Application of spherical nanoindentation to determine the pressure of cavitation impacts from pitting tests
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Jean-Pierre Franc Laboratory of Geophysical and Industrial Flows (LEGI), Grenoble Institute of Technology, 38041 Grenoble Cedex 9, Grenoble, France (Received 4 May 2011; accepted 4 August 2011)
This article focuses on the use of spherical nanoindentation measurements to estimate the pressure of cavitation impacts and its statistical distribution. Indeed, nanoindentation techniques are supposed to represent an effective tool in this field due to the similarities between substrate deformation under liquid impact and indentation testing. First, nanoindentation experiments were used to extract the mechanical parameters of a Nickel–Aluminum–Bronze alloy; second, pitting tests were performed at different operating pressures, and the geometrical characteristics of the pits were measured; and finally, the spectra of impact pressure and loads responsible for material erosion were obtained by coupling the findings of indentation tests with the analysis of pitting tests. Results assessed the capability of the proposed methodology to quantify the hydrodynamic aggressiveness of the cavitating flow. This procedure, which assumes the material itself as a sensor that is able to detect the impact loads, could represent an alternative solution to pressure transducers in estimating the cavitation intensity. I. INTRODUCTION
Cavitation erosion is a particular form of material damage caused by the collapse of gas bubbles on a metal surface.1–4 This collapse, which is usually associated to abrupt variations in pressure related to the fluid hydrodynamics, exerts on solid surfaces nearby a particular solicitation characterized by repeated and randomly distributed stress pulses of several hundreds of megapascal in pressure. The result is an extended damage of the surface characterized by small holes, named cavitation pits, with characteristic dimensions in the order of several tens of micrometer and whose accumulation can lead to the material failure. One of the main issues in cavitation erosion is the estimation of the cavitation intensity or flow aggressiveness of a cavitating flow. This could be used for the prediction of material mass loss as a function of exposure time by proper modeling of the material response to cavitation erosion impacts.5–7 In this light, knowledge of the spectrum of impact loads is essential due to its capability to provide useful information on the flow aggressiveness. Conventional pressure sensors are commonly adopted to extract this information by mounting them in an appropriate location of a target material subjected to an erosion test. Even if a lot of efforts have been made in recent years to a)
Address all correspondence to this author. e-mail: davide.carnelli@epfl.ch DOI: 10.1557/jmr.2011.259 J. Mater. Res., Vol. 27, No. 1, Jan 14, 2012
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develop reliable techniques for the direct measurement of cavitation collapse pulses,7–11 some issues are still present, as the sensors’ size is big compared to collapse size, they may not necessarily meet the required con
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