Optical indentation microscopy – a new family of instrumented indentation testing

Abstract

A novel test system/analysis is proposed for determining the in situ true contact area during indentation loading/unloading by the use of an optically transparent indenter. A sapphire planoconvex lens as a spherical indenter or a diamond tetrahedral pyramid indenter is optically coupled with a microscope system equipped with a CCD video camera. This indentation microscope enables us to directly view the in situ contact impression, along with the measurement of the hysteresis curve of the indentation load-penetration depth relation. The in situ contact area can be readily determined from each frame of the video movie using an image analyzer that is synchronized with the indentation load. Accordingly, the mechanical properties including the true indentation stress–strain curve can be evaluated directly from these observable parameters without using any assumptions that have always been required for estimating the contact area in the conventional depth-sensing indentation apparatus.