Micro hardness determination on a rough surface by using combined indentation and topography measurements

Abstract

Micro hardness determination on rough surfaces is a topic of interest e.g. in industrial applications where the component surface is of functional relevance. In most approaches, hardness on a rough surface is determined by including profile roughness parameters like R a (e.g., [1][2][3][4][5]) to adjust measured hardness values or to get the minimum indentation depth value where the influence of the surface topography is assumed to become negligibly small. In the present study, local surface topography data were used instead to enable precise micro hardness measurements on a sample with arbitrary surface topography. Samples made of 1.457 1 stainless steel with different surface states were face milled by using an end mill with different feed rates. Instrumented indentation tests were performed on these samples as well as on comparative samples with polished surfaces. From the resulting load-indentation depth (F-d)-curves the averaged indentation hardness was calculated for all surface states. A method was applied to manipulate and to average the F-d-curves to eliminate deviations, occurring at the beginning of the indentation. The indentation hardness was calculated from these modified F-d-curves and compared to the indentation hardness from the actually measured F-d-curves of the polished samples with feasible results. Using surface topography measurements is considered to enable deriving more accurate indentation hardness values directly and to put the investigations to another level. The surface topography of the samples was evaluated by confocal microscope measurements before and after the indentation tests. From the surface topography data at the location of indentation, four parameters were calculated: volume, projected contact area and depth of the indentation mark, as well as the curvature of the surface topography before indentation. These parameters were correlated with the hardness value from the respective indentation and compared to the indentation hardness of the polished sample. The results of the present study are the basis for combining optical imaging techniques like confocal microscopy or white light interferometry and indentation testing equipment to broaden the field of application.

Spirulina‐based composites for 3D‐printing

“…This approach allows for capturing the material properties statistically within the measured range of data. 41,42,43…”

“…The scatter in the modulus and hardness values within each sample group reflect the literature-reported effects of surface roughness on the nanoindentation tests. 41,42,70 In order to evaluate how the two properties vary across the sample groups, instead of comparing only the mean values, we apply a Welch's t test thus evaluating the entire data distributions. This statistical test enables comparative assessment of distributions with unequal variances, as the ones observed from our tests.…”

The influence of tool’s surface topography on mechanical properties of injection moulded product

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“…The indentation modulus (E IT ) was calculated from the plane strain modulus (E * ) using an estimated Poisson's ratio (ν s ) of the sample (Polymer 0.3 to 0.4) [25,27].…”

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