Matthieu Zinet

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.

Analysis of the Microstructure of Polymers With Regard to Their Thermomechanical History: STHM and DSC Measurements

The variation of the microstructure within the thickness of moulding plates of two semicrystalline polymers, an isotactic Poly-Propylene and a Poly-Butylene Terephtalate, was observed by optical microscopy technique. These observations allowed specifying the different zones of iso-microstructure within the plate thickness, commonly called “skin zone”, “shear zone”, “post filling zone ”and“ core zone”in terms of crystallite size and zone thickness. The variation of the melting temperature was then analysed by using a local thermal analysis method based on the scanning thermal microscopy technique in each of these zones. Our results show the expected link between the local microstructure and the polymer melting temperature. They also highlight a strong coupling between the microstructure, the material and its processing conditions.Copyright

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.

Competition of Flow and Thermal Effects During Crystallization of Polymers: Influence on Morphology

It is well known that the properties of polymer products are strongly dependent on the thermo‐mechanical history experienced by the material during processing. In the particular case of semicrystalline polymers, flow‐induced crystallization is known to have a major effect on crystalline morphology and consequently on structural heterogeneities such as shrinkage. In that context, a model based on the assumption that flow‐induced nucleation is linked to the trace of the deviatoric stress tensor was developed to represent both the effects of thermal‐ and flow‐induced nucleation on the polymer final crystallinity. In the present work, this model is applied to an isotactic polypropylene (iPP) in isothermal and non‐isothermal Couette flow configurations. We focus on the competition between thermal and flow effects on the crystallization rate. We study the influence of the competition on morphology for different processing conditions. We obtain in each case the crystalline fraction due to thermal and flow effect...

Simulation of Polymer Crystallization: Role of the Visco-Elasticity

In polymer processing, it is established that the flow causes the polymer chains to stretch and store the energy, by changing their quiescent state free energy. Koscher et al. [1] presented in 2002 an experimental work concerning the flow induced crystallization. They made the assumption that the polymer melt elasticity, quantified by the first normal stress difference, is the driving force of flow-induced extra nucleation. In their work, a constant shear stress is considered, and the first normal stress difference agrees with the use of the trace of the stress tensor. The stored energy due to the flow “Δ Ge” is commonly called elastic free energy and associated to the change in conformational tensor due to flow. By extending the Marrucci theory [2], several studies link this Δ Ge to the trace of the deviatoric stress tensor (first invariant). In this paper, a numerical model able to simulate polymer crystallization is developed. It is based on the assumption that flow induced extra nucleation is linked to the trace of the deviatoric stress tensor. Thus a viscoelastic constitutive equation, the multimode Upper Convected Maxwell (UCM) model, is used to express the viscoelastic extra-stress tensor τVE , and a damping function is introduced in order to take into account the nonlinear viscoelasticity of the material. In Koscher’s work [1], the integral formulation of the Upper Convected Maxwell (UCM) model is used too, but without any damping function, i.e. they assume that the polymer behaves as linear viscoelastic. As an application, a 2D isothermal flow configuration between two plates is simulated. A comparison between the proposed model and the Koscher’s one is then performed, and interesting resultes are pesented: without introducing a damping function, the two models give similar results in the same configurations, but the introduction of a damping function leads to important discrepancies between the two models, seeming that the assumption of a linear viscoelastic behavior is not realistic when the fluid strain and/or stresses are greater than a given values.Copyright