On the Dependence of Rheology of Hyaluronic Acid Solutions and Frictional Behavior of Articular Cartilage

Hyaluronic acid (HA) injections represent one of the most common methods for the treatment of osteoarthritis. However, the clinical results of this method are unambiguous mainly because the mechanism of action has not been clearly clarified yet. Viscosupplementation consists, inter alia, of the improvement of synovial fluid rheological properties by injected solution. The present paper deals with the effect of HA molecular weight on the rheological properties of its solutions and also on friction in the articular cartilage model. Viscosity and viscoelastic properties of HA solutions were analyzed with a rotational rheometer in a cone–plate and plate–plate configuration. In total, four HA solutions with molecular weights between 77 kDa and 2010 kDa were tested. The frictional measurements were realized on a commercial tribometer Bruker UMT TriboLab, while the coefficient of friction (CoF) dependency on time was measured. The contact couple consisted of the articular cartilage pin and the plate made from optical glass. The contact was fully flooded with tested HA solutions. Results showed a strong dependency between HA molecular weight and its rheological properties. However, no clear dependence between HA molecular weight and CoF was revealed from the frictional measurements. This study presents new insight into the dependence between rheological and frictional behavior of the articular cartilage, while such an extensive investigation has not been presented before.

Effect of Contact Characteristics on the Friction and Wear Behaviors of Stainless Steel/Copper-Impregnated Metalized Carbon under Electric Current

Influence of the support stiffness and contact force on friction and wear behaviors of stainless steel rubbing against copper-impregnated metalized carbon under electric current was researched on an improved friction and wear test machine. The result indicates that the support stiffness and the contact force significantly affect the friction coefficient of contact pairs, wear and surface roughness of pin samples. The appropriated support stiffness and contact force can effectively reduce friction material wear of contact couple.

The Influence of the Temperature in Severe Wear of Copper Contact Wire/carbon Strip under Electric Current

A series of experimental tests were carried out using copper contact wire rubbing against carbon strip under electric current on a pin-on-disc test. The aim to experiment can be understand the roles of the thermal wear in severe wear of copper/carbon strip under electrical current passage. During testing, the contact temperature and friction coefficient were recorded. The wear volumes of carbon strip specimens were measured. The results indicate that the temperature rise of contact couple with and without electric current is distinctly different. And the friction coefficient increases firstly due to the accumulation of wear debris, and then decreases with the increasing of electric current due to the accumulation of electric heat and friction heat on contact interface. It can be found that the wear volumes of carbon strip samples with electric current are larger than those without electrical current. Several thermal wear tests were conducted to study the influence of the temperature on the wear of carbon strip samples. The result indicates that thermal wear, oxidation wear and abrasive wear are a main mechanism for the severe wear of carbon strip samples.

Effect of Arc Discharge on Friction and Wear Behaviors of Stainless Steel/Copper-Impregnated Metalized Carbon Couple under Electric Current

Friction and wear tests of stainless steel rubbing against copper-impregnated metalized carbon with electric current were carried on the pin-on-disc tester. The result indicates that arc discharge occurs in the process of experiments, and the intensity of arc discharge of interface increases with increasing of electric current and sliding velocity. As increasing of the arc discharge intensity, friction coefficient shows a tendency of slightly increase. While the rate of copper-impregnated metalized carbon material increase significantly with the increase of arc discharge intensity. Through observing the worn surface morphology of pin samples, it is found that the abrasive wear is dominant at small arc discharge due to worn particles and arc ablation craters, but arc erosion and oxidation wear are the main wear mechanisms in condition of large arc discharge due to arc discharge and its producing high temperature. The materials transfer of contact couple occurs in the process of friction and wear.