Shirong Ge

Friction and wear properties of UHMWPE/Al2O3 ceramic under different lubricating conditions

Abstract Friction and wear behavior of ultra-high molecular weight polyethylene (UHMWPE) sliding against Al 2 O 3 ceramic under dry sliding, and lubrication of fresh plasma, distilled water and physiological saline were investigated with a self-made pin-on-disk apparatus at 37±1°C. The worn surfaces were examined with a scanning electron microscope (SEM). The results show that the friction behavior of UHMWPE is very sensitive to its water absorption state. The wear rate of UHMWPE under dry sliding is the highest and under plasma lubrication is the lowest. The wear mechanisms are different under dry friction and various lubricating conditions.

Research on the fatigue and fracture behavior due to the fretting wear of steel wire in hoisting rope

Hoisting steel rope is an important component of the winding equipment in coalmines. Fretting wear and its induced fatigue and fracture of wires have been the major failure modes of the hoisting ropes. In this paper, a series of experiments on the fretting friction and wear of steel wires were performed on an elastic beam oscillation test rig. The worn wires after fretting tests were put into fatigue test on the servo-fatigue test machine. The research results demonstrated that the fretting wear depth of the steel wires increased with the increasing fretting cycles and contact loads. The fatigue life of the steel wires with fretted damage was inverse proportional to the wear depth, and then to the fretting cycles and contact loads. The fretting wear and fatigue mechanisms were analyzed through SEM morphologies of fretting wear scars and fracture sections. It was found that the wear mechanism of fretting wire depended on the contact loads. For low contact loads, light scratch modes dominated the fretting of wires. When contact loads increased, third body abrasion appeared on the worn surfaces.

Friction and wear behavior of nitrogen ion implanted UHMWPE against ZrO2 ceramic

Abstract As the osteolysis induced by polyethylene wear debris is the main cause of long-term failure of total joint replacements, increasing the wear resistance of ultrahigh molecular weight polyethylene (UHMWPE) will be very important to obtain high quality artificial joint. In this paper, we performed nitrogen ion implantation on UHMWPE with ion doses of 5–125×10 14 /cm 2 . The surface hardness and contact angle on implanted UHMWPE surface were measured. A ball-slid-on-disc tribometer was run, as a comparative test method, to observe the tribological behaviors of ion implanted UHMWPE against ZrO 2 ceramic in dry friction and plasma lubrication. Meanwhile, the profiles of the worn groove on UHMWPE surface were scanned. The experimental results demonstrate that nitrogen ion implantation enhances the microsurface hardness of UHMWPE. The wettability on implanted UHMWPE surfaces is improved. It is found that the friction coefficients of implanted UHMWPE obtain higher values than the untreated one. In plasma lubrication, the friction coefficients of untreated UHMWPE decrease, while the friction coefficients of implanted UHMWPE have little reduction except less fluctuation in wear process. It is shown that the wear rates of nitrogen ion implanted UHMWPE decrease with ion doses in plasma lubrication. In dry friction, however, the wear rates of implanted UHMWPE are 1.8–4.5 times higher than the untreated one. The wear mechanism of untreated UHMWPE is mainly adhesive wear, but the wear mechanism of implanted UHMWPE will shift to abrasive wear and fatigue wear.

Experimental study on the characterization of worn surface topography with characteristic roughness parameter

The fractal dimension and scale coefficient of surface profiles were calculated using the structure function method. Studies show that fractal dimension or scale coefficient is not optimum in characterizing rough surfaces. In consideration of this case, a fractal parameter called the characteristic roughness is put forward by combining the profile fractal dimension and the scale coefficient. Its definition and calculation expression are given. Running-in wear tests were conducted by using a thrustwasher type tester, and surface topographies were measured in the same area of the test specimens at different wear times. Experimental results show that the characteristic roughness parameter is not only more objective but also more sensitive to characterize wear surfaces during the running-in process than fractal dimension or scale coefficient.

The Influence of Normal Load and Sliding Speed on Frictional Properties of Skin

The study of frictional properties of human skin is important for medical research, skin care products and textile exploitation. In order to investigate the influence of normal load and sliding speed on the frictional properties of skin and its possible mechanism, tests were carried out on a multi-specimen friction tester. When the normal load increases from 0.1 N to 0.9 N, normal displacement and the friction coefficient of skin increase. The friction coefficient is dependent on the load, indicating that both adhesion and deformation contribute to the friction behaviour. The deformation friction was interpreted using the plough model of friction. When sliding speed increases from 0.5 mm·s−1 to 4 mm·s−1, the friction coefficient increases and “stick-slip” phenomena increase, indicating that hysteretic friction contributes to the friction. The hysteretic friction was interpreted using schematic of energy translation during the rigid spherical probe sliding on the soft skin surface, which provides an explanation for the influence of the sliding speed on the frictional characteristics of the skin.

Synthesis and Characterization of PVA-HA-Silk Composite Hydrogel by Orthogonal Experiment

PVA-HA-Silk composite hydrogel was synthesized with polyvinyl alcohol (PVA), nano-hydroxyapatite (HA) and natural silk by using the method of repeated freezing and thawing. A series of tests were performed to study water content, stress relaxation behavior, elastic modulus, and creep characteristics of PVA-HA-Silk composite hydrogel. Orthogonal experimental design method was used to analyze the influence degree of PVA, HA and silk (three kinds of raw materials) on mechanical properties and water content of the PVA-HA-Silk composite hydrogel to select the best material ratio according to their overall performance. The results demonstrate that the mass percentage of P VA has the greatest impact on the water content, followed by HA and silk. Compression stress-strain variation of PVA-HA-Silk composite hydrogel presents a nonlinear relationship, which proves that it is a typical viscoelastic material. Comparing the mechanical properties of 16 formulas, the formula of PVA-HA-silk composite hydrogel with mass percentage of PVA 15%, HA 2.0% and silk 1.0% is the best.

Study on Biotribological Behavior of the Combined Joint of CoCrMo and UHMWPE/BHA Composite in a Hip Joint Simulator

UHMWPE composites reinforced with Bovine Bone Hydroxyapatite (BHA) in different contents were prepared by heat pressing formation method. A hip joint wear simulator was used to investigate the biotribological behavior of UHMWPE/BHA composite acetabular cups against CoCrMo alloy femoral heads in bovine synovia lubrication at 37 ±1 °C. It was found that the addition of BHA powder to UHMWPE can improve the hardness and creep modulus of UHMWPE/BHA composites, and decrease their wear rates under bovine synovia lubrication. When the content of BHA filler particles was up to 30 wt%, UHMWPE/BHA composites demonstrated the well design performances of the surface and biotribological properties. Fatigue, ploughing and slight adhesive wear were the main wear mechanisms for UHMWPE and its composites. In addition, the sizes of wear particles became larger with an increase in BHA powder addition. These results suggest that BHA filler is a desirable component to increase the wear resistance of UHMWPE/BHA composites for biomedical applications.

Effect of Preparation Methods on Mechanical Properties of PVA/HA Composite Hydrogel

Poly(vinyl alcohol) (PVA) / hydroxyapatite (HA) composite hydrogel specimens were prepared with 15% PVA and 1%, 2%, 3%, 4% and 5% HA by repeated freezing-thawing. The tests of static and dynamic mechanical properties were carried out to discuss the influence of different contents of HA and freezing-thawing cycles on the mechanical properties of PVA/HA composite hydrogel. The results of static mechanical tests showed that the PVA/HA composite hydrogel with 3% HA and nine freezing-thawing cycles had excellent stress relaxation properties, higher relaxation ratio, lower stress equilibrium value and presented better properties of creep and recovery. The results of dynamic mechanical test showed that the PVA/HA composite hydrogel with nine freezing-thawing cycles had higher storage modulus and loss modulus, so was the PVA/HA composite hydrogel with 3% HA.

Microstructure and tribological properties of complex nitrocarburized steel

Abstract Two kinds of tribological apparatus were employed to investigate the friction and wear performance of steel 1045 treated by quenching plus tempering and complex nitrocarburizing processes. The microstructures, phase identification, surface hardness and hardness profiles of the specimens were analyzed by optical metallography, microhardness tests and X-ray diffraction; at the same time the surface roughness of specimen surfaces was tested using a profilometer. The experimental results show that: the e-phase formed on the specimen surface has a significant effect on reducing the friction coefficient and improving wear resistance; the oxidation after nitrocarburizing rarely changes the friction coefficient but decreases the wear resistance; and with oxidation plus polishing and secondary oxidation complex treatments being performed, the wear resistance of nitrocarburized specimens is improved even further.

Microstructure and tribological behaviour of nitrocarburizing-quenching duplex treated steel

This paper explores salt bath nitrocarburizing and nitrocarburizing-quenching duplex treatment technologies. For comparison, a quenching-tempering treatment was also conducted. By means of metallographic examination, microhardness tests and X-ray diffraction analysis, the microstructures, phase structures, surface hardnesses and hardness profiles of 1045 steel treated by several techniques were investigated. The ball-on-block and ring-on-block apparatuses were employed to investigate the friction coefficient and wear-resistance respectively. The surface roughness was also measured by a profilometer. The experimental results indicate that a higher sub-surface hardness and a superior hardness profile are obtained by nitrocarburizing-quenching duplex process. This in turn improves the wear-resistance and fatigue strength, although the surface hardness is somewhat lower compared with that obtained by nitrocarburizing. It also demonstrates that the e-phase formed on the steel surface has significant effects on reducing friction and improving wear-resistance. X-ray diffraction analysis shows that the phases at the nitrocarburized specimen surface are mainly e-compound [Fe3(N,C)] and small amounts of Fe4N(γ′) and Fe2–3(N,C). While the phases at the nitrocarburized-quenched specimen surface are very different from those at the nitrocarburized specimen. In this case, the e-compound has decomposed almost completely and the nitrogen and carbon diffuse to the γ-Fe at the temperature of quenching to form the supersaturated solid solution which will become martensite containing nitrogen and carbon along with retained austenite after subsequent water cooling.