Study On Friction Behavior About Natural Articular Cartialge

In this paper, on the investigative object of the bovine knee articular cartilage, mass distribution of absorption fluid and permeability of natural cartilage were measured, cartilage surface and inner structure were observed, deformation characteristics of different loading pattern were investigated, frictional behavior of sliding and swing pattern were discussed, and fluid characteristics of cartilage interface were simulated. These results are of great importance in understanding the carrying capacity and movement mechanism of natural joints, comprehending biotribological mechanism of natural frictional pairs and developing better artificial cartilages.Friction sliding behaviors of cartilage-on-glass and cartilage-on-cartilage layer were investigated. These results showed that higher cartilage deformation helped to improve the contact probability between solid phases of cartilage configurations, which made the coefficient of friction increased with time as a whole. Biphasic Characteristics of natural cartilage led to the following phenomenon. Coefficient of friction from cartilage-on-cartilage layer was significantly lower than that from cartilage-on-glass pairs.Absorption fluid distribution and cartilage permeability were measured. It was found that mass percent of cartilage absorption fluid had a wavily descending relation with the depth from 94.4 percent of the outer zone to 78.1 percent of the deepest zone. Pressure difference functioned with a negative correlated with cartilage permeability, and its value was about 6.482×10-16m4N-1s-1. Micro-max morphology instrument was employed to observe the surface morphology and inner structure about cartilage samples. These results indicated that natural cartilage had irregular surface and micro structure, and the difference between the adjacent peaks and troughs was about 0.05~1.83μm. Micro-pore distribution, sizes and shapes all had fractal properties with its box-counting dimension about 1.737. Based on the Sierpinski fractal patterns, the schematics of micro-pore structures were reconstructed about superficial layer, middle layer, deep layer and cross-section layer.From the cartilage deformation curves about linear and alternating loads, elastic modulus of linear loads underwent through an initially sharp decline and afterwards slow increase with the strain, and elastic modulus of fast load was higher than that of slow load. The indentation deformation produced by alternating loads was obviously higher than that by constant load, and load magnitude played a less role on the ratio of alternating load to deformation and phase difference of deformation lagging load. The ration and phase difference was about 9.1 and 0.25, respectively. Based on the contact pairs of cartilage-on-cartilage, cartilage-on-glass, and ball-on-cartilage, friction behavior in the reciprocating sliding was investigated. These results showed geometric characteristics of surface outlines played an important role on contact state and friction behavior from the cartilage configurations. And exterior load, sliding velocity, preloading time, contact area and lubricated fluid only led to secondary influences. Friction properties of cartilage-on-cartilage swing demonstrated that larger swing offset produced higher wavy magnitude of contact load, and lower swing velocity brought larger cartilage deformation. Coefficient of friction of inner swing was evidently higher than that of outer swing, and its magnitude of inner swing was lower than that of outer swing. Correlative coefficient of swing testing was evidently higher than that of sliding testing,which showed that contact characteristic of cartilage friction configurations in the swing testing was in better state.From the simulation about cartilage friction configurations, it was found that fluid flow characteristics on the cartilage surface were related with contact frequency and contact pairs. Contact stress, pore pressure, fluid velocity and contact displacement all functioned as a nonlinear relation with time. When cartilage surface was involved in contact area, corresponding contact stress and pore pressure presented a stale variation, but fluid velocity and contact displacement were both influenced by contact pairs. When contact surface was in the interval contact, corresponding contact stress and pore pressure went through an obvious variation in the vicinity of contact area, and decreased to zero in the other regions, but fluid velocity and contact displacement in the vertical direction were both higher than that in the horizontal direction.