Depth-dependent normal strain of articular cartilage under sliding load by the optimized digital image correlation technique

Abstract

The sliding experiments of articular cartilage were conducted by applying an optimized digital image correlation (DIC) technique and the depth-dependent normal strain and friction force were analyzed for cartilage. It is found that the friction forces of cartilage increase firstly and then decrease slowly with the slide of slider and increase with increasing compressive strain. The normal strain values of different layers increase obviously with sliding time with compressive strain of 35.2%. The normal strain values of superficial layer and middle layer appear in an increasing trend however little change of normal strain in deep layer is observed with sliding time with compressive strains of 18.9% and 11.2%. The depth-dependent normal strain values decrease along depth direction with constant compressive strain and the normal strain values of different normalized depth increase with increasing compressive strain. The friction forces and depth-dependent normal strain values of cartilage decrease slightly with increasing sliding rates. It is noted that the first sliding friction forces are the largest and then the friction forces decrease with increasing sliding numbers. The normal strain value increases with increasing sliding numbers and the increasing amplitude of normal strain during the former two sliding is significant. The fitting relationship of normal strain and normalized depth was obtained considering the effects of compressive strain and sliding rate and the fitting curves agree with the experimental data for cartilage with different compressive levels and sliding rates very well.