| 1. |
- Khan, Sharjeel Ahmed, et al.
(author)
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A comparative study in the tribological behaviour of different DLC coatings sliding against titanium alloys
- 2024
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In: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 554-555
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Journal article (peer-reviewed)abstract
- In this study, the tribological behaviour of different Diamond-like-Carbon (DLC) coatings sliding against titanium alloy (Ti6Al4V) was analysed in a pin-on-disc tribometer at different applied loads to study effectiveness of tool coatings in titanium alloys machining. Three different DLC coatings were deposited on cemented carbide substrate using HiPIMS (DLC-Ar, DLC-Ne) and arc (DLC-Bn) deposition techniques. A detailed analysis of the wear track and titanium countersurfaces were performed following the tribotest to develop understanding about the wear mechanism and associated variation in the friction response. The results indicated that DLC-Ar presents low friction and reduced wear of coating and respective titanium countersurface at lowest load, seemingly due to its inherent tendency to spontaneously form graphitic transfer-layer at the interface. With an increase in the applied load, the tendency to retain tribofilm decreases as shearing ensue quickly exposing the underneath substrate material. The wear performance of DLC-Ne coatings is better than DLC-Ar under highest load and friction behaviour relatively close to DLC-Ar coatings. In comparison, under increased applied loads, DLC-Bn coatings offered better wear resistance and low friction compared with DLC-Ne and DLC-Ar coatings, which would offer improved performance in machining of titanium alloys.
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| 2. |
- Khan, Sharjeel Ahmed, et al.
(author)
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Custom-tailored cross-cylinder tribotest to emulate wear mechanism in drilling of CFRP-Ti stacks
- 2023
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In: Tribology International. - : Elsevier. - 0301-679X .- 1879-2464. ; 186
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Journal article (peer-reviewed)abstract
- While drilling of CFRP-Ti stacks, tool experiences complex tribomechanical interaction due to dissimilar workpiece constituents. For emulating tool wear behavior, the typical tribotest configuration such as reciprocating and pin-on-disc test are not representative for imitating contact scenario underwent during the drilling operation. Cross-cylinder tribotest is an effective test configuration to emulate contact in different manufacturing processes by providing fresh contact surface during sliding. In this work, for the first-time, tool wear of WC-Co cylinders was analyzed in cross-cylinder configuration against multi-material stack arrangement. Moreover, cross-cylinder testing against multi-material [CFRP-Ti]n workpiece showed cyclic variation in coefficient of friction against different workpiece constituents and wear mechanism is a combination of adhesive and abrasive wear on WC-Co tool, comparable to actual drilling operation.
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| 4. |
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| 5. |
- Khan, Sharjeel Ahmed, et al.
(author)
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Surface Roughness Influence on Tribological Behavior of HiPIMS DLC Coatings
- 2023
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In: Tribology Transactions. - : Taylor & Francis. - 1040-2004 .- 1547-397X. ; 66:3, s. 565-575
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Journal article (peer-reviewed)abstract
- The application of diamond-like carbon (DLC) coatings in dry machining of difficult-to-machine materials has been gaining popularity due to high inertness, low coefficient of friction (COF), and high hardness of these coatings. Although the effect of surface roughness on the tribological properties of DLC coatings is of paramount importance, usually it is overlooked and coatings performance analysis was accomplished generally on highly polished substrates. The generation of polished surfaces is a time-consuming, labor-intensive process and, in most cases, not feasible for the industry due to its high cost. This article focuses on determining the effect of substrate (cemented carbide, WC-Co) surface roughness on the load-bearing capacity and tribological properties of DLC coatings deposited by High Power Impulse Magnetron Sputtering (HiPIMS) in Ne–Ar gas plasma. The DLC films were deposited onto WC-Co substrates with three different surface roughness profiles and their tribological performance were evaluated using a reciprocating tribotest. The high surface roughness resulted in increased wear rate due to high levels of asperities and increased potential for premature delamination of the coatings, while also causing severe damage to the counterbody due to inhibition of transfer film formation.
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| 7. |
- Moran, M. Carmen, et al.
(author)
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Mixed Protein Carriers for Modulating DNA Release
- 2009
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:17, s. 10263-10270
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Journal article (peer-reviewed)abstract
- Aqueous mixtures of oppositely charged polyelectrolytes undergo associative phase separation, resulting in coacervation, gelation, or precipitation. This phenomenon has been exploited in forming DNA gel particles by interfacial diffusion. We report here the formation of DNA gel particles by mixing solutions of double-stranded DNA with aqueous solutions containing two cationic proteins, lysozyme and protamine sulfate. The effect of the lysozyme/protamine ratio on the degree of DNA entrapment, surface morphology, swelling-deswelling behavior, and kinetics of DNA release has been investigated. By mixing the two proteins, we obtain particles that display higher loading efficiency and loading capacity values, in comparison to those obtained in single-protein systems. Examination of the release profiles has shown that in mixed protein particles, complex, dual-stage release kinetics is obtained. The overall release profile is dependent on the lysozyme/protamine ratio. The obtained profiles, or segments of them, are accuratelly fitted using the zero-order and first-order models, and the Weibull function. Fluorescence microscopy studies have suggested that the formation of these particles is associated with the conservation of the secondary structure of DNA. This study presents a new platform for controlled release of DNA from DNA gel particles Conned by interfacial diffusion.
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| 9. |
- Nikonovich, Maksim, et al.
(author)
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Effect of cryogenic aging and test-environment on the tribological and mechanical properties of PEEK composites
- 2024
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In: Tribology International. - : Elsevier Ltd. - 0301-679X .- 1879-2464. ; 194
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Journal article (peer-reviewed)abstract
- This study investigated mechanical and tribological properties of polyetheretherketone (PEEK) and PEEK composites, before and after aging in liquid nitrogen for 5 months. Tribological tests conducted at 25 °C and at − 100 °C in air and in high vacuum (10−5 Pa) environment revealed the effect of matrix modification, fillers, environment, temperature, and cryogenic aging on their performances. Cryogenic aging of the polymers resulted in cryogenic embrittlement and decrease of the fracture toughness by around 10% and increase of wear rate by at least 20%. Very low coefficient of friction (0.02) was achieved in cryogenic vacuum environment for carbon fiber, graphite, and PTFE reinforced PEEK. The results indicate the significant impact of aging, temperature and environment on PEEK and its composites.
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| 10. |
- Nikonovich, Maksim, et al.
(author)
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Impact of test-environment and cryogenic aging on mechanical properties and tribological performance of PI-based materials
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Other publication (other academic/artistic)abstract
- This study investigates the effect of test-environment, temperature, and cryogenic aging in liquid nitrogen for 5 months on mechanical and tribological performance of polyimide (PI) and PI composites. Tribological tests were conducted at 25 °C in air, and at both 25 °C and -100 °C in a high vacuum (10-5 Pa) environment. Impact of cryogenic aging, testing condition on PI-based materials varied depending on the polymer structure and composition. Cryogenic aging led to embrittlement, increasing the coefficient of friction and wear rate up to 77% and 165%, respectively. Some polyimides exhibited the lowest coefficient of friction (0.04) in vacuum at 25°C, while the temperature reduction to -100 oC in vacuum generally decreased the tribological performance, increased contact stresses and abrasive wear of the materials.
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| 11. |
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| 12. |
- Nikonovich, Maksim, et al.
(author)
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Structural, thermal, and mechanical characterisation of PEEK-based composites in cryogenic temperature
- 2023
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In: Polymer testing. - : Elsevier. - 0142-9418 .- 1873-2348. ; 125
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Journal article (peer-reviewed)abstract
- Thermal, thermo-mechanical and mechanical properties of four different commercially available polyetheretherketones (PEEK) based materials were investigated. PEEK matrix was either modified and/or reinforced with carbon fibres, graphite and/or PTFE. Impact strength was measured at three different temperatures: 25 °C, −100 °C, and −195 °C. At 25 °C, thermal stability and mechanical properties, including the elastic modulus, compression, and impact strength, were enhanced with the addition of carbon fibres. Matrix modification had a minor impact on thermal stability, while the mechanical properties decreased, except for impact strength. At −100 °C, the mechanical properties of the neat polymers were improved, including increased impact strength by 20% compared to values at 25 °C. Addition of fillers hindered the rise of impact strength due to complex mechanisms caused by different coefficients of thermal expansion of reinforcements and matrix. At −195 °C, the significant increase of impact strength was revealed for unmodified PEEK reaching 30 times higher values than at 25 °C, while matrix modification suppressed the rise of impact strength. The scratch test indicated the superior behaviour of unfilled PEEK during the tested load range (up to 15 N), while the effect of the fillers was observed at much lower load threshold of 7 N.
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| 14. |
- Rezende de Jesus, Rainde Naiara, et al.
(author)
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Interfacial biomechanical properties of a dual acid-etched versus a chemically modified hydrophilic dual acid-etched implant surface : an experimental study in Beagles
- 2018
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In: International Journal of Implant Dentistry. - : Springer. - 2198-4034. ; 4:28
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Journal article (peer-reviewed)abstract
- Background: The high survival and clinical success rates of osseointegration are requisites for establishing a long-term biomechanical fixation and load-bearing potential of endosseous oral implants. The objective of this preclinical animal study was to evaluate the effect of surface microtopography and chemistry on the early stages of biomechanical rigidity with a sandblasted, dual acid-etched surface, with or without an additional chemical modification (SAE-HD and SAE, respectively), in tibia of Beagle dogs. Methods: Two pairs of implants, with the same macrogeometry but different surface technology a) dual acid-etched surface treatment with hydrochloric and sulfuric acid followed by microwave treatment and insertion in isotonic saline solution to increase hydrophilicity (SAE-HD) (test, n = 12); b) dual acid-etched surface (SAE) (control, n = 12) were installed bilaterally in the proximal tibia of six Beagle dogs. In order to determine the effect of surface modification on biomechanical fixation, a test protocol was established to assess the torque and a complete set of intrinsic properties. Maximum removal torque (in N.cm) was the primary outcome measure, while connection stiffness (N.cm/rad) and removal energy (x10-2J) were the secondary outcome measures, and were assessed after 2 and 4 weeks in vivo. A general linear statistical model was used and performed for significant differences with the One-way ANOVA followed by Tukey post-hoc test (P < 0.05). Results: The removal torque values did not reveal significant statistical differences between SAE-HD and SAE implants at any observation times (P = 0.06). Although a slight increase over time could be observed in both test and control groups. SAE-HD showed higher removal energy at 4 weeks (999.35 ± 924.94 x10-2 J) compared to 2 weeks (421.94 ± 450.58 x10-2 J), while SAE displayed lower values at the respective healing periods (P = 0.16). Regarding connection stiffness, there were no significant statistical differences neither within the groups nor over time. There was a strong, positive monotonic correlation between removal torque and removal energy (= 0.722, n = 19, P < 0.001). Conclusions: In this study, no significant differences were observed between the specific hydrophilic (SAE-HD) and hydrophobic (SAE) surfaces evaluated, in terms of biomechanical properties during the early osseointegration period.
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