Micromechanics Characterization on the Lower Bound Young’s Moduli of Composite Materials Measured from Nanoindentation

The measurements of the through-thickness Young’s moduli of composite materials are important, but they were not systematically reported because of the complexity. In this paper, a lower bound characterization approach for the Young’s moduli using nanoindentation is proposed based on contact mechanics and micromechanics analysis. This approach was applied to grid nanoindentation of a glass-fiber composite material system, and the estimated lower bound was around 40% lower than the directly measured Young’s modulus of the same composite system using Hertz’s contact law. Therefore, the proposed approach provides a conservative measurement if the actual through-thickness Young’s modulus is not available. This approach is helpful for nanoindentation users without comprehensive knowledge of micromechanics and contact mechanics to conduct complicated nanoindentation experiments for composite materials.