Polymeric Composite Materials of Tribotechnical Purpose with a High Level of Physical, Mechanical and Thermal Properties

Polymeric composites (PC) of tribological applications with a high level of physical, mechanical and thermal properties based on aromatic polyamide and silica gel have been developed. Regularities have been obtained that describe the effect of the filler content in PC on the friction coefficient, temperature on the friction surface and the intensity of linear wear rate of the studied PC-steel friction pair. It was found that the optimal silica gel content in the polymer matrix is 10 wt %. The morphology of the steel surface of friction after friction interaction with PC based on aromatic polyamide and silica gel was studied. The formation of an antifriction film on the steel surface of friction was discovered, which contributes to a decrease in the friction coefficient, temperature on the friction surface, and the linear wear intensity of the studied PC. The influence of the load and sliding speed on the main tribotechnical characteristics of the PC-steel friction pair has been studied. Mathematical laws were derived that describe the influence of the main external factors (load and sliding speed) on the friction coefficient and intensity of linear wear rate of the studied friction pair. Physical, mechanical and thermal investigations of the developed PC were carried out and it was found that the introduction of 10 wt % silica gel contributes to their 5–10 % increase.

Increasing the resource of agricultural machines

The object of research is the technological process of increasing the service life of pointed cultivator shares of tillage machines through the use of a progressive method of vibration hardening. One of the most problematic areas is the inadequate study of the investigated technological process of restoring the working bodies of agricultural machines. In order to gain a deeper understanding of the process of vibration processing of the material of these machine parts during their restoration, it is necessary to conduct further experimental studies. In the course of the study, it has been found that the use of vibration deformation of the surface layer of the material of parts contributes to an increase in their resource. The optimal parameters of vibration hardening of the cutting elements of the cultivator shares of tillage machines have been determined, which makes it possible to increase their durability. The main parameters of vibration hardening are revealed: the vibration amplitude of the processing tool is 0.75 mm; vibration frequency – 1400 min–1; hardening time – 30 s. As a research result, the assessment of the change in linear wear along the width of the cutting element of the cultivator duckfoot of tillage machines was carried out. In cultivators with tines restored by welding angle plates made of 45 steel (GOST 1050-2013, GB 699-88), sormite surfacing and vibration hardening, the linear wear rate by weight of cutting elements is 35–43 % less than in new tines. A study of changes in the wear of the cutting edge of cultivator shares was carried out, which, when restored by welding corner plates made of steel 45 (GOST 1050-2013, GB 699-88), surfacing with sormite and vibration hardening, is 1.57–1.68 times less than in new shares. In comparison with existing technologies, the developed technology provides a reduction in the wear of cutting elements by 10–17 %, in comparison with new ones made of 65G steel (GOST 14959-2016, GB 1222). The coefficient of technical utilization of the cultivator with tines restored according to the developed technology, in comparison with the new ones, is 1.07 times higher.

Tribology of Polymer Blends PBT + PTFE

This paper presents results on tribological characteristics for polymer blends made of polybutylene terephthalate (PBT) and polytetrafluoroethylene (PTFE). This blend is relatively new in research as PBT has restricted processability because of its processing temperature near the degradation one. Tests were done block-on-ring tribotester, in dry regime, the variables being the PTFE concentration (0%, 5%, 10% and 15% wt) and the sliding regime parameters (load: 1, 2.5 and 5 N, the sliding speed: 0.25, 0.5 and 0.75 m/s, and the sliding distance: 2500, 5000 and 7500 m). Results are encouraging as PBT as neat polymer has very good tribological characteristics in terms of friction coefficient and wear rate. SEM investigation reveals a quite uniform dispersion of PTFE drops in the PBT matrix. Either considered a composite or a blend, the mixture PBT + 15% PTFE exhibits a very good tribological behavior, the resulting material gathering both stable and low friction coefficient and a linear wear rate lower than each component when tested under the same conditions.

Tribological Behavior of Polymers and Polymer Composites

This chapter means to explain the tribological behavior of polymer-based materials, to support a beneficial introducing of those materials in actual applications based on test campaigns and their results. Generally, the designers have to take into consideration a set of tribological parameters, not only one, including friction coefficient, wear, temperature in contact, contact durability related to application. Adding materials in polymers could improve especially wear with more than one order of magnitude, but when harder fillers are added (as glass beads, short fibers, minerals) the friction coefficient is slightly increased as compared to neat polymer. In this chapter, there are presented several research studies done by the authors, from which there is point out the importance of composite formulation based on experimental results. For instance, for PBT sliding on steel there was obtained a friction coefficient between 0.15 and 0.3, but for the composite with PBT + micro glass beads, the value of friction coefficient was greater. Adding a polymer playing the role of a solid lubricant (PTFE) in these composites and also only in PBT, decreased the friction coefficient till a maximum value of 0.25. The wear parameter, linear wear rate of the block (from block-on-ring tester) was reduced from 4.5 μm/(N⋅km) till bellow 1 μm/(N⋅km) for a dry sliding regime of 2.5…5 N, for all tested sliding velocities, for the composite PBT + 10% glass beads +10% PTFE, the most promising composite from this family of materials. This study emphasis the importance of polymer composite recipe and the test parameters. Also there are presented failure mechanisms within the tribolayer of polymer-based materials and their counterparts.

Long-term performance of oxidized zirconium on conventional and highly cross-linked polyethylene in total hip arthroplasty

Introduction: Polyethylene wear and subsequent osteolysis remain obstacles to the long-term survivorship of total hip arthroplasty (THA). Highly cross-linked polyethylene (XLPE) with radical quenching represents a massive leap forward with dramatically improved wear rates compared to ultra-high molecular weight polyethylene (UHMWPE). In this study we evaluate the wear of UHMWPE and XLPE coupled with oxidized zirconium (OxZr) femoral heads. Methods: A longitudinal, retrospective analysis was performed identifying consecutive patients who received a 28-mm OxZr-on-polyethylene primary THA from 2003 to 2004 by a single, high-volume arthroplasty surgeon. Patients were divided into two groups: those that received (1) UHMWPE liner and (2) a highly XLPE liner. Patients were included if clinical follow-up was complete to 2014 or later. Radiographic analysis was performed by two blinded observers. Measures included cup position, annual linear wear rate, and presence of osteolysis. Pairwise comparisons, correlations, and inter-rater reliability were calculated. Results: Eighty patients were in the UHMWPE group with an average follow-up of 10 ± 1.23 years and 88 patients in the XLPE group with an average of 10 ± 1.03-year follow-up. Average age (68) was similar between groups (p = 0.288). Observer reliability was excellent for cup abduction (ICC = 0.940), anteversion (ICC = 0.942), and detection of osteolysis (ICC = 0.811). Annual linear wear rates were significantly higher (p = 1 × 10−19) with UHMWPE (0.21 ± 0.12 mm/year) compared to XLPE (0.05 ± 0.03 mm/year). Linear wear rate was significantly correlated to decreasing acetabular abduction (p = 0.035). Osteolysis was noted only in the UHMWPE group, with 17 patients (21.2%) exhibiting acetabular osteolysis and 37 (46.3%) patients exhibiting femoral osteolysis. Conclusions: OxZr coupled with XLPE showed minimal wear and no osteolysis at 10-year follow up. The yearly linear penetration rate is similar to that seen in other studies of XLPE THA. A careful longitudinal follow-up will be required to determine if advanced bearings such as OxZr or ceramic can show improved performance in the second decade of implantation.

A Model of Cylindrical Gear Failures Using the Criterion of the Working Surface Wear Resistance

Cylindrical gear failure due to tooth wear is one of the most common reasons for the decreased technical and economic indicators of various units resulting from the forced downtime for gear replacement or repair. Nowadays, the linear wear rate, an indicator that is found experimentally, is used to determine gear service life based on the statistical linear dependence of the wear on the friction forces. The determination of this indicator requires a large amount of data on the wear obtained with real transmissions or relevant laboratory samples that increases time and financial costs. Therefore, an analytical model of wear failures has been developed for project estimation of gear service life and the search for effective and lasting design solutions. The model represents a system of constitutive equations, which includes an energy equation describing the change in the current state of a pair of wear gear wheels and the conditions for their transition to the limiting state, a basic kinetic dependence of the energy-mechanical theory of stationary tribocoupling wear, and an equation for determining the transmission’s expected service life. The simultaneous solution of this system of equations taking into account the dependencies that describe the initial and boundary conditions of the gear element interaction resulted in the formulation of the algorithm for calculating their average expected service life. This allowed the authors to perform a comparative analysis of the effectiveness of various design options for improving gear durability and select the most appropriate ones. A distinctive feature of the proposed calculation algorithm is that it does not involve searching for experimental parameters similar to the linear wear rate.

Higher offset cross-linked polyethylene acetabular liners: is wear a significant clinical concern?

Introduction:Total hip arthroplasty (THA) is the 2nd most common total joint replacement surgery in the United States. However, not all THA devices perform well and need revised for several reasons including dislocation. Higher offset acetabular liners reduce this problem by creating a more anatomically/biomechanically natural hip joint, increasing soft-tissue tension, and accommodating larger femoral heads in smaller acetabular cups via increased polyethylene thickness. To our knowledge, however, in vivo wear (another failure mode) performance of offset acetabular liners remains unknown.Methods:2 cohorts of 40 individuals (0-mm, 4-mm offset acetabular liners, respectively) from a single surgeon’s consecutive caseload were assessed. 6-week/5-year post-op radiographs were compared using a validated method using SolidWorks software to assess in vivo linear and volumetric wear rates. Resultant surgical offset was also quantified using this method.Results:Linear wear rate for 0-mm and 4-mm offset cohorts were 0.01 ± 0.09 mm/year and 0.08 ± 0.12 mm/year, respectively. Volumetric wear rate for 0-mm and 4-mm offset cohorts were 30.4 ± 20.4 mm3/year and 61.6 ± 42.1 mm3/year, respectively. Both of these were statistically significant. Neither linear nor volumetric wear rate was correlated with resultant surgical offset.Discussion:To our knowledge, this is the 1st study to compare in vivo wear performance of 0-mm and 4-mm offset acetabular liners. Although linear and volumetric wear rates were different between cohorts, neither reached previously established osteolysis thresholds. Moreover, wear rates were not correlated with resultant surgical offset. Finally, no patients in either cohort showed signs of osteolysis nor needed revision. As such, the clinical relevance of the wear rate differences is potentially less significant.

Safety Evaluation of the Wear Life of High-Speed Railway Bridge Bearings by Monitoring Train-Induced Dynamic Displacements

Bridge bearings experience numerous small-amplitude displacements under environmental loads. The continuous cyclic accumulations of these small-amplitude displacements will result in severe wear on the poly-tetra-fluoro-ethylene (PTFE) plates in the bridge bearings, which seriously endangers the service life of bearings. Traditional method directly uses the linear wear rate of cumulative displacements in a short period to evaluate the wearing life, but the linear wear rate only in a short period such as several days may not represent the characteristics in the whole bridge service life. Hence, this research takes the spherical steel bearings of the Nanjing Dashengguan Yangtze River Bridge as a study object. The cumulative dynamic displacement (CDD) under the action of a single train and the cumulative bearing travel (CBT) under the continual actions of many trains are studied using the monitored longitudinal displacement data from spherical steel bearings. Furthermore, the probability statistics and the Monte Carlo sampling simulation for CDD are studied, and the safety evaluation method for bearing wear life in the real environment is proposed using a reliability index regarding the failure probability of monitored CBT over the wear limit during service lifetime. In addition, safety evaluation on the bearing wear life was performed to assess the condition of spherical steel bearings in the real service environment. The results can provide an important reference for analysis on the bearing wear life of long-span railway bridge structures.

Estimating the osteolysis-free life of a total hip prosthesis depending on the linear wear rate and head size

We present a model to estimate the osteolysis-free life of total hip arthroplasty, depending on linear wear rate and femoral head size. An estimate of the radiologic osteolysis threshold was calculated, which was based on volumetric wear. The osteolysis-free life of the cup was estimated from the quotient of the osteolysis threshold and volumetric wear rate, which was calculated from the linear wear rate. The impact of the direction of linear wear was determined by sensitivity analysis. From our review, we calculated a weighted mean polyethylene volume of approximately 670 mm3 as osteolysis threshold. Osteolysis-free life of less than 20 years was estimated for linear wear rates of 50 µm/year for head sizes of 32 mm or more, or for linear wear rates of 100 µm/year for any head size. For head sizes of 36 and 40 mm with a linear wear rate of 50 µm/year, the osteolysis-free period is estimated to be only 14.10 and 11.42 years, respectively. Sensitivity analysis showed reasonably robust results. With the aim of osteolysis-free life of more than 20 years, our study presents a viable model to determine maximum possible head size for articulations. Osteolysis-free period for 36 and 40 mm head sizes are far too low for conventional polyethylenes. As the threshold wear volume for highly crosslinked polyethylene is, as of yet, unknown, more research is warranted before our model can be generalized to XLPE.