| 초록 |
The elastic modulus of materials at small scales has been measured by nanoindentation in which penetration force and depth are measured continuously. The initial unloading stiffness of polymer materials is generally dependent on the unloading rate of nanoindentation, so it is not easily measured by nanoindentation. At high unloading rates, however, the viscoelastic effect can become negligible. The values of elastic modulus for PVC, POM, and PTFE were derived from a convergent stiffness value at the high unloading rate; these modulus values are defined as an invariant property and are compared to convergent values of elastic modulus measured by tensile testing at high loading rates. The ratios of the two modulus values, which ranged from 1.03 to 1.20, were taken as correction factors between nanoindentation and tensile testing. Using these correction factors makes it possible to determine the true contact area and hardness. |
