Assessment of physical, chemical, and tribochemical properties of biomedical alloys used in explanted modular hip prostheses

During their service life, modular interfaces experience tribological, and corrosion phenomena that lead to deterioration, which in turn can cause a revision procedure to remove the failed prosthesis. To achieve a clearer understanding of the surface performance of those biomedical alloys and the role of the surface properties in the mechanical and chemical performance, samples were taken from retrieval implants made of Ti6Al4V and Co28Cr6Mo alloys. Polarization resistance and pin-on-disk tests were performed on these samples. Physical properties such as contact angle, roughness, microhardness, and Young’s modulus were determined. A correlation between surface energy and evolution of the tribological contact was observed for both biomedical alloys. In tribocorrosion tests, titanium particles seem to remain in the surface, unlike what is observed in CoCr alloys. These metallic or oxidized particles could cause necrosis or adverse tissue reactions.

Wälzfestigkeit erodierter Oberflächen im Zwei-Scheiben-Zahnradanalogieversuch

Due to advances in power electronics and high-frequency process control, the technology of electrical discharge machining (EDM) has received a decisive technological boost in the last two decades to increase the achievable removal and cutting rates and to minimize the thermally influenced surface zone. At the same time, wire electrical discharge machining in particular has always been characterized by high achievable geometrical accuracy. In addition, a cup-shaped surface structure is formed in EDM as a result of the individual discharge points, which can offer targeted optimization potential with regard to tribological properties in rolling-sliding contacts. For this reason, the objective of this report is the knowledge of the contact fatigue strength of eroded surfaces in comparison to a ground reference with a focus on tribological contact conditions typical for gears.

Calculation of the actuator system in swash plate axial piston machines by a coupled multibody and TEHL simulation

This paper presents a method for coupling a multibody simulation for the actuator system in axial piston machines in combination with a transient, three-dimensional, thermal elastohydrodynamic contact calculation. For the tribological investigation, the oscillating piston/cylinder contact is focused, whereby a simplified model of the actuator system simulates the loads. The developed method allows the integration of a complex tribological contact simulation under mixed friction conditions into a dynamic multibody simulation based on the Newton–Euler method. It is discussed how the accuracy of the results and the calculation time can be improved by the procedure.

Effect of Various Type of Nanoparticles on Mechanical and Tribological Properties of Wear-Resistant PEEK + PTFE-Based Composites

The mechanical and tribological properties of polyetheretherketone (PEEK)- and PEEK + PTFE (polytetrafluoroethylene)-based composites loaded with and four types of nanoparticles (carbonaceous, metallic, bimetal oxide, and ceramic) under metal- and ceramic-polymer tribological contact conditions were investigated. It was found that loading with the nanofillers in a small content (0.3 wt.%) enabled improvement of the elastic modulus of the PEEK-based composites by 10–15%. In the metal–polymer tribological contact, wear resistance of all nanocomposites was increased by 1.5–2.3 times. In the ceramic-polymer tribological contact, loading PEEK with metal nanoparticles caused the intensification of oxidation processes, the microabrasive counterpart wear, and a multiple increase in the wear rate of the composites. The three component “PEEK/10PTFE/0.3 nanofillers” composites provided an increase in wear resistance, up to 22 times, for the metal–polymer tribological contact and up to 12 times for the ceramic-polymer one (with a slight decrease in the mechanical properties) compared to that of neat PEEK. In all cases, this was achieved by the polymer transfer film formation and adherence on the counterparts. The various effects of the four types of nanoparticles on wear resistance were determined by their ability to fix the PTFE-containing transfer film on the counterpart surfaces.

Cellulose Pulp- and Castor Oil-Based Polyurethanes for Lubricating Applications: Influence of Streptomyces Action on Barley and Wheat Straws

The replacement of mineral oils and non-renewable gelling agents is an imperative requirement for the lubricant industry in the near future. In this framework, cellulose pulp and castor oil are proposed as sustainable substitutes for these components. Biological treatment has been explored and evaluated to enhance the dispersing and thickening properties of cellulose pulp in oil media. Streptomyces sp. MDG147 and MDG301 strains were employed to modify agricultural wheat and barley straw residues from which cellulose pulp was obtained afterwards. In addition, an environmentally friendly process for the production of cellulose-pulp-/castor-oil-based polyurethanes was applied, in which neither catalysts nor harmful solvents were used, resulting in chemical oleogels. These oleogels were rheologically and tribologically characterized to evaluate their performance as lubricating greases. The enzymatic activity pattern developed was dependent on the raw material, the strain type, and the temperature, influencing the cellulose pulp’s composition, polymerization degree, and crystallinity. These modified characteristics tuned the rheological behavior of the different oleogels, providing a beneficial range of viscoelastic responses and viscosity values that were generally favored by the Streptomyces action. Furthermore, the friction coefficient and dimensions of wear scars measured in a tribological contact were comparable to, or even lower than, those found with commercial and other bio-based lubricating greases that have previously been studied.

New Design Concepts for the Tribological Contact of Cylinder Block and Valve Plate

Axial piston machines are the most widely used type of hydraulic displacement machines and are characterized by their high reliability and efficiency. However, in order to ensure the high efficiency, the tribological contacts have to be precisely optimized. One of the three essential contacts in axial piston machines is the contact of valve plate and cylinder block, which is the subject of this paper. In a previous research project, a simulation model was built up specifically for the tribological contact of valve plate and cylinder block. A test rig was developed and installed for the validation of the simulation results. Both, the experimental and the simulation results show that the cylinder block tilts to the high-pressure side. It holds this preferred position nearly constantly for the different load situations over one revolution with four or five pistons pressurized with high pressure at the same time. The tilting increases the danger of solid body contact in the area of minimum gap height. In addition, it leads to temperature hot spots. Both effects necessitate the use of coatings as alternatives to the commonly used leaded alloys. This paper presents new design concepts for the optimization of the tribological contact of valve plate and cylinder block. Additional pressure pockets in the valve plate’s high-pressure kidney generate a torque and thus reduce the tilt angle of the cylinder block. By implementing additional pressure pockets at the cylinder block an imbalance results, which prevents a constant preferred position. Both concepts have the aim to reduce the heat concentration and improving the overall behavior of the tribological contact. The development and comparison of these concepts are based on a numerical analysis.

Tribological Investigation on the Friction and Wear Behaviors of Biogenic Lubricating Greases in Steel–Steel Contact

The applications of biogenic lubricating greases to machine elements play important roles in the reduction of friction energy and minimizing wear in a tribological contact, as well as the prevention of environmental pollution. The aim of this work was to investigate completely biogenic lubricating greases from a tribological point of view. Model greases were examined using a ball on a disc tribometer at a constant normal force to investigate the friction and wear process according to Fleischer’s energetic wear model. Using the energy-based wear model, the friction and wear process could be interpreted as a cause–effect sequence. Moreover, the influence of the model grease composition on the friction and wear process was analyzed. In addition, rolling bearing tests were performed to investigate the tribological behaviors of some selected biogenic greases during real machine element contact. These tests allowed for the quantification of the friction torque behavior of the full bearing and the evaluation of the wear obtained through lubricant analysis procedures. This experimental work provides useful information regarding the influence that the composition of biogenic model greases has on friction and wear behaviors in a tribological contact.