Identification of elastic parameters of transversely isotropic thin films by combining nanoindentation and FEM analysis

We develop the nanoindentation method to identify the elastic parameters of transversely isotropic thin films by combining nanoindentation test with finite element method (FEM) simulation. In the forward analysis, CAX4R and CAX4E element types of ABAQUS are used to simulate the purely mechanical indentation and the piezoelectric indentation. With assistance of the substrate effect, the numerical results give indentation responses at the moderate ratio of penetration depth to film thickness, and the dimensionless equations between the maximum indentation load, loading curve exponent and the elastic parameters of film/substrate system are established by extensive FEM simulations. In the reverse analysis, the nanoindentation test is performed on ZnO thin film as transversely isotropic material, and the experimental indentation curves can be fitted as the power function. The maximum indentation load and the loading curve exponent can be obtained from the experimental indentation curves and substituted into the dimensionless equations to obtain the elastic parameters of ZnO thin film. The results show the transverse Young’s modulus, the longitudinal Young’s modulus, and the longitudinal shear modulus under the piezoelectric indentation mode are closer to the experimental values measured by the acoustic method than those under the purely mechanical indentation mode. This study develops the nanoindentation method to extract the elastic parameters of transversely isotropic thin films, and it may be helpful to the measurement of thin film mechanical properties by means of nanoindentation.