Chrystelle BERNARD（新領域創成研究部 助教）
フランス、サン・マルタン・デール、Science et Ingénierie des Matériaux et Procédés（SIMaP）
From September 3rd to October 31th, with the support of the Frontier Research Institute for Interdisciplinary Sciences (FRIS) international collaboration program 2018, I collaborate as visiting researcher with the University of Grenoble, and more precisely, with the Laboratoire des Science et Ingénierie des Matériaux et Procédés (SIMaP) and the Laboratoire des Ecoulements Géophysiques et Industriels (LEGI). The aim of this collaborative research was (i) to investigate the resistance to hydrodynamic cavitation of specific polymeric materials, such as Ultra High Molecular Weight PolyEthylene (UHMWPE) and (ii) to establish direct collaborations between Tohoku University and University of Grenoble. It was my first time in Grenoble and I was surprised to see how much the autumn in this city can resemble to the one we found in Japan with the autumn leaves, and even snow on the mountain at the end of my stay.
LEGI and SIMaP have a long experience in dealing with hydrodynamic cavitation erosion problems, especially against metallic substrates, using the hydrodynamic cavitation tunnel, named PREVERO. Hydrodynamic cavitation consists in the implosion of a vapor bubble near a material surface, which induces a shockwave leading to serious damage on that surface. However, previous experimental research (Deplancke et al., Wear 2015) shows that UHMWPE can resist very well to hydrodynamic cavitation.
It is of a prime interest to simulate and predict the degradation and failure of the material during such phenomenon. Thus, SIMaP developed 2D-axisymetric code based on SPH particles for both the fluid and solid to simulate hydrodynamic cavitation problems. They used the Johnson-Cook model with damage behaviour to predict the thermomechanical behaviour of the solid metallic substrate.
In the context of my work in Tohoku University, I developed a three-dimensional thermomechanical model for the prediction of the large strain behaviour of UHMWPE over large range of strain rates. Thus, the aim of the project with Grenoble University can be decomposed in the following steps: (i) hydrodynamic cavitation simulations on polymer substrate, (ii) hydrodynamic cavitation simulations on metallic substrate with polymer coating, with influence of the coating thickness and coating properties (polymer molecular weight) on the substrate damage, (iii) characterization of the polymer damage which depends on the molecular weight of the polymer.
The first step seems simple but constitutes one of the main challenges of this research. Indeed, it seems that we just have to replace the constitutive equations used for the metallic substrate (Johnson-Cook model) with our own constitutive equations developed for polymers. However, it is necessary to mention that both codes are homemade, one is 2D axisymmetric, the other one is 3D, and the coding syntax between the two developers is highly different. Thus, after a preliminary work to adapt our constitutive equation to the syntax of the 2D axisymmetric SPH code, hydrodynamic cavitation simulations were carried out.
In the future, the introduction of coating layer will be introduced in addition to the metallic substrate to investigate the efficiency of the coating on the substrate protection. While in the meantime, we will improve damage model by accounting for the polymer behaviour. This project is in fact part of the ANR CARAPACE founded by French National Research Agency between Grenoble and Lyon, who we already collaborate with on the adhesion between UHMWPE particles and metallic substrate. Thus, this grant was the perfect occasion to visit the other partners of the project and start working together on the second aspect of the project (hydrodynamic cavitation). Moreover, we will continue further this collaboration to simulate hydrodynamic cavitation on polymer-metallic substrate, which will lead to, I am sure, interesting results and scientific papers.
To finish, I would like to express my gratitude to International collaboration program 2018 and FRIS office, which provides us generous support with this opportunity.
Thank you very much!
写真左：Grenoble by night
写真右：Hydrodynamic cavitation tunnel (PREVERO) of LEGI.
Metallic sample submitted to hydrodynamic cavitation in PREVERO device