Personne : Deteix, Jean
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Université Laval. Département de mathématiques et de statistique
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- PublicationAccès libreSensitivity study of a numerical model of heat and mass transfer involved during the medium-density fiberboard hot pressing process(Society of Wood Science and Technology, 2010-04-01) Deteix, Jean; Cloutier, Alain; Fortin, André; Kavazovic, Zanin.The objective of this work was to estimate the impact of the variability of the mediumdensity fiberboard mat heat and moisture transfer properties on the results predicted by a numerical model of hot pressing. The three state variables of the model, temperature, air pressure, and vapor pressure, depend on parameters describing the material properties of the mat known with a limited degree of precision. Moreover, different moisture sorption models and initial moisture contents also have an impact on the numerically predicted results. In this sensitivity study, we determined the impact of variations of the mat properties, sorption models, boundary conditions, and initial MC on the state variables. Our study shows that mat thermal conductivity, convective mass transfer coefficient of the external boundary, and gas permeability have the most significant impact on temperature, gas pressure, and MC within the mat. On the other hand, the convective heat transfer coefficient of the external boundary has no impact on the state variables. The sorption model affects significantly mat MC predictions only. The initial MC of the mat has a strong influence on the internal gas pressure.
- PublicationAccès libreMinimizing flooring strip weight : a shape optimization approach(North Carolina State University * College of Natural Resources, 2012-05-01) Deteix, Jean; Cloutier, Alain; Fortin, André; Djoumna, Georges; Blanchet, PierreIn North America, flooring strips are manufactured with grooves at the back. There are various reasons for these grooves but, historically, they were considered a strategy to reduce weight and transportation costs as well as improving dimensional stability. As no data are available to assess best practices in terms of performance, we have investigated methods to reduce flooring strip weight. One way to achieve this is to adjust the number and shape of grooves. Using warp as a comparison tool, we were able to analyze the merits of a finite number of designs. With this approach, however, we could not guarantee that the result was the most favourable. The search for a solution led to design optimization, i.e.: minimizing weight by acting upon a part of the strip’s shape, taking into account its warp resistance or stiffness. This paper describes an optimization strategy adapted to the calculation of the optimal design subjected to arbitrary mechanical and geometrical conditions (including the thickness of the wear layer). This approach is not limited to flooring strips, and it can be used in any situation where a linear hygromechanical model is relevant. This strategy involves two steps: global optimization with respect to admissible variations of the shape (or design) followed by a post-processing phase that takes into account various other mechanical and possibly geometrical conditions imposed on the strip. This paper describes an optimization strategy adapted to the calculation of the optimal design subjected to arbitrary mechanical and geometrical conditions (including the thickness of the wear layer). This approach is not limited to flooring strips, and it can be used in any situation where a linear hygromechanical model is relevant. This strategy involves two steps: global optimization with respect to admissible variations of the shape (or design) followed by a post-processing phase that takes into account various other mechanical and possibly geometrical conditions imposed on the strip.
- PublicationAccès libreNumerical modeling of the medium-density fiberboard hot pressing process.Part 2, Coupled mechanical and heat and mass transfer models(Society of Wood Science and Technology, 2012-07-01) Deteix, Jean; Cloutier, Alain; Fortin, André; Kavazovic, Zanin.In this study, coupled mechanical and heat and mass transfer models describing mat compression and heat and moisture transfer occurring during hot pressing of medium-density fiberboard mats are presented. The mat is considered an aging linear elastic material and is described by a mechanical model in three dimensions. Rheological properties of the mat depended on time, space, temperature, moisture content, and resin cure. Hardening and softening phases of the material behavior were accounted for and treated with separate constitutive laws. Press closing was taken into account, and a coupling procedure between mechanical and heat and mass transfer models was elaborated. Development of the vertical density profile was dynamically predicted by the model. Both mechanical and heat and mass transfer models were discretized in space by the finite element method. An implicit second-order backward finite difference scheme was used for time discretization. All calculations were carried out on a moving geometry whose deformation (compression) was a function of a press closing schedule. Model results exhibited good agreement with experimental results. Under various press closing schedules, the model gave information on variables such as density profile, total gas pressure, air and vapor pressure, temperature, moisture content, RH, and degree of resin cure.
- PublicationAccès libreNumerical modeling of the medium-density fiberboard hot pressing process. Part 1, Coupled heat and mass transfer model(Society of Wood Science and Technology, 2012-04-01) Deteix, Jean; Cloutier, Alain; Fortin, André; Kavazovic, Zanin.A mathematical model describing heat and moisture transfer during hot pressing of mediumdensity fiberboard mats is presented. The model is based on conservation of energy, air mass, and water vapor mass, resulting in a three-dimensional unsteady-state problem in which mat properties and state variables vary in time and space. The conservation equations are expressed as functions of the three state variables: temperature, air pressure, and vapor pressure. The model includes conductive and convective heat transfer, phase change of water, and convective and diffusive mass transfer. Resin curing kinetics and latent heat associated with phase change of water are also taken into account. The closing of the batch press and development of the density profile are taken into account by imposing a predefined time- and space-dependent density profile. Calculations are carried out on reference geometry, and mathematical details relevant to the transfer from actual to reference geometry are presented. The system is discretized in space by the finite element method and in time by the Euler implicit scheme. The results exhibit good agreement with experimental measurements and provide information on variables of interest such as total gas pressure, temperature, moisture content, RH, and resin cure.
- PublicationRestreintMoisture-induced stresses in engineered wood flooring with OSB substrate(Springer, 2012-03-08) Deteix, Jean; Barbuta, Costel; Cloutier, Alain; Fortin, André; Blanchet, PierreEngineered wood flooring (EWF) is a multilayer composite flooring product. The cross layered structure is designed to give good dimensional stability to the EWF under changing environmental conditions. However, during winter season in North America, the indoor relative humidity could decrease dramatically and generate an important cupping deformation. The main objective of this study was to characterize the interlaminar stresses (σ 33, σ 13 and σ 23) distribution at free-edges in EWF made with an OSB substrate. A three-dimensional (3D) finite element model was used to predict the cupping deformation and to characterize stresses developed in the EWF. The finite element model is based on an unsteady-state moisture transfer equation, a mechanical equilibrium equation and an elastic constitutive law. The physical and mechanical properties of OSB substrate were experimentally determined as a function of the density and moisture content. The simulated EWF deformations were compared against the laboratory observations. For both simulation and experimental results, the cupping deformation of EWF was induced by varying the ambient relative humidity from 50 to 20% at 20°C. A good agreement has been found between the numerical and experimental EWF cupping deformation. The stress distribution fields generated by the model correspond to the delaminations observed on the OSB substrate in the climate room. Delamination in EWF can occur principally under the action of the tension stress or a combination of tension and shear stresses. Finally, simulated results show that the levels of interlaminar stresses are maximal near the free-edges of EWF strips.