PhD defence of Zhongfeng Xu

Multi-Scale Study of Polyamide-12 Additive Manufacturing by L-PBF Process: from Experimental Characterization to Numerical Simulation

Zhongfeng Xu conducted his PhD research in the S&P and 2MS research teams, under the supervision of Jean-Luc Bouvard and Yancheng Zhang.

He will defend his PhD in Computational Mechanics and Materials on December 20th, 2024, in front of the following jury:

M. Shihe XIN INSA Lyon Rapporteur

M. Modesar SHAKOOR IMT Nord Europe Rapporteur

Mme Claire BARRES INSA Lyon Examinatrice

M. RYCKELYNCK DAVID MINES Paris-PSL Examinateur

Mme Luisa ROCHA DA SILVA Ecole Centrale de Nantes Examinatrice

M. Jean-Luc BOUVARD MINES Paris-PSL Examinateur

M. Yancheng ZHANG MINES Paris-PSL Examinateur

M. Marcos BATISTELLA IMT Mines Alès Examinateur

Mme Noëlle BILLON MINES Paris-PSL Invitée

M. Lionel FREIRE MINES Paris-PSL Invité

Abstract:

The Laser Powder Bed Fusion (L-PBF) additive manufacturing (AM) process, which produces parts by selectively scanning powder materials with a laser beam, has been applied to semi-crystalline polymers. Due to the layer-by-layer nature of forming, the potential of this innovative process lies in the production of complex geometries, and reducing product development time. However, the application of L-PBF in the manufacture of semi-crystalline polymers is still limited. On the one hand, the complex material behavior, the diversity of powder organization, and the processing conditions related to many machine parameters pose difficulties for manufacturing optimization. On the other hand, the lack of an external driving force makes reproducibility more difficult compared to conventional methods. Specifically, manufacturing of optimized parts by AM, which possess comparable mechanical properties and dimensional stability with traditional methods, is the long-term goal of the semi-crystalline polymers L-PBF community. In this study, the most widely used commercially available polymer, polyamide-12 (PA12), was selected. First, the basic material properties, including thermal property, rheology property, mechanical property, and particle morphology, were thoroughly investigated by experiments and mathematically modeled. Then, the particle coalescence in the melt pool and following crystallization with different processing parameters is studied based on the particle scale finite element numerical model. In a continuum mesoscale model, the density evolution and the consequent melt pool contraction due to powder consolidation have been numerically studied using the level set method and validated with experimental measurements. Numerical studies suggest that the thermal interaction between adjacent tracks has an important influence on the melt pool evolution. At the macroscale, the warping mechanisms associated with thermal dilatation and phase transformation-induced non-uniform volume shrinkage was investigated. In addition, the constitutive law of viscoelasticity has been developed and implemented at different temperatures by the time-temperature superposition principle. Then, the phase transformation governed by the modified crystallization kinetics, displacement and stress evolution during the L-PBF process were simulated. This study demonstrates a systematic material characterization and multi-scale multiphysics numerical modeling. It can be easily extended to other semi-crystalline polymers for L-PBF process simulation and optimization.

Keywords: Additive manufacturing, Polyamide-12, Experimental characterization, Numerical modeling