Investigation of friction and wear behavior of hydroxyl-functionalized graphene nanoplatelets filled elastomer nanocomposites

The use of unfilled pure elastomer parts is limited in friction wheels, roller tires, sealing elements, and dynamic friction air suspension applications requiring high wear resistance. This study investigates the mechanical and tribological properties of new nanocomposites obtained by adding hydroxyl-functionalized graphene nanoplatelets at 1, 4, and 8 phr (parts per hundred rubber) ratios to the carbon black filled main rubber compound of sealing elements designed for axle hubs. The synergistic effect of nanofiller materials on the wear behavior of nanocomposites was tested with a block-on-ring wear tester under dry sliding conditions at 1000 rpm and 15 N normal load conditions. The worn surfaces were examined with scanning electron microscopy and circularly polarized light–differential interference contrast topology microscopy to reveal the wear mechanism. The addition of functionalized graphene nanoplatelets to the nanocomposite compound caused significant changes in tensile strength and elongation values by changing the cross-link density. The wear rate of nanocomposites prepared with graphene nanoplatelets at 1, 4, and 8 phr ratios was 11.15%, 25.24%, and 36.54% lower than the main rubber mixture used, respectively. While the hysteresis loss decreased by 14.83% at 1 phr, this value increased in other filler ratios. Significant differences in temperature change occurred as the amount of filler increased. After the test, the temperature values of nanocomposites with 1 and 4 phr filler ratios were between about 85–89°C, while it was measured as 99°C in nanocomposites with 8 phr filler ratios. It has been observed that the homogeneous distribution of two-dimensional carbon allotropes such as graphene nanoplatelet added to the rubber matrix at the optimum rate will improve tribological properties such as better surface lubrication, low wear rate, and low friction coefficient.

Pilot plant tests to demonstrate the functionality of sealing elements made of salt cut bricks

The long-term safe containment of high-level radioactive waste in a repository in rock salt is ensured if the geological barriers in conjunction with the geotechnical barriers are permanently impermeable to fluids. As such, an essential factor in underground disposal is to confirm that the interfaces between the biosphere and the lithosphere, i.e., shafts, boreholes, and galleries, created during the excavation of underground cavities can be sufficiently tightly sealed. An essential element of the sealing system required to this end is shaft closure. All shaft closure concepts developed thus far include sealing and supporting elements in repository shafts, but differ in the arrangement of these structural elements and the materials used. The materials currently proposed and planned for the construction of the sealing elements include: clay/bentonite, asphalt/bitumen, crushed salt, and salt/sorel cement. In addition to the materials mentioned above, a research project funded by the German Federal Ministry for Economic Affairs and Energy (Bundesministerium für Wirtschaft und Energie, BMWi) is investigating the possibility of integrating a layer of salt cut bricks several decameters to 100 m thick into the shaft closure system as a sealing element that provides the option of allowing the geological barrier to heal in the long term. Like the surrounding rock mass, the salt cut bricks are made of natural rock salt. According to this plan, the profile of the bricks is designed to minimize joint volume as far as possible by cutting them to match the geometry of the shaft. The joints between the salt cut bricks can either be filled with, for example, a supersaturated salt solution, Magnesium building materials, molten salt, crushed salt, etc., or directly brought into contact by wetting the surface of the salt cut bricks. Once the salt solution has hardened (cooling of the solution, evaporation of the mixing water), only the pore space in the crushed-salt joint sealant filled with salt solution or air, or the joint volume resulting from the mismatch between individual rock salt bricks are susceptible to a reaction. This means that the sealing element consisting of salt cut bricks develops early supporting pressure against the creeping rock salt of the rock mass compared to crushed salt, has a low initial porosity and already shows a strong sealing effect in the short term (regression of the loosened zone). One can also assume that cohesive bonding between the surrounding rock and the sealing element can already be achieved by introducing the joint filling or by wetting the contact surfaces of the salt cut bricks (no or reduced separation planes in the contact zone). Essential prerequisites for the investigation of the geomechanical-geohydraulic effectiveness of a sealing element made of salt cut bricks included the development and construction of a pilot plant to analyze the mechanical and hydraulic material properties of the bonding system comprising salt cut bricks and joint sealing (FKZ 02E11223, FKZ 02E11425), as well as preliminary investigations on the production of salt cut bricks and joint sealant (→ cutting technique/processing of salt cut bricks; maufacture/workability of jointing material) and on the spatial arrangement of the salt cut bricks (→ avoidance of continuous axial joints in the bonding system, Fig. 1). The presentation includes the results of the research work on the development, construction and commissioning of the pilot plant, as well as the first successful test results demonstrating the functionality of sealing elements made of salt cut bricks.

Swelling Elastomers and Tubular Expansion—Numerical Investigation

Swell packers were initially used for repair of old and damaged wells, but they are now increasingly used for higher productivity and profitability through developments like slim well design and reduced-cement or cementless completions. Solid expandable tubular (SET) technology has gained popularity in the petroleum development industry as it can reduce well costs and improve well performance. A conical mandrel is pushed or pulled through a petroleum tubular, either hydraulically or mechanically, to expand it (in-situ) to the desired diameter. In SET applications such as water shutoff and zonal isolation, swelling elastomers are an obvious choice as a sealing material. For proper downhole deployment of swell packers in SET applications, it is important to have a good idea about their behavior under a given set of field conditions. Design and manufacturing of SET applications using swelling elastomers as sealing elements also needs some sort of seal performance analysis.

Analysis of the influence of cutting conditions on the roughness of the surface layer when machining a composite material based on thermally еxpanded graphite

The current trend of replacing metal alloys with composite materials in the manufacture of various types of plain bearings, sealing elements of Assembly units, anti-friction bushings, and other machine parts is very promising for the development of many industries. However, in the manufacture of composite material products by modern methods, such as extrusion, pressing, and injection molding, various types of defects characteristic of these types of processing occur, resulting in the required parameters of the quality of the working surfaces of parts are not provided. This leads to the need for additional mechanical processing the quality of which largely depends on the reliability and durability of the functioning of parts and mechanisms. The article analyzes the main parameters that affect the quality of the surface obtained during turning for metal alloys, as well as for composite materials. The method of obtaining blanks by pressing from the material under consideration was developed, the technological equipment necessary for the research was designed and manufactured, a plan was developed for conducting a full-factor experiment with the creation of a model in the Mathcad program, and an active experiment was carried out to determine the influence of cutting mode parameters on surface roughness. Given the results of the study on the basis of which conclusions about the dependence of various cutting parameters on the quality of the surface layer, defined by the nuances of turning the considered composite material, practical recommendations that will positively affect the timing and success of implementation of fabrication of parts from this material.

Closing Force Evaluation of a Sample Return Capsule for a Phobos Sample Return Mission

The mission objective of the Phobos Sample Return is to collect and return 100 g of Phobos’ surface material to Earth inside a tight enclosure composed of a Vault, a Sample Container and sealing elements. One important aspect of the project was the development of a closing mechanism capable of ensuring a pushing force high enough compared to the available force of the robotic arm (40 N). The need for a higher pushing force derived from the design tests which were carried out to experimentally determine the necessary force to overcome the resistance of the sealing element when the vault is closed. Two types of sealing elements, custom made for this project, along with two SC with different geometrical shapes in the sealing area were tested. For better accuracy, the tests considered the imposed operational temperature domain for the vault, ECSS standards and the test rig set-up being performed at environmental temperature (+20 °C), −20 °C, −60 °C and +70 °C. The results of the tests highlighted that the negative temperature has a significant influence over the closing force, as this force is increasing once the operational temperature is decreasing. Based on the work performed, the most suitable type of sealing element was identified, in particular the piston geometry which allows a smaller force to close the vault.

Metallurgical Failure Investigation of Fractured Spring Seals

Elastic sealing elements used in combustion chamber assemblies of heavy-duty gas turbine engines used for power generation fractured from high cycle fatigue failure. The subject assembly was burner rig tested in a special testing facility. It was speculated that the affected spring seals likely failed due to forced excitation during burner rig testing, since no material imperfections or fabrication flaws, such as spot weld imperfections, were detected that could have contributed to the failure.

IMPROVING THE STRENGTH CHARACTERISTICS OF PACKERS' SEALING ELEMENTS MADE OF POLYMER NANOCOMPOSITES.

On the basis of a micromechanical model of the tensile strength of a polymer composite, it is shown that, in contrast to the case of adhesion between two polymers, when there is a linear correlation between the thickness of the interfacial region and the level of interfacial adhesion, the strength of the interface in nanocomposites of the "polymer-high modulus filler" type decreases with growth. its thickness. The dependence of the tensile strength of polymer nano-composites on the properties of the material and the level of interfacial interaction has been established. Keywords: strength model, interfacial adhesion, nanocomposite, seal material, packer.

Bottom Sediments from a Dam Reservoir as a Core in Embankments—Filtration and Stability: A Case Study

A possibility of using bottom sediments from dam reservoirs in earth structures was considered. Sediments from the Rzeszow reservoir (Poland) were used as research material, which, according to geotechnical standards, were classified as low permeable silt with high organic content. As fine, cohesive soil with a low coefficient of permeability, the sediments can be used in sealing elements of hydraulic engineering embankments. In order to verify the suitability of the sediments, stability and filtration calculations were carried out for embankments with a sealing in the form of a core made of the sediments. It was stated that by using a core made of sediments, the volume of seepage on the downstream side during continuous or variable backwater was significantly lower in relation to an embankment without a core, and the phreatic line did not extend to the downstream slope. It is estimated that, in the case of a planned dredging in Rzeszow Reservoir, the amount of dredged sediment would exceed 1.5 million m3, and therefore, the possibility of their economic use is essential. The search for materials that could replace natural soil in earthen structures is an important issue from both the ecological and economic points of view.