Optimization of experimental parameters for the mechanical characterization of thin elastic films

Abstract

Indentation experiments are a common tool to measure the elastic properties of many different kinds of samples. However, only few techniques are available to measure the elastic modulus and the Poisson ratio of thin elastic films. Recently, we have described a novel technique based on the steel sphere method to simultaneously measure both parameters of a thin elastic film in a single experiment by placing millimeter-sized steel spheres on the films. In this work, we investigate how various measurement parameters can be tuned to increase the measurement accuracy significantly. These parameters include the number, size, and density of the spheres, the number of data points per sphere and the film thickness. With experiments and simulations we demonstrate that the precision of the measurement can be improved drastically if the parameters are chosen appropriately. We show how to adjust the number of data points to achieve a good balance between workload and accuracy. Additionally, the accuracy can be improved by covering a wide range of different indentation geometries. In particular the use of larger spheres and spheres with a higher density is generally more favorable. We provide Java software to easily adopt the technique and to simplify the data analysis.