Papers by Wojciech Wieleba
Tribologia
The paper describes the effects of gamma radiation doses on the tribological and mechanical prope... more The paper describes the effects of gamma radiation doses on the tribological and mechanical properties of selected thermoplastic polymers: PEEK, PEI, PET, and PA6. Samples of those polymers were irradiated with gamma rays of energy 1, 1.2, 3, 4, 5 MeV and with the intensity of the radiation beam 4, 7, 10, 30, 40 μA. With an increasing dose of radiation, properties such as microhardness, the friction coefficient of polymers, and the wear rate are changed. The chemical structure of the irradiated polymer may be changed by crosslinking but also by chain scission. The modified polymers may be used in medical science, electronics, and space technology. In this article, we report the results of steel C45 – thermoplastics (PEEK, PEI, PET, and PA6) friction couple during the slip motion. The analysis is focused on the friction coefficient, wear rate, and microhardness. Kinematic parameters of the experiment in slide movement were constant and defined by the following values: contact pressur...
Tribologia
The paper presents a description of the mechanical construction, measuring and control systems an... more The paper presents a description of the mechanical construction, measuring and control systems and the possibilities of a new type tribological testing device. The design was developed and built at the Department of Fundamentals of Machine Design and Tribology of Wroclaw University of Science and Technology. Described tester allows the investigate a friction and wear of components such as fibrous tapes, ropes, plaitings or fibers themselves in contact with solid materials. The paper describes in detail the construction of drive and the load pneumatic system. The innovative system of the device such measurement equipped with piezoelectric sensors and an experimental fixing unit of tested components also have been described. Work includes diagrams of used control and measurement systems and the central lubrication system. As a test the polyethylene cable in contact with brass rods has been examined. The results of this studies were been also presented in the paper.
Tribologia
The effect of tensile deformation on polymer structures and their mechanical properties is descri... more The effect of tensile deformation on polymer structures and their mechanical properties is described in various papers. However, the majority of articles are focused on high deformation (a few hundred percentiles) at increased temperature. It causes changes in orientation and the crystallinity ratio. The authors of this paper asses the influence of strain (max. 50%) on hardness and the coefficient of friction (polymer–steel A1 couple) for selected polymers. The deformation was conducted at room temperature and maintained during tests. There was a significant reduction (up to 50%) of hardness after deformation, in the case of all examined polymers. In the case of PE-HD, the coefficient of kinetic friction almost doubled its value (89% increase). The reduction of the coefficient of static friction for sliding pairs that include PTFE and PA6 was about 26% (in comparison with non-deformed polymer). For all investigated polymers, hardness increased over time (up to 40% after 24 hours). C...
Polymer materials are increasingly being used for sliding machine elements due to their numerous ... more Polymer materials are increasingly being used for sliding machine elements due to their numerous advantages. They are used even where they are deformed and in such a state they interact frictionally e.g. in machine hydraulics or lip seals. Few publications deal with the influence of deformation, which is the effect of e.g. assembly on tribological properties of polymeric material. This deformation can reach up to ε ≈ 20% and is achieved without increasing the temperature of the polymer material. The paper presents the results of investigations in which high-density polyethylene (PE-HD) was maintained in deformation by means of a special grip (holder). The wear of the sample was significantly higher than that of the undeformed sample. This effect persisted even after partial relaxation of the stress in the sample after 24 hours. Additional investigations were carried out to explain the obtained results. There were the microscopic observations of the surface after friction, measuremen...
Tribologia
This article presents the results of studies on the tribological properties of linear wear and ki... more This article presents the results of studies on the tribological properties of linear wear and kinetic friction of polylactide processed by 3D printing (FFF) and injection moulding. Research was conducted on a pin on disc apparatus, and the test specimens used were polylactide cylinders with the counter specimen of C45 steel disc. Research was planned and executed with the planned experiment method for two variables: velocity of the counter specimen and pressure. The range of specified values was in the following sections: p = 0.2;0.6 MPa and v m s = 0.2;1.0 . The conducted experiment had a target of defining the influence of a somewhat new method of 3D printing on the tribological properties of materials that might find application in prototyping plain bearings.
Tribologia
Sliding cooperation of materials with different hardness (deformability), e.g., a polymeric mater... more Sliding cooperation of materials with different hardness (deformability), e.g., a polymeric material cooperating with metallic materials, occurs in machine elements in one of the following two variants: a conventional pair or a reverse pair. In the case of the conventional sliding pair, the deformation area (contact area) of the sliding materials does not move on the surface of the polymer element during their cooperation. In the case of reverse pairs, the contact surface changes its position when moving on the surface of the polymer element. Depending on the variant of the sliding pair, the differences in the friction and wear process of polymer material can be observed. Tribological investigations of chosen sliding pairs (elastomer on steel or steel on elastomer) in the static friction were carried out on the rig. The polymeric materials selected for the tests were thermoplastic elastomers TPU, PUR, and silicone rubber SI. These materials co-operated with C45 steel in the differen...
Tribologia
The article presents the results of studies on the influence of the addition of graphite to a PLA... more The article presents the results of studies on the influence of the addition of graphite to a PLA filament on linear wear and the coefficient of friction. A cylinder of 8 millimetre diameter manufactured in Fused Filament Fabrication process, popularly called 3D printing was used as a specimen. Studies were conducted on pin-on-disc testing machine, in which the cylinders mentioned above were paired with a steel disc – the counter-specimen. Specimens used in research were enriched by 5%, 10%, 20%, and 30% of graphite in comparison to the base filament – Natural PLA, which were not enriched with any additions that could improve its tribological properties. The experiment was conducted as a preliminary research. The gained results create a basis to select the optimal composition of additions to the PLA to create a filament with better tribological properties.
Tribologia
Friction and wear of materials with additional deformation or stress is not a broadly described c... more Friction and wear of materials with additional deformation or stress is not a broadly described case. However, scientific publications considering this issue point out that additional deformation and stress ought to be taken into account during wear and friction analysis. In this article, the influence of strain in thermoplastics (POM, PTFE, PE-HD, PMMA) over the friction coefficient is described. Materials were deformed under tensile stress and examined after 24 hours. For specimens in which plastic strain was maintained, the decline of hardness (PE-HD: approximately 70% decrease, PTFE: approximately 40% decrease) and the reduction of the coefficient of kinetic friction (both PTFE and PE-HD: about 20% decrease) were observed. POM returned to its pre-deformed shape and PMMA was deformed without reaching its elastic limit. In these cases, only small changes in hardness (POM: approximately 10% decrease, PMMA: approximately 6% increase) and friction coefficients (maximum 4% change) occ...
Tribologia
Experience gained from the use of buses in urban conditions showed that the working conditions of... more Experience gained from the use of buses in urban conditions showed that the working conditions of friction elements of the braking system, ensuring traffic safety, are associated with high loads. This leads to the intensive wear and premature replacement of the worn friction components, which reduces the overall reliability of the brake system and road safety. On the other hand, the friction linings of brake mechanisms may act as abrasives that cause the wear of brake discs or drums. Their replacement during operation is associated with a significant increase in the cost of spare parts. Therefore, it is assumed that the determination of the tribological properties of the brake linings in the brake mechanisms, before their exploitation, will increase the efficiency and safety of the vehicles’ operation, which justifies the choice of the research subject matter for its real and practical significance. The paper presents the preliminary results of the research into the main elements of...
Tribologia
The article presents the results of tribological research into engineering polymers (POM, PEEK, P... more The article presents the results of tribological research into engineering polymers (POM, PEEK, PPS) cooperating in sliding motion with 316L steel and EN AW-2017A aluminium alloy in the presence of a liquid (water, hydraulic oil HLP68). This type of friction pair may occur in hydraulic systems (gear pumps, valves, etc.). For comparison, additionally, the results of tribological research carried out in dry friction conditions have been shown. In addition, the results of microscopic study of the sliding surfaces of polymeric materials have been presented. Analysis of the test results allows one to describe the processes of friction and wear of the studied sliding pairs.
Proceedings of the 5th International Conference on Mechanical Engineering, Materials and Energy (5th ICMEME2016), 2016
А research of microstructure of Ti-Al coatings received by method of the mechanical alloying on t... more А research of microstructure of Ti-Al coatings received by method of the mechanical alloying on the surface of titanium was conducted by the scanning electron microscopy method and X-ray structure analysis. The morphology of coatings is formed depending on the efficiency of powder components staying in the zone of dynamic impact of spheres blow. The shift of the Ti diffraction line was found which is explained by internal stress of first order, induced as a result of spheres blows. It is supposed that the defect structural state promotes the increase in reactivity of components of processed materials, anomalously high mass transfer and a solid-phase mechanical alloying.
Nr kompozyty PTFE, procesy tribologiczne, ciep³o tarcia, temperatura tarcia Wojciech WIELEBA *
Tribologia
W pracy przedstawiono badania właściwości adhezyjnych stali i polimerów w kontekście zastosowania... more W pracy przedstawiono badania właściwości adhezyjnych stali i polimerów w kontekście zastosowania ich na węzły tarcia. Najpowszechniejszą metodą oceny właściwości adhezyjnych ciał stałych jest pomiar kąta zwilżania. Pomiar kąta zwilżania został użyty do wyznaczenia swobodnej energii powierzchniowej stali i polimerów oraz pracy adhezji dla skojarzeń stal–polimer. Badaniom poddano polietylen o ultrawysokim ciężarze cząsteczkowym, polieteroeteroketon, polioksymetylen, politetrafluoroetylen oraz stal austenityczną 316L i stal C45 o różnej twardości. Analiza wyników badań ukazała silną zależność między pracą adhezji a współczynnikiem tarcia statycznego oraz brak wpływu twardości stali na jej swobodną energię powierzchniową.
For carrying out the tribological tests four materials that are commonly applied for dental impla... more For carrying out the tribological tests four materials that are commonly applied for dental implants were used. They were two alloys with precious metals matrix – Degudent Kiss and Degulor M, one alloy with cobalt matrix – Brealloy 270 and one ceramic material –zirconium oxide. Samples that were used for investigations have planar cuboid shape. Contact area during testing was 13.85 mm2 for Degudent Kiss, 6.97 mm2 for Degulor M, 56.70 mm2 for zirconium oxide and 13.01 mm2 for Brealloy 270. The countersample was a thin layer of polymeric composite (applied in prosthodontics) distributed on a flat bar. Kinetic friction tests (Fig.1.) were run with the aid of a special testing stand which was designed especially for friction coefficient investigations in case of reciprocating movement. The tester was additionally equipped with micrometer screw in order to enable also static friction measurements. The investigations consist in the observation of friction force change during rectilinear r...
Tribologia
Progress of engineering science and technology has an essential influence on the medicine develop... more Progress of engineering science and technology has an essential influence on the medicine development during last 40 years. Combination of these two fields of knowledge bears fruit with production of different kinds of implants. Their usage significantly improves life convenience of many people. Spine stabilizers are the most frequently deployed ones. Unfortunately application of them is connected with numerous problems. Among other things we can distinguish also these that have biotribological background. Usually they are revealed during exploitation. It is because human-made construction and materials are only an attempt of mapping highly advanced nature-made structures and solutions. The author of this article presents results of the static friction coefficient tests as a unit pressure function. Three groups of materials have been examined – austenitic steels (steel 316L), cobalt-base alloys (vitalium) and titanium alloys (Ti6Al14V). Obtained results shows a rapid increase of the...
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Papers by Wojciech Wieleba