Digital image correlation (DIC) measurement of contact stiffness

Measurements with digital image correlation of normal and tangential contact stiffness for ground Ti-6Al-4V interfaces suggest a linear relationship between normal contact stiffness and normal load and a linear relationship between tangential contact stiffness and tangential load. The normal contact stiffness for these surfaces is observed approximately to be inversely proportional to an equivalent surface roughness parameter, defined for two surfaces in contact. The ratio of the tangential contact stiffness to the normal contact stiffness at beginning of a load step is seen to be given approximately by the Mindlin ratio. A simple empirical model is proposed to estimate both normal and tangential contact stiffness at different loads for ground Ti-6Al-4V surfaces of known surface roughness and coefficient of friction.

Methods
Experimental images and load data were analysed with Digital Image Correlation using DaVis StrainMaster software. This was post-processed with MATLAB.