No abstract

Surface roughening, with certain roughness topography, is thought to be as an effective tribological method of decreasing friction coefficient of kinematic pairs. Friction and wear of AISI1045 steel surface roughened by convenient and economical way of sandblasting was investigated under lubrication conditions. Roughened and polished samples run against Φ4mm GCr15 pin lubricated by engine oil were tested in reciprocating mode with different load and speed on UMT- testing machine. It is found that there exists the optima surface roughness (Ra is about 3.92μm) roughened by sandblasting in which the least wettability contact angle between engine oil and textured steel surface is obtained, hence the lowest friction coefficient and wear rate is due to the optima hydrodynamic sliding property, although the sliding surface was not in hydrodynamic lubrication state.

Nitrogen ion implantation and carburization technology were chosen to modify the surface properties of titanium alloys. The surface components and element concentration distribution profile of the modified titanium alloy were characterized with X-ray photoelectron spectroscopy (XPS). The surface hardness and contact angle of the modified titanium alloys were measured to analyse the improvement of the mechanical properties and wettability. Friction and wear tests were performed between the modified titanium alloy plate against a ZrO 2 ball on a universal multi-functional tester . Then the tribological behaviours of the modified titanium alloys were investigated by means of scanning electron microscopy and a laser granularity analyser. The XPS analysis results indicated that titanium nitride and titanium carbide were formed on the titanium alloy surface. In addition, the surface hardness of nitrogen-ion-implanted titanium increased from 335 ± 7.4 HV (n = 6) to 357 ± 9.8 HV (n = 6), whereas the surface hardness of carburized titanium increased to 750 ± 25.3 HV (n = 6). The contact angles of nitrogen-ionimplanted and carburized titanium alloys were decreased from 83 to 80 and 71.5 • , respectively, indicating an improvement of surface wettability. In addition, the wear results indicated that both nitrogen ion implantation and carburization greatly improved the wear resistance of the titanium alloys and decreased the size of the wear debris. Finally, an attempt was made to explain the wear mechanisms of the modified titanium alloys.

Ultra-high molecular-weight polyethylene (UHMWPE) has been used in total hip replacement for the last three decades. Despite the advancements in prosthesis design, the wear of UHMWPE remains a serious clinical problem; the release of wear debris may induce osteolysis and implant loosening. Understanding of wear behavior and wear debris morphology of the polyethylene is essential to improve the reliability of hip joint implants. The investigation in this paper carried out wear simulation tests of UHMWPE on Al2O3, 316L stainless steel, CoCrMo alloy and Ti6Al4V alloy, respectively. The lubrication of plasma solution and bovine serum solution was presented in wear tests. The effect of motion and loading on the wear behavior and wear debris morphology, and the influence of femoral head material and assembly style were studied in order to obtain a better understanding of the morphology of ultra-high molecular weight polyethylene wear particles. It is shown that the wear of UHMWPE acetabular cups against metal femoral heads was significantly higher than that against ceramic heads. The presence of protein in lubricant increases the wear of UHMWPE acetabular cups on Al2O3 heads. The wear rates of UHMWPE in multi-directional motion are approximately 2.5 times of those in uni-directional motion. The size distribution range of the UHMWPE debris particles for all head materials varies from submicron particles up to several hundreds micron. The size distribution range of wear debris particles is not directly related to wear resistance of UHMWPE, but significantly influenced by wear mechanisms. The UHMWPE debris particles produced in hip wear simulation tests are classified as round debris, flake-like debris and stick debris, which are closely related to the primary mechanisms of abrasive wear, adhesive wear and fatigue wear.

In order to investigate the maximum stairs-climbing capability of the six-track robot with four swing arms and the centroid position control in the climbing process, firstly, the isolated steps and successive stairs in reality environments were simplified into a model that composed of horizontal planes and vertical planes; afterward, the robots centroid distribution was analyzed, the step-climbing methods and processes were given, and the relation equations of the step height, the arms swing angles and the main track evaluation angle were founded; Lastly, the conditions of the maximum step height and the conditions of climbing successive stairs using the slope-climbing method was deduced. Using the parameters of CUMT-III type coal mine exploring robot prototype, the relation curves of the step height and the robot elevation angle was drawn when the rear swing arms spread, and the 3D relation graphs of the robot elevation angle, rear arms swing angles and the step height were drawn, when the swing arms took some specific swing angles. The maximum theoretical step height of the prototype were obtained, which were compared with the test results in laboratory. This paper will provide theoretical basis for centroid position control in steps and stairs climbing process.