Nanoindentation for testing material properties

Abstract

Nanoindentation has seen widespread applications for characterizing the mechanical properties of materials. The technique involves the measurement of applied load and penetration depth, at very small scales, when the indenter is pressed against the test material. An indentation test requires minimal material preparation, and can be performed multiple times on a single specimen. It is particularly suited for thin films, coatings and modified surfaces, as well as materials in their bulk form. Rooted in classical contact mechanics, theories and practice of nanoindentation testing have been developed to extract a wide array of material properties. This chapter presents a comprehensive overview of the fundamentals of nanoindentation. Background information about the indentation theories is first reviewed, with emphasis on the relevant Hertzian contact analysis and Sneddon’s solutions. Common indenter types are then presented, which is followed by discussion on the two most frequently measured properties, hardness and elastic modulus. Guidelines and best practices for the determination of contact stiffness and contact area, along with corrections of thermal drift and machine compliance, are discussed. Representative indentation methodologies for characterizing residual stresses, time-dependent deformation for metals and polymers, fracture toughness for brittle materials, and adhesion of coatings on substrates are also included in the presentation. Computational modeling is shown to yield valuable information of internal deformation field which can be correlated with the indentation response. Unique indentation features and uncertainties associated with material heterogeneity, as well as remaining challenges and future directions, are also discussed.