Applicability Evaluation of Young's Modulus Measurement using Equivalent Indentation Strain in Spherical Indentation Testing for Soft Materials

Abstract

Spherical indentation testing is used to measure the mechanical properties of materials because of its convenience and low-invasiveness. A method based on the Hertz theory is one of the wellknown methods used to verify the reliability of this testing technique, but it cannot be applied in the case of soft materials with a finite thickness and large deformation. In this paper, Young's modulus measurement using equivalent indentation strain in spherical indentation testing is carried out to evaluate the applicability of this measurement method for various specimens such as soft materials, biological tissues, and so on. In particular, the applicability of this method is validated by using some type of indenters and materials under different experimental conditions. The effects of the types on the relationship between the specimen thickness, indenter diameter, and specimen hardness are studied to formulate a function of Young's modulus and the diameter. The formulated results are evaluated by comparing between experimental and simulation results, and it is shown that the Young's modulus of soft materials with a finite thickness can be measured by the spherical indentation testing technique with the measurement method using equivalent indentation strain.