding the implementation of this Rapid Simulation Approach (RSA) in a CAD environment are detailed
Equivalent thermo-mechanical parameters for perfect crystals
Thermo-elastic behavior of perfect single crystal is considered. The crystal
is represented as a set of interacting particles (atoms). The approach for
determination of equivalent continuum values for the discrete system is
proposed. Averaging of equations of particles' motion and long wave
approximation are used in order to make link between the discrete system and
equivalent continuum. Basic balance equations for equivalent continuum are
derived from microscopic equations. Macroscopic values such as Piola and Cauchy
stress tensors and heat flux are represented via microscopic parameters.
Connection between the heat flux and temperature is discussed. Equation of
state in Mie-Gruneisen form connecting Cauchy stress tensor with deformation
gradient and thermal energy is obtained from microscopic considerations.Comment: To be published in proceedings of IUTAM Simposium on "Vibration
Analysis of Structures with Uncertainties", 2009; 14 pages
Modeling of Nucleation Processes
Nucleation is the onset of a first-order phase transition by which a
metastable phase transforms into a more stable one. Such a phase transition
occurs when an initial system initially in equilibrium is destabilized by the
change of an external parameter like the temperature or the pressure. If the
perturbation is small enough, the system does not become unstable but rather
stays metastable. In diffusive transformations, the system then evolves through
the nucleation, the growth and the coarsening of a second phase. Such a phase
transformation is found in a lot of situations in materials science like
condensation of liquid droplets from a supersaturated vapor, solidification,
precipitation from a supersaturated solid solution, ... The initial stage of
all these different processes can be well described within the same framework.
Since its initial formulation in 1927 by Volmer, Weber and Farkas and its
modification in 1935 by Becker and D\"oring the classical nucleation theory has
been a suitable tool to model the nucleation stage in phase transformations. In
this article, we first describe this theory. A kinetic approach, the cluster
dynamics, can also be used to describe nucleation. This constitutes the second
part of this article. The links as well as the difference between both
descriptions are emphasized. Since its initial formulation, the classical
nucleation theory has been enriched, so as to take into account the fact that
clusters other than monomers can migrate and react. It has been also extended
to multi-component systems. These generalizations of the initial formalism are
also presented
Digital waveguide modeling for wind instruments: building a state-space representation based on the Webster-Lokshin model
This paper deals with digital waveguide modeling of wind instruments. It presents the application of state-space representations for the refined acoustic model of Webster-Lokshin. This acoustic model describes the propagation of longitudinal waves in axisymmetric acoustic pipes with a varying cross-section, visco-thermal losses at the walls, and without assuming planar or spherical waves. Moreover, three types of discontinuities of the shape can be taken into account (radius, slope and curvature).
The purpose of this work is to build low-cost digital simulations in the time domain based on the Webster-Lokshin model. First, decomposing a resonator into independent elementary parts and isolating delay operators lead to a Kelly-Lochbaum network of input/output systems and delays. Second, for a systematic assembling of elements, their state-space representations are derived in discrete time. Then, standard tools of automatic control are used to reduce the complexity of digital simulations in the time domain. The method is applied to a real trombone, and results of simulations are presented and compared with measurements. This method seems to be a promising approach in term of modularity, complexity of calculation and accuracy, for any acoustic resonators based on tubes
Latent curing of epoxy-thiol thermosets
Epoxy-thiol curing is a click reaction which allows quantitative yield of the end products. The base-catalyzed reaction is rapid at low temperatures so it is most often desirable to harness reactivity by using latent catalysts. In this work, we used triazabicyclodecene tetraphenylborate (TBD·HBPh4) as a photobase generator (PB). We activated the PB either thermally or by UV light and monitored reaction kinetics by DSC and FTIR methods. Depending on the catalytic system used, the rate of the thiol-epoxy reaction was ordered as follows: Neat base > UV activated PB > thermally activated PB > uncatalyzed system. A series of isothermal and non-isothermal DSC experiments were run on non-irradiated and irradiated samples in order to study the effect of PB content and UV irradiation duration on PB activation efficiency and latency/storage stability. The data from DSC were analyzed using model-free linear isoconversional methods to estimate kinetic parameters such as activation energies. In addition, the kinetics data for both activation methods were shown to be accurately represented by multi-term Kamal models. The storage stability of the systems were studied at room temperature and was shown to fit well to the predictions of the kinetic model.Postprint (author's final draft
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