Multiple-frequency dynamic nanoindentation testing

A new method of dynamic nanoindentation testing is introduced in this paper. Conventional dynamic nanoindentation testing involves the superposition of a single frequency sinusoidal force or displacement onto the quasi-static load–displacement curve. However, the viscoelastic response of many materials depends upon the frequency of the deformation of the material. This paper describes a method whereby the storage and loss modulus of viscoelastic solids can be determined using a multi-frequency dynamic oscillatory motion mode of deformation. In this method, the applied load is modulated by a pseudo-random force signal comprising multiple frequencies. A Fourier analysis is then used to deconvolute the signal into frequency-dependent values of storage and loss modulus for the specimen material as a function of frequency. The instrument response is cancelled by the use of a reference transfer function using an equalization process. Established modeling equations can then be used to extract the modulus of elasticity and the viscosity of the specimen material.