Experimental determination of the non-linear, large strain zonal mechanical properties of cartilage for use in quasi-static finite element model

by Mageswaran, Prasath.

Prasath Mageswaran. Experimental determination of the non-linear, large strain zonal mechanical properties of cartilage for use in quasi-static finite element model. (Under the direction of Dr. P. L. Mente) A series of impact tests on porcine cartilage are being conducted to investigate the mechanism of tissue degeneration. In order to investigate the stress distribution over the impact area of the tissue and to correlate that with the available physical data, an Ogden hyperelastic constitutive model for porcine articular cartilage was determined. The Ogden model was determined for surface, mid and deep zones of cartilage. The model will be used as an input for a finite element model for an impact test on cartilage. The inhomogeneous nature of cartilage was also investigated in this study. Tensile and compressive properties of porcine articular cartilage were determined by carrying out uniaxial tensile and compression tests at a high rate of loading. The tests were carried out on 120 – 160 µm thick specimens from the surface, mid and deep zones of cartilage. Specimens tested in tension, were obtained from orientations that are parallel to the split-line direction. Deformation measurement for the tensile test was obtained using a high speed camera set at 250 fps. The nonlinear tensile stress-strain relationship of the cartilage specimens from the three zones was approximated mathematically using Fung’s exponential equation. It was found that the Fung’s model did not provide an adequate fit to the stress-strain relationship of mid and deep zone specimens when compared to that of the surface zone. The Young’s modulus for tension and compression was determined from the uniaxial tests. The study found that both tensile and compressive stiffness of cartilage varied with depth. There was a high degree of tension-compression nonlinearity.