178 research outputs found
Evaluation of the real contact area in three-body dry friction by micro-thermal analysis
Many tribological properties and wear mechanisms occurring on the micro-and nanoscale are strongly controlled by the so-called real contact area (Ar) which is a small fraction of the nominal or apparent contact area (Aa). The determination of Ar is often based on either (i) a geometrical approach describing the real geometry of contacting surfaces or (ii) a mechanical approach involving contact mechanics and physical-mechanical properties. In addition some experimental methods have also been attempted but they generally do not take into account the presence of third body at the interface—i.e. the wear debris trapped within the contact. In this paper we propose an experimental approach to estimate the dynamic real contact area from the operating parameters (Fn, v, T) and the tribological responses (μ, Ft) in presence of third body. A scanning thermal microscope (SThM) is used for determining both the thermal conductivity of the third body and the relationship between the contact temperature and the thermal power really dissipated at the micro-asperity level. These results are combined with a thermal model of the macro-tribocontact for computing the real contact area and the real contact pressure. Validation of these results is carried out using a classical Greenwood Williamson model and finite element models built from the real AFM maps
A multiscale tribological study of nacre : Evidence of wear nanomechanisms controlled by the frictional dissipated power
Sheet nacre is a hybrid biocomposite with a multiscale structure, including nanograins of CaCO3 (97% wt.% – 40 nm in size) and two organic matrices: (i) the “interlamellar” mainly composed of β-chitin and proteins, and (ii) the “intracrystalline” mainly composed by silk-fibroin-like proteins. This material is currently studied as small prostheses with its tribological behaviour. In this work, the latter is studied by varying the frictional dissipated power from few nW to several hundreds mW, in order to study the various responses of the different nacre’s components, independently. Results reveal various dissipative mechanisms vs. dissipated frictional power: organic thin film lubrication, tablet’s elastoplastic deformations, stick-slip phenomenon and/or multiscale wear processes, including various thermo-mechanical processes (i.e., mineral phase transformation, organics melting and friction-induced nanoshocks process on a large range). All these mechanisms are controlled by the multiscale structure of nacre – and especially by its both matrices and respective orientation vs. the sliding direction
Triboactive surfaces in multi-asperity nanotribology
In this work, n-octadecyltrichlorosilane (OTS) have been grafted on various micro-pillars created by Deep Reactive-Ion Etching (DRIE) of silicon wafers. This multi-architectured surfaces have then been tested with a ball-on-disc nanotribometer CSM Instruments (Fn: 3 mN, ball: Si3N4 1,5 mm) working in linear reciprocating mode, under various environmental conditions. Whereas the pillar's height is always fixed at 10 μm, their shapes and pitches are changed in order to test various wettability models – as Cassie-Baxter or Wenzel ones [4]. The Cassie-Baxter model can be applied in the densest pillars' area while the Wenzel one matches with weakest pillar's area. Since the frictional behavior of OTS monolayers is known to be thermally sensitive, the temperature of the structure is imposed during the tribological test by using a Peltier module
Titanium oxynitride thin films sputter deposited by the reactive gas pulsing process
International audienc
Development of a new nanotribometer with multi asperity contact.
International audienceIt is often difficult to make a connection between the tribological properties really assessed for a single asperity and the ones which involve the whole asperities in a microcontact. We propose a new apparatus development based on passive diamagnetic levitation (PDL) that can be used to study friction in microcontact with a lower range of force than with classical nanotribometers. This sensor measures micro and nanoforces. Its sensitive part is a ten centimeters long glass capillary tube used as a horizontal levitating seismic mass (20 to 80 mg). This rigid part is connected to a magnetic spring with stiffness between 0.01 and 0.03 N/m. The measurement range is 100ÎĽN with a resolution between one and five nanonewton. In order to validate this sensor in a multi asperity nanotribological context, this part is used to measure tangential friction forces generated by spherical micro-objects sliding on flat substrate. Results are compared with the ones provided by a classical multiasperity nanotribometer
Influence of substrate temperature on titanium oxynitride thin films prepared by reactive sputtering
Heat Treated NiP–SiC Composite Coatings: Elaboration and Tribocorrosion Behaviour in NaCl Solution
Tribocorrosion behaviour of heat-treated NiP and NiP–SiC composite coatings was investigated in a 0.6 M NaCl solution. The tribocorrosion tests were performed in a linear sliding tribometer with an electrochemical cell interface. It was analyzed the influence of SiC particles dispersion in the NiP matrix on current density developed, on coefficient of friction and on wear volume loss. The results showed that NiP–SiC composite coatings had a lower wear volume loss compared to NiP coatings. However, the incorporation of SiC particles into the metallic matrix affects the current density developed by the system during the tribocorrosion test. It was verified that not only the volume of co-deposited particles (SiC vol.%) but also the number of SiC particles per coating area unit (and consequently the SiC particles size) have made influence on the tribocorrosion behaviour of NiP–SiC composite coatings
Influence of substrate temperature on titanium oxynitride thin films prepared by reactive sputtering
- …