Modeling and analysis of material behavior during cavitation erosion
ury members
Mrs. Veronique FAVIER, Professor, Arts et Métiers ParisTech, PIMM, Reviewer
Mr. Sofiane KHELLADI, Professor, Arts et Métiers ParisTech, DynFluid, Reviewer
Mrs. Regiane FORTES-PATELLA, Professor, Univ. Grenoble Alpes, LEGI, Examiner
Mr. Ayat KARIMI, Doctorate, Ecole Polytechnique Fédérale de Lausanne, ICMP, Examiner
Mr. Marc FIVEL, Director of Research CNRS, Univ. Grenoble Alpes, SIMaP, Supervisor
Mr. Jean-Pierre FRANC, Director of Research CNRS, Univ. Grenoble Alpes, LEGI, Co-supervisor
Mr. Christian PELLONE, Researcher CNRS, Univ. Grenoble Alpes, LEGI, Invited
Abstract
Numerical prediction of cavitation erosion requires the knowledge of flow aggressiveness, both of which have been challenging issues till-date. This thesis proposes to use an inverse method to estimate the aggressiveness of the flow from the observation of the pits printed on the surface in the first moments of the cavitation erosion. Three materials were tested in the same experimental conditions in the cavitation tunnel PREVERO available in LEGI Grenoble. The geometry of the pits left on the surface is precisely measured using a systematic method to overcome the roughness effect. Assuming that each pit was generated by a single bubble collapse whose pressure field is treated as a Gaussian shape, finite element calculations are run for estimating the load that created each residual imprint. It is shown that the load distribution falls on a master curve independent of the tested material; the softer material (aluminum alloy) measuring the lowest impacts while the most resistant material (duplex stainless steel) provides access to the largest impact pressures. It is concluded that the material can be used as a pressure sensor measuring the level of aggressiveness of the flow. The inverse method is based on a material characterization taking into account strain rate effects. It is shown that nanoindentation tests are more suitable than compression tests to determine the parameters of the behavior law, particularly for the aluminum alloy for which the microstructure is very heterogeneous. High-speed compression tests with split Hopkinson pressure bars complement the constitutive law giving the sensitivity to the strain rate. Simulations considering the dynamic loading show that impacts of strong amplitude but applied in a short time do not leave any residual pit if the frequency is higher than the natural frequency of the material treated as a damped oscillator. A dynamic mechanism of plastic strain accumulation that could eventually lead to fatigue failure is proposed. Finally, the mass loss curve of cavitation erosion is simulated by applying randomly on a 3D mesh, the impact force population estimated by the inverse method.
Key words :
Cavitation erosion; Finite element modeling; Material characterization, Impact load measurement; Cavitation fatigue, Mass-loss prediction