Relationship between scratch hardness and yield strength of elastic perfectly plastic materials using finite element analysis

With thin solid film usage expanding in numerous technologies, reliable measurements of material properties such as yield strength become important. However, for thin solid films the measurement of yield strength is not readily available, and an alternative method to obtain this property is to measure hardness and convert it to yield strength. Tabor suggested dividing hardness by ∼3 to obtain yield strength, which has been used extensively, despite its shortcomings. Since the pioneering work of Tabor, researchers have performed numerical and experimental studies to investigate the relationships between hardness, yield strength, and elastic modulus, using the indentation technique. In this study, finite element analysis was performed to simulate the nanoscratch technique. Specifically, the nanoscratch finite element analysis was used to validate a previously developed analytical scratch hardness model. A full-factorial design-of-experiments was performed to determine the significant variables for the ratio of calculated scratch hardness to yield strength and a simple analytical prediction model for the ratio of hardness to yield strength was proposed.