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For a number of polymers with a variety of chemical structures and different properties, we have performed scratch-resistance tests and investigated the profiles of the grooves formed using a profilometer. Three main kinds of material response are seen: plowing; cutting; and densification. The cross-sectional areas of the grooves include the groove...
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... From the figure, we can observe a minimum value of micro-hardness with the substrate from pure LLDPE followed by a continuous increase. It is worth remembering that there is an exponential relationship between the material moved during micro-scratch testing and its Vickers micro-hardness: the area of the displaced material (groove and two top ridges) is lower when the hardness is higher [36]. This last result will be further discussed in the subsequent section. ...
... This last result will be further discussed in the subsequent section. when the hardness is higher [36]. This last result will be further discussed in the subsequent section. ...
... The transfer film contributed to the wear process in place of hard steel asperities. It was experimentally established in [36] that ultra-wear-resistant polymer/metal composites were formed due to the hardening of their surface layers upon friction. Tribosynthesis and tribodestruction are the two transformations involved in the tribochemical processes, leading to an increase in adhesion between the filler and the polymer, especially with the production of local temperature flares upon protrusions of the counterbody with the collisions of the solid filler particles. ...
This research work focuses on the development and analysis of copper-filled linear low-density polyethylene (LLDPE) coatings deposited on LLDPE substrate via a thermocompression process. A dry mechanical mixing technique is employed to mix the copper–LLDPE powders. This relevant technology aims to develop new solid lubricating layered composite coatings without a negative environmental impact. Four different materials of the coatings are considered, i.e., LLDPE + 2 wt.% Cu, LLDPE + 6 wt.% Cu, LLDPE + 10 wt.% Cu and LLDPE + 20 wt.% Cu. The microstructural characterizations indicate a good degree of dispersion and adhesion between the continuous and dispersed phases at 20 wt.% Cu coatings. The mechanical properties of the pure polymer and the fully filled composite materials are investigated experimentally using tensile tests and Micro-Vickers hardness. The stiffness, hardness and mechanical strength of the composites are enhanced. Friction tests are also carried out via a linear reciprocating sliding tribometer. The incorporation of copper powder has a significant improvement on the friction and wear properties of the developed coatings. Higher copper powder loading provides a lower friction coefficient and wear volume loss. The best tribological performances are obtained with the LLDPE + 20 wt.% Cu coating. The wear mechanism of the LLDPE substrate is severe adhesive wear, and it becomes mild abrasive wear in case of the 20 wt.% Cu coating.
... In the deposition regions of both samples, the viscoelastic patterns were formed by three regions. The central groove [49,50] has a width of around 10 mm, presented along the Y-axis in Fig. 3A2. Two minor grooves contain side-wing ripples beside the central major groove located at X = −10 and 10 mm along the Y-axis. ...
In additive manufacturing, modification of the viscosity of softened or molten metal plays a significant role in the development of mechanical properties distribution. Similar to soft polymers, molten or softened metal usually exhibits vastly different viscoelastic properties. During scratching tests, viscoelastic polymers undergo spatiotemporal stress development and relaxation, causing stress ripples to form on their surfaces. It is observed that friction stir-based solid-state manufacturing can yield similar stress ripples on softened aluminum alloys due to the linear motion of the deposition tool. Softened aluminum alloys exhibit viscoelastic and viscoplastic responses similar to polymeric material during the solid-state deposition process. In the final product, residual stress ripples appear on the surface of the metal alloy due to periodic residual stress relaxation, leading to oscillatory behavior from the bulk mechanical properties of the material. The orientation of the in-built stress pattern formed in the bulk of the additively manufactured metal alloy underneath the visually evident onion ring-like surface pattern formation is diametrically in the opposite direction. The experimentally observed results are consistent with analytical calculation and numerical simulations in terms of behaviors.
... Interface heating, which is mainly limited H r and H c both decrease with the increase in normal load, in agreement with the experimental results obtained by Sinha et al. [58]. As v increases, both d p and w s become smaller, resulting in larger H r and H c , consisting with previous results [80,108,109]. H r and H c can be used to characterize scratch resistance of material, and a larger H r or H c indicates a better scratch resistance [110]. Nevertheless, PPS has the highest hardness, but does not show good scratch resistance, since its optical morphology exhibits the roughest surface with severe damage, which is caused by its large elastic modulus [57,99]. ...
Microscratch test was carried out by Berkovich indenter on four thermoplastics of distinct characteristics: polytetrafluoroethylene (PTFE) is soft and self-lubricating; polycarbonate (PC) is an engineering plastic of good toughness; polyphenylene sulfide (PPS) is a hard and brittle material; and polyamide 6 (PA6) has good elastic recovery rate. Effects of sliding velocity on scratch responses of the four thermoplastics under different constant normal loads were compared and quantified. With the increase in sliding velocity, penetration depth, residual depth, residual scratch width, and contact scratch width decrease nonlinearly; scratch hardness and elastic recovery rate increase nonlinearly. PTFE, which has the smallest hardness, exhibits the largest penetration depth and scratch width, and the smallest scratch friction coefficient, implying its weakest scratch resistance. PA6 has the largest elastic recovery rate (greater than 80%), indicating its good scratch resistance. The surface morphologies of PPS and PC are sensitive to sliding velocity. The scratch friction coefficient of PPS is most sensitive to sliding velocity and increases significantly with the increase in sliding velocity, while scratch friction coefficients of PTFE and PA6 are insensitive to sliding velocity, and the scratch friction coefficient of PC is only sensitive to sliding velocity under small sliding velocities.
... UCS, K IC , and other rock mechanical parameters influencing how the fracture nucleates [7], fracture size and geometry, but fracture sizes and geometry adopted in hydraulic fracture design and modelling, Discrete Fracture Network (DFN) modeling, and Finite Element Modeling (FEM); are most often overestimated. Although scratch tests are applicable nowadays to several fields of science and engineering, ranging from strength characterization of rocks and cements/ceramics [8,9], to damage of polymers [10][11][12] and metals [13,14], and quality control of thin films and coatings [15,16]; the underlying rock failure mechanisms, characterization, and applications has not been fully explored. Although several researchers have attempted to evaluate and quantify UCS, fracture toughness, and other rock mechanical properties in conventional and unconventional reservoir rocks using indentation and scratch testing methods, but there remain differing opinions on the fundamental approach and principles to be adopted in estimating those parameters. ...
The scratch test is a quasi-non-destructive method made up of pushing a tool across the surface of a weaker rock at a given penetration depth. The unconfined compressive strength (UCS), fracture toughness (KIC), and other geomechanical parameters influence how geological materials fail, and how the succeeding fractures nucleate. Researchers have attempted to evaluate UCS, KIC, and other geomechanical properties in diverse rock formations through the scratch test method, but there remain differing opinions on the fundamental approach and principles to be adopted in estimating these properties. Therefore, the evaluation of geomechanical parameters and their impact on hydrocarbon exploration and exploitation, and underground storage remain an important issue for the energy industry. In this paper, we present a comprehensive review of the methods of approach, applications, and the mechanics of rock scratching. We showed the merits of utilizing scratch tests over other conventional methods of measuring and estimating geomechanical properties. Our review focuses on previous studies in the past few decades that utilized the scratch test method to investigate geomechanical properties and their impact on fractomechanical behavior. Finally, we highlight promising research areas of investigation to improve the application of the scratch test method. We envisage this advancement in our knowledge will improve the optimization of hydrocarbon exploitation, underground storage, and field-scale modeling for energy production operations.
... UCS, , and other rock mechanical parameters influencing how the fracture nucleates [5], fracture size and geometry, but fracture sizes and geometry adopted in hydraulic fracture design and modelling, Discrete Fracture Network (DFN) modeling, and Finite Element Modeling (FEM); are most often overestimated. Although scratch tests are applicable nowadays to several fields of science and engineering, ranging from strength characterization of rocks and cements/ceramics [6,7,8,9,10,11,12], to damage of polymers [13,14,15,16,17,18,19,20,21] and metals [22,23,24,25], and quality control of thin films and coatings [16,19]; the underlying rock failure mechanisms, characterization, and applications has not been fully explored. Although several researchers have attempted to evaluate and quantify UCS, fracture toughness, and other rock mechanical properties in conventional and unconventional reservoir rocks using indentation and scratch testing methods, but there remain differing opinions on the fundamental approach and principles to be adopted in estimating those parameters. ...
The scratch test is a non-destructive method made up of pushing a tool across the surface of a weaker rock at a given penetration depth. The uniaxial rock strength (UCS), fracture toughness (K IC ), and other geomechanical parameters influences how fracture nucleates, but fracture sizes and geometry adopted in hydraulic fracture design and modeling are most often overestimated. Although several researchers have attempted to evaluate UCS, K IC and other geomechanical properties in conventional and unconventional formations through scratch testing method, but there remain differing opinions on the fundamental approach and principles to be adopted in estimating those properties. Therefore, the evaluation of geomechanical parameters and their effect on hydrocarbon exploration, energy storage, and hydrocarbon exploitation remain an important issue for energy industry. In this paper, we present a comprehensive review of the methods of approach, applications, and the mechanics of rock scratching. We show the merits of scratch test over other methods of estimating rock mechanical properties. Our review focuses on over 50 previous experimental studies using scratch tests in the past few decades to investigate UCS, K IC and other geomechanical properties, including their impact on rock failure, fracture initiation and propagation. Finally, we highlight the fundamental research questions that are yet to be addressed. We envisage that advancement in our knowledge will improve optimization of hydrocarbon exploitation, energy storage, and field-scale modeling for energy production operations.
... Besides, PP and PTFE are long straight-chain polymers, which have only two types of chemical bonds (PP consists of C−H and C−C bonds, and PTFE consists of C−F and C−C bonds). 30,31 Their surface energies are low enough to form hydrophobic interfaces to yield effective lubrication. According to these friction results, the counterpart PTFE ball can improve the lubrication of the MXene coating obviously. ...
... It has already been reported that the hydrocarbon chains of PTFE tend to move during the transmission electron microscopy (TEM) observation. 31 In the Supporting Information (Movie S2), it is obvious to find the movement of this tribofilm along the interface, which identifies the composition of this sublayer as PTFE and confirms the movement of its skeleton under electron irradiation. This suggests that PTFE pushes away 2D Ti 3 C 2 nanoflakes and nanodiamond particles to occupy the bottom layer during sliding, which can protect these nanolubricants from rubbing- ...
The newly-emerging two-dimensional (2D) material of MXenes possesses lots of merits, which provide potential solutions for the lubrication issues in harsh conditions. Here, preliminary efforts were devoted to developing MXenes-based 2D composite coating and its anti-wear interfacial performance in ambient environments. Macro-scale and atomic-scale characterizations were utilized to explore the lubrication behaviors of the composite coating to clarify the influence of the coating composition and tribo-test parameters in the establishment of ultra-wear-resistant sliding interfaces. The results highlighted a unique lubrication mechanism for 2D MXenes composite coating. They suggested that the MXenes/nanodiamond coating exhibited almost no wear when rubbing against polytetrafluoroethylene (PTFE) ball. A nanostructured tribofilm with unprecedented bonding features was in-situ formed along the sliding interface. The ultra-wear-resistance highly depended on the combined effects of shielding and self-lubrication of PTFE, layer shearing of MXenes and self-rolling of nanodiamond. These discoveries clearly enrich the 2D material-based lubrication theories and offer technical guidance for designing and exploiting high-performance ultra-wear-resistant materials.
... As mentioned, work on lowering friction and mitigating tracks created by the moving intenter in polymers is pertinent. Such tracks have been studied in some detail (Brostow et al., 2007). Low friction-and low wear related to it-are important also in movable devices in aerospace systems investigated by Voevodin and his colleagues (1999). ...
We have quantitatively defined flexibility of polymers. Flexibility Y is not an inverse of the brittleness B, rather, the two equations are compared. The expression for flexibility includes the specific volume and the summation of the strengths of chemical bonds-a concept introduced by Linus Pauling. The flexibility is plotted as a function of dynamic friction, resulting in a representative single curve for polymers.
... As discussed earlier, the indenter leaves behind a groove and two top ridges along the groove. 48 We summarize the volumetric wear results for SWCNTs and MWCNTs in Tables V and VI respectively and in Fig. 8. ...
We have created hybrids of functionalized single wall carbon nanotubes (fSWCNTs) and also multiwall CNTs (fMWCNTs) with PBT/PTMO, a block copolymer of semicrystalline poly(butyl terephthalate) (PBT) with amorphous oxytetramethylene (PTMO). For both single wall (SW) and multiwall (MW) carbon nanotubes (CNTs) tensile modulus and strain at break as a function of CNTs’ concentration (cCNT) show maxima. Elongation at break is enhanced by the nanotubes, a plasticizing effect—much stronger for SWCNTs because they have less contact points per unit area with the matrix and also are more flexible. Repetitive tensile tests were also performed; each loading cycle resulted in lowering the tensile modulus. Brittleness B(cCNT) diagrams show minima. New results for CNT hybrids fit an earlier general diagram for determination of viscoelastic recovery in sliding wear (f) as a function of brittleness (B); the original equation with unchanged parameters covers also these results. Volumetric wear was determined after abrasion on a pin-on-disk tribometer. Minima are seen on the volumetric wear versus cCNT diagrams, similar to those on the B(cCNT) diagrams.
Microscratch tests were carried out on polyamide (PA) and polypropylene (PP) by Berkovich indenter to study influence of sliding velocity on microscratch response of carbohydrate polymers. Both penetration depth and residual depth decrease nonlinearly with the increase of sliding velocity. Elastic deformation is dominant in the total deformation during scratching of polymers. Both residual and contact scratch widths decrease nonlinearly with sliding velocity. The elastic recovery rate increases with sliding velocity. Both scratch hardness and lateral hardness increase nonlinearly with sliding velocity. Scratch hardness also increases nonlinearly with the increase of strain rate due to strain rate hardening effect. Scratch friction coefficient of PA decreases with increasing sliding velocities, and can be regarded to be constant under large sliding velocities. Nevertheless, scratch friction coefficient of PP increases with sliding velocity. Residual scratch grooves, scratch friction coefficient, and lateral force under different sliding velocities can be used to reveal the different friction mechanisms of PA and PP.
