Determination of the individual phase properties from the measured grid indentation data
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irí Matejícek Institute of Plasma Physics, The Czech Academy of Sciences, 182 00 Praha, Czech Republic (Received 9 June 2016; accepted 16 September 2016)
Statistical distribution of grid indentation data measured in multiphase materials can be significantly affected by the presence of an interface between adjacent materials. The influence of an interface on the distribution of measured indentation moduli was therefore characterized in model metal–metal, ceramic–ceramic, and metal-ceramic composites. The change of properties near the interface was simulated by finite element method and experimentally verified by indentation in proximity of the boundary between two phases with distinctly different mechanical properties varying the depth of penetration and the distance from the interface. Subsequently, the conditional probability of measuring near the interface was quantified by beta distribution function with parameters dependent on the size of the volume/area affected by the presence of the interface. Using this approach, the intrinsic properties of the individual materials were successfully extracted from the experimental grid indentation data.
I. INTRODUCTION
Instrumented (depth-sensing) indentation is extensively used nowadays for the characterization of local mechanical properties of various materials including metals, ceramics, polymers, or composites.1 This method can be performed on very small and/or thin specimens by applying very small loads resulting in depths at the nanometer scale.2 The principal goal of this method is to extract hardness and Young’s modulus from the indenter load versus depth of penetration profile. The most commonly used method is the Oliver and Pharr method3,4 which forms the basis for the instrumented indentation testing standard [ISO 14577 (Ref. 5)]. This procedure is founded upon elastic solution of contact problem (Sneddon’s solution6). An underlying assumption of this method is that the indented solid body is homogeneous and isotropic. When indenting in proximity of an interface between two phases with different properties, this assumption is no longer valid. However, the instrumented indentation of structurally heterogeneous materials using Oliver–Pharr method is frequently used to characterize the properties of individual phases as this method is simple and available in practically all commercial devices.
Contributing Editor: George M. Pharr a) Address all correspondence to this author. e-mail: petr.hausild@fjfi.cvut.cz DOI: 10.1557/jmr.2016.375
One way of characterizing the microstructurally heterogeneous materials is the positioning of isolated indentations (e.g., with the aid of light microscopy) inside the individual phases, sufficiently far from the interface, which permits to obtain the properties of single phases. Another way is the grid indentation which is based on performing a large number of equidistantly spaced indentations and their statistical evaluation.7,8 Both methods need the knowledge of so called indentation length scale since it has been shown many times that
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