Fig 2 - uploaded by Ridha Mnif
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General picture of the developed tribometer with the following components: 1, support; 2, electric armoire; 3, column guide; 4, fixed plate; 5, support jack; 6, jack; 7, intermediate plate; 8, torque sensor; 9, rack and pinion; 10, clamping force sensor; 11, set screws; 12, ball valve (color figure available online).
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In this article, we studied and explored the impact of viscoelasticity on the friction and wear behavior of pure polytetrafluoroethylene (PTFE), carbon–graphite PTFE composite, and glass fiber–MoS2 PTFE composite. Tests were carried out using a specific reciprocating tribometer for valve seal application. The worn surfaces of the PTFE composites an...
Citations
... Even if EP develops relatively higher friction coefficient than that of PTFE, it offers higher durability and allowable bearing resistance. Notably, a long-term friction test showed that the sliding distance of EP is 2 to 5 times longer than that of PTFE [15] with a 3 times higher friction coefficient [16][17][18][19][20]. Such types of friction materials are lubricated to make smoother behavior between upper and lower bearing plates. ...
... Even if EP develops relatively higher friction coefficient than that of PTFE, it offers higher durability and allowable bearing resistance. Notably, a longterm friction test showed that the sliding distance of EP is 2 to 5 times longer than that of PTFE [15] with a 3 times higher friction coefficient [16][17][18][19][20]. Such types of friction materials are lubricated to make smoother behavior between upper and lower bearing plates. ...
Friction material, as the main component in a bearing support, allows frictionless behavior between the two connected structures. Previous studies on friction material considered polytetrafluoroethylene (PTFE) and attempted to analyze the resulting friction behavior balance. However, aging PTFE loses its frictionless performances, because PTFE is crushed, causing it to tear, or the lubricant is removed. The performances of the friction material should thus be maintained to preserve the performance of structures. To overcome these issues, this study applies a ceramic friction material owing to its advantages of high strength, low friction, and low deformation. The frictional behavior is investigated on a full-scale model using Finite Element Analysis (FEA) according to the edge type of the ceramic friction material. The main design variables include four edge types, namely, general, camber, round and taper types. The results confirm that the modified edge types (camber, round and taper type) reduced the stress and deformation which, in turn, improved the friction behavior.
... As previously mentioned, pipeline gasket applications made of PTFE require the operating point to be less than the yield stress [8] for proper sealing ability and lifetime and to maintain operation below the plastic region. Mnif et al. [9] details the small strain viscoelastic response and tribological behavior of pure PTFE (and PTFE composites) in 1/4 turn ball valve seals. Jemaa et al. [10] also presents the development of a tribometer for viscoelasticity studies of the PTFE ball valve seals with operating strains of about 0.5%, well below the yield strain of 2.9% as measured in the work. ...
PTFE and filled PTFE are used in sealing applications such as rotary valves, quarter-turn ball valves and pipeline gaskets, among others. Many times, these seals are designed to operate below their yield point such that plastic effects are negligible and viscoelastic effects dominate. This may lead to leakage since these devices are placed in service environments that are subjected to vibration. In seals made of viscoelastic materials, this vibration can lead to separation of the seal faces due to the delayed recovery of the material. In this paper, the isothermal viscoelastic dynamic response of a PTFE seal subjected to a harmonic input and static preload from an ideally rigid opposing face is examined. The model is a hybrid that combines the Golla–Hughes–McTavish finite element approach, a delayed recovery creep model and a penalty method contact model. Parameters for the models are taken from experimental data using a Dynamic Mechanical Analyzer test for pure PTFE material. Results for a simple application show face separation magnitude as a function of frequency and harmonic displacement amplitude. Results show that face separation occurs in PTFE seals even for small amplitude harmonic vibrations and that this is due to delayed recovery at low frequencies and to the viscoelastic damping at higher frequencies. A threshold of static preload is also found above which there is no separation and a leakage estimation is presented.
... The properties of PTFE and materials derived from them are being investigated quite extensively [63][64][65][66]. The insufficient properties of PTFE and materials based on it for the creation of viscoelastic behavior models were noted in [67]. ...
... The deformation qualitative patterns and the value ranges of the mechanical characteristics obtained by us are similar to the results of Tan et al. The dependences of the deformation and mechanical characteristics obtained in the framework of the work visually correlate with the results of other authors [64][65][66]. Now, our group is engaged in the description of the materials viscoelastic behavior using the Prony rows. ...
The novel results reported here present qualitative and quantitative regularities of the deformation behavior of a spherical bearing with a different location and inclination angle of the antifriction layer. A number of topical problems encountered during the assessment of the performance bearings are considered in the work. The spherical bearings of the bridge span are investigated. Structures are load-bearing elements of transport systems. They perceive thermal power loads from the bridge span. The temperature problem is not considered in this study. In this paper, a comparative analysis of the bridge spherical bearing operation at different antifriction layer locations was performed. Two bearing geometries are considered: the interlayer is pressed in a spherical segment (classical geometry); the interlayer is pressed into a recess located in the lower steel plate. The six modern antifriction materials considered proved suitable to some extent as contact unit sliding layers for various purposes. Additionally, the influence of the inclination angle of the antifriction layer end face on the structure operation for all sliding layer material variants was analyzed. It has been established that the bearing design with an interlayer in the lower steel plate has a more favorable deformation behavior. Changing of the inclination angle of the antifriction layer end face leads to a decrease in the maximum level of contact parameters and deformation characteristics for all the considered structures.
... The studies showed a decreased tendency in friction and/or wear behaviors of the composites which depended on the type and the amount of the additives. In this field, several industrial applications can be improved by the incorporation of such fillers (Deng et al. 2011;Mnif et al. 2013). The self-lubrication capacity of graphene nanoplatelets (GNPs) incorporated to a Poly(etheretherketone) matrix was studied by Puértolas et al. (2019). ...
Two disjoint filler materials in a powder form are added to a polycarbonate (PC) matrix. The micro sized additives are Graphite (Gr) and molybdenum disulfide (MoS2) introduced as layered solid lubricants. Two distinct development methodologies are employed in order to prepare the composites; the first process is industrial by using directly an injection molding machine, while the second process is composite preparation in a laboratory scale. The experimental results of the two process are compared. From friction and wear tests, it is established that MoS2 particles improved the wear resistance and reduced the coefficient of friction of steel/PC contact with both development methodologies. On the contrary, Gr decreases the tribological properties of PC. Fracture morphologies and x-ray micro-tomography are performed to characterize the microstructural aspects of PC/solid lubricant composites. Micrographs show microcracking, filler agglomeration and the presence of voids with direct injection molding. Besides, the composites present poor scratch resistance properties. The different results are improved with the second development methodology including the powders surface treatment by an amino-silane and mechanical mixing with the PC matrix.
... The studies showed a decreased tendency in friction and/or wear behaviors of the composites which depended on the type and the amount of the additives. In this field, several industrial applications can be improved by the incorporation of such fillers (Deng et al. 2011;Mnif et al. 2013). The self-lubrication capacity of graphene nanoplatelets (GNPs) incorporated to a Poly(etheretherketone) matrix was studied by Puértolas et al. (2019). ...
ISF process is a promising flexible process that attracts several researches during the last decade. Applied on a CNC machine thin sheet are shaped through incremental plastic deformation trigged by a tool path programmed with a G-Code. This paper presents an experimental investigation on Single Point Incremental Forming applied on NC turning machine to manufacture revolved parts made of AA1050-H14 material. The idea is to use a 2-axis tool path strategy through the program of a paraxial roughing cycle used in machining to bore cylindrical parts. In fact, using this program, sheet metal can be shaped by incremental plastic deformation to the desired part. The effect of penetration increment, the shape of the final part on formability, appearance of cracks and the part finishing quality is analyzed. Results carried out show the efficiency of this tool strategy to manufacture parts usually manufactured through a 3-axis milling strategy in SPIF process. Certainly, SPIF applied in NC lathe gain the advantage of a rapid procedure and a low cost.
... This leads to the consequence that in tribological investigations of plastics, the resulting tribological properties (static and sliding COF, wear rate) cannot be considered, excluding the thermomechanical and viscoelastic properties of the material. For example, this fact is discussed in [25] with regard to the temperature influence and in [26] with regard to the long-term behaviour (creep, relaxation). With reference to the results of Figure 8 and the fact that in most engineering applications the aim is to minimise the tribological parameters, the variation of the infill density is limited to the range of 70% to 90% for the following test series based on a definitive screening design. ...
In recent years, additive manufacturing methods such as Fused Layer Modeling have been continuously improved by industry and research institutions. In many cases, the influence of process control on the mechanical component properties is being investigated. Influencing parameters include the infill and its orientation as well as patterns. Extrusion parameters such as the volume flow, which can be influenced by the speed, the line width, and the layer thickness, and the temperatures, which determine the interlaminar bonding between the lines and layers, are relevant as well. In this contribution, the influence of process control on the tribological properties of cylindrical tribo-test specimens made of polybutylene terephthalate is investigated. Using a reciprocating pin-on-plate tribo-tester, the static and dynamic friction forces as well as the linear wear is determined. The results show a significant influence of the orientation and density of the infill on the tribological properties. Due to the process-specific large degrees of freedom, the advantage of a load-compatible individualisation and consequently the optimisation of tribologically exposed components is given compared to conventional manufacturing processes.
... Because of the high conductivity of the metal dust, a polytetrafluoroethylene (PTFE) casing was specially customized. PTFE is a polymer obtained by polymerizing tetrafluoroethylene, and has excellent chemical stability, corrosion resistance, sealing properties, high lubricating non-stickiness and electrical insulation [29]. It was placed on the ignition electrode rod to prevent the electrode rod from breaking the uniformity of dust distribution when the electrode was energized. ...
... The output of this torque cell was stored during each experiment via data acquisition. The variation of the friction coefficient with the number cycles was calculated following equation (1) (Mnif et al., 2013). ...
... Compression tests were carried out using the tribometer equipped with a comparator fixed on the two surrounded plates of the valve. The cross-sectional area (S), between the ball and seal, was a truncated cone and was calculated following equation (2) (Mnif et al., 2013). ...
The ball valve seals are exposed during their use to thermal gradients (alternating the flow of cold and hot water), static loading (clamping force) and cyclic loading (alternating opening and closing) which can be sources of valve failures. The ball valves usually fail as a result of different failure modes such as wear, plastic deformation and corrosion. In order to describe these modes a failed ball valve which was belonged to a sanitary installation is investigated. The investigation of the failure was carried out by using several experimental tests including optical microscopy and Scanning Electron Microscopy (SEM). Tests were performed on a specific reciprocating tribometer for ball valve seals application. Experimental results revealed that the friction behaviour of polymeric seal depends strongly on the clamping load of seal and the manipulation frequency of counterface ball. Optical microscope observation of the worn surface showed that strong adhesion of the polymeric transfer layer to the counterface ball.
... The output of this torque cell was stored during each experiment via data acquisition. The variation of the friction coefficient with the number cycles was calculated following equation (1) (Mnif et al., 2013). ...
... Compression tests were carried out using the tribometer equipped with a comparator fixed on the two surrounded plates of the valve. The cross-sectional area (S), between the ball and seal, was a truncated cone and was calculated following equation (2) (Mnif et al., 2013). ...
The ball valve seals are exposed during their use to thermal gradients (alternating the flow of cold and hot water), static loading (clamping force) and cyclic loading (alternating opening and closing) which can be sources of valve failures. The ball valves usually fail as a result of different failure modes such as wear, plastic deformation and corrosion. In order to describe these modes a failed ball valve which was belonged to a sanitary installation is investigated. The investigation of the failure was carried out by using several experimental tests including optical microscopy and Scanning Electron Microscopy (SEM). Tests were performed on a specific reciprocating tribometer for ball valve seals application. Experimental results revealed that the friction behaviour of polymeric seal depends strongly on the clamping load of seal and the manipulation frequency of counterface ball. Optical microscope observation of the worn surface showed that strong adhesion of the polymeric transfer layer to the counterface ball.
To explore the potential wear performance of commonly utilized hydraulic system polymer components, we investigated the effects of different working conditions on the frictional and wear behaviors of three polymer sealing materials in this study. Polytetrafluoroethylene (PTFE), nylon (PA), and polypropylene (PP) composites were prepared using copper (Cu) and glass fiber (GF) as fillers. The tribological and wear properties (wear rate, surface appearance, wear patterns) of the sealing composites were evaluated. The results showed consistent trends toward increasing average coefficient of friction as load and speed increased for PTFE. The incorporation of filler improved the wear resistance of the composites. The addition of Cu particles showed lower coefficient under higher load and sliding speed. PA with continuous glass fiber (CGF) sealing composites showed lower coefficient, less wear volume, and relatively smoother wear zone surfaces than PTFE-based composites or PP with short glass fiber (SGF). We propose that PA-CGF outperforms other materials in regards to fatigue and friction and wear even under extremely high silding speed,as well as sealing properties.
