Indenting fractal-edged elastic materials

TL;DR

This paper investigates how fractal surface roughness affects the measurement of elastic properties in soft materials during indentation, revealing significant variations in measured Young's modulus due to surface geometry.

Contribution

It introduces a computational model incorporating fractal geometry to analyze the impact of surface roughness on elastic property measurements in indentation experiments.

Findings

Fractal surface roughness can alter measured elastic moduli by up to 40%.

Surface roughness effects are more pronounced when fractal dimensions are comparable to sample size.

Inclusion of fractal geometry improves understanding of experimental measurement variability.

Abstract

Surface roughness plays a crucial role in the accuracy of indentation experiments used to measure the elastic properties of materials. In this study, we present a computational analysis of how surface roughness, represented explicitly by fractal geometry, influences the mechanical properties of soft materials. We model two-dimensional elastic samples with a Koch fractal bottom surface, grown upward or downward to the fourth generation, referred to as fractal \textit{down} and fractal \textit{up}, respectively. The elastodynamics equations are solved numerically while a rigid punch indents the elastic sample from the top surface. By applying the Hertz model for mechanical contact, we determine the Young's modulus of the materials. Our findings reveal that fractal surfaces, especially those with dimensions comparable to the sample size, can significantly alter experimental measurement outcomes. In particular, the roughness of the substrate profoundly affects the measured elastic properties, as seen in scenarios involving cell elasticity. For instance, in the \textit{down} fractal scenario, reductions in the measured elastic modulus range from 2\% to 4\%, while increases reach up to 40\% in the \textit{up} fractal scenario. These results underscore the importance of incorporating fractal geometry into the design and analysis of indentation experiments. This approach could significantly enhance our understanding and application of material characterization and mechanical testing, leading to more accurate and reliable results.