Mhamed Boutaous

Identification of the equivalent electrical model parameters and thermal properties of a LMO / Graphite battery cell for full electric vehicle

In this work, the electro-thermal behavior of a prismatic 50 Ah Lithium Manganese Oxide (LMO)/ Graphite cell is investigated. This cell is designed to be integrated in independent 12-cell modules, the global battery rack being composed of several modules. Optimal sizing of the thermal management system requires accurate knowledge end prediction of the thermal load associated with given operating conditions (current profile). It was obtained by identifying the electro-thermal model parameters for a single cell, carried out using a custom electrical bench able to impose a predefined current evolution, controllable by serial interface. From these measurements, the heating power is predicted using the Bernardi model. The identified electrical and thermal model parameters are then integrated in a 3D FEM transient simulation of the cell thermal behavior under realistic conditions.

Modeling the Radiative Heat Transfer in Selective Laser Sintering of Polymers: Scattering Effect

A numerical model, coupling radiative and conductive heat transfer in a polymer powder bed and providing a local temperature field, is proposed. To simulate the polymer sintering by laser heating as in additive manufacturing, a double-lines scanning of a laser beam over a thin layer of polymer powder is studied. An effective volumetric heat source, using a modified Monte Carlo method, is estimated from laser radiation scattering and absorption in a semi-transparent polymer powder bed. In order to quantify the laser-polymer interaction, the heating and cooling of the material is modeled and simulated with different types heat sources by both finite element method (FEM) and discrete element method (DEM). To highlight the importance of introducing the semi-transparent behavior of such materials and in order to validate our model, the results are compared with works of other researchers taken from literatures.Copyright

Towards the Enhancement of the Crystallization Kinetics of a Bio-Sourced and Biodegradable Polymer PLA (Poly (Lactic Acid))

PLA (Poly Lactic Acid) is a bio-sourced and a biodegradable polymer. It represents an interesting substitute for some petrochemical based polymers, especially because of its wide range of applications in the biomedical, agriculture and packaging fields. Unfortunately, PLA exhibits slow crystallization kinetics, limiting the amount of crystallinity in the final product, which is a handicap in order to extend its use. Many authors have investigated the crystallization of polymers; nevertheless several physical mechanisms remain not yet understood.This work aims a complete characterization of PLA in order to improve the understanding of its crystallization kinetics. The quiescent crystallization was investigated using Differential Scanning Calorimetry (DSC) measurements in isothermal and non-isothermal conditions for PLA and PLA with 5wt % talc. The flow effect on crystallization was studied using a thermocontrolled hot-stage shearing device (Linkam) coupled with an optical microscope. The number of activated nuclei and the growth rate were measured as functions of temperature. In addition, the linear viscoelastic properties were obtained from a rheometer with plate-plate geometry.The enhancement of the crystallization was quantified and analyzed in terms of the half crystallization time t1/2.This characteristic time t1/2 is found to be drastically decreased by both the talc and the flow which promote supplementary nucleation leading to various crystalline microstructures. The flow is known to orient and stretch molecules leading to an extra nucleation. An original description of this phenomenon is proposed using two characteristic Weissenberg numbers; based on the definition of Rousse and reptation times.Finally, we have proposed a semi-empirical model to quantify the thermal and flow contributions on the crystallization.Copyright

PLA Crystallization Kinetics and Morphology Development

Abstract This paper investigates the crystallization kinetics and morphology development of PLA. The transitory stages in the evolving flow-induced crystallization of PLA are identified and classified in terms of the overall crystallization kinetics and the crystalline morphologies. Under quiescent conditions, temperature governs the crystallization process and the slow crystallization kinetics of PLA is highlighted under these conditions, whereas under shearing conditions, the crystallization is highly enhanced due to the promotion of the nucleation mechanism. The enhancement of the crystallization implies also morphological modifications. Depending on the shear rate and the shearing time the microstructure changes dramatically: spherulitic microstructure, fine grained microstructure and oriented microstructure. For a specific shear rate, depending on the magnitude of the shearing time the microstructure assumes the following states: for low shearing time only an increase of the number of nuclei is observed (leading to fine grained microstructure), followed by a saturation of point-like nuclei, and for a relatively long shearing time (i. e. beyond a critical shearing time) the development of oriented structures looking like “shish-kebabs” is observed. The critical shearing time for the formation of oriented structures in PLA is determined as a function of the shear rate.

Analysis of the Process-Structure-Behavior Interaction in Bio-Sourced Polymers: Role of the Crystallization Kinetics

PLA (Poly Lactic Acid) is a bio-sourced and biodegradable polymer. It represents an alternative for polymers issued from petrochemical synthesis. Unfortunately, the crystallization kinetics of PLA is very slow and limits the possibility to extend its application in several industrials domains. The enhancement of the PLA crystallization kinetic can be obtained by addition of nucleating agents of by ordering the molecular chains during flow, as in processing conditions. During processing of thermoplastic polymer experiences several thermomechanical conditions influencing drastically its final properties and mechanical behavior. During injection molding process, macromolecules are oriented and ordered due to the shear and elongation imposed by the melt flow in the mold during the filling step. As a consequence, supplementary nucleation is created in the polymer, leading to the acceleration of the crystallization kinetics. In this work, we propose to analyze and to quantify the role of the flow, the temperature kinetics and the nucleating agent on injected PLA parts structure and their mechanical behavior. A parametric analysis of the relationship between the polymer, its structure and the processing condition will be presented. The competition (sometimes antagonism) between several parameters, as the shear rate, the temperature kinetics and the nucleating agent will be highlighted.Copyright

Structure Development of Biodegradable Polymers: Crystallization of PLA

Poly-(lactic acid) or PLA is a biodegradable polymer produced from renewable resources. Recently new polymerization routes have been discovered which allows increasing the produced quantity. Hence, PLA becomes of great interest to lessen the dependence on petroleum-based plastics. Due to its good mechanical properties, PLA is a potential substitute to some usual polymers such as PET. Nevertheless the kinetics of crystallization is relatively slow which can be an inconvenient in polymer processing. Thermomechanical history experienced by the polymer during processing affects drastically its relative crystallinity. For example, the flow is known to enhance the crystallization kinetics. Nevertheless, only a few studies were found in the literature about the crystallization of PLA under flow conditions. In the present work we investigate the crystallization of PLA under quiescent and flow conditions. A combination of DSC, rheological and optical measurements is used to identify the crystallization kinetic parameters. Thermal and flow-induced crystallization are then simulated using two sets of Schneider’s differential equations [1] based on a previously developed model Zinet & al [2]. Experimental results are analyzed and compared to the numerical model. New features about the influence of thermal and flow conditions on the crystallization of PLA are discussed.