Dimensionless analysis of the elastoplastic constitutive properties of single/multilayered films under nanoindentation

Among the features of substrate-film structures, based on the load-displacement curves obtained from the nanoindentation tests, the intrinsic parameters of film material (elastic modulus, hardening exponent, and yield strength) are considered as the influential parameters in the load-displacement curves in terms of the applied load and work done in the loading phase. Based on the influential parameters combined in a dimensionless manner, the dimensionless function formulations are presented in association with the finite element simulation results, leading to a novel methodology proposed to solve the constitutive parameters appropriate for single-layered elastoplastic film materials. The advantage of the proposed dimensionless function in reproducing the finite element prediction results is verified by comparing it with the constitutive parameters predicted by machine learning algorithms based on the vast indentation data. In addition, by proposing the concept of "composite constitutive parameters", the constitutive parameters of unknown single-layered films are established using a layer-by-layer strategy based on finite element simulations, followed by the subsequent determination of the constitutive parameters of multilayered films. The current work on the mechanical properties of multilayered films holds significant potential in improving the reliability and lifetime of the systems and devices based on thin film technology.