Proceedings of SerbiaTrib '13

contact’s conformity [18] they obtain the hardness,the deformability value (index) (which describesthe coarse surfaces’ deformation properties), aswell as the elasticity module for organic polymerspolymethylmethacrylate – PMMA; polystyrene –PS; polycarbonate – PC, ultra high molecularweight polyethylene – UHMWPE. We alsodescribe the dependence of the imposed penetrationdepth, the maximum load and the straining speed,the hardness and the elastic modulus [18-22]. Thetypical penetrating depths are included within theapproximate 10 nm to 10 μm range, whilst theapplied loads are smaller than 300 mN.We can observe the fact that almost withoutexception, the ploughing is accompanied byadhesion and in certain conditions it may lead tomicro-cutting, which represents a supplementaryadding to increase the friction force.There are other mechanisms to dissipate theenergy while straining. For instance, whenever apolymer with viscous-elastic reaction slides on ahard surface, the energy dissipation is caused by thehigh losses through hysteresis. This strainingcomponent is known under the name of friction dueto elastic hysteresis [1]. The energy can, as well, betransported further, for instance through elasticwaves generated at the interface and coming out atinfinit, as, a nucleation and micro-cracksdevelopment within the material, consequence [20].The mechanical component consists in theresistance of the softer material to harder asperities’ploughing. The adhesion component comes of theadhesion links formed between the surfaces duringthe friction contact. We believe that for polymersthe adhesion molecular component exceeds by farthe mechanical one [20], and we can explain itthrough the generated films’ transfer on the metalcounter-face. The following factors considerablyaffect the friction force: the contact load, slidingspeed and temperature. The effects are notindependent. For instance, according to the contactload and contact speed, the temperature mayconsiderably vary, changing the friction mode [21].2. MATERIALS AND METHODSIn order to study the metallic counter-part’swear in dry contact with glass fibres reinforcedplastic materials we use Timken type frictioncouples (with linear contact), cylinder on plan,which allows us to attain high contact pressures,hence high contact temperatures. In this manner wenotice, whether and in which conditions the plasticmaterial transfer on the metallic surface appears, aswell as the influence of the glass fibres fillingduring this phenomenon, and its effect on thesurface’s wear. As we do not follow the polymer’swear, but only the polymer’s friction influence,over the samples’ metallic surfaces wear, we usethe unidirectional sliding movement.We perform the tests using experimentalequipment containing a Timken type linear contactfriction couple, continuously controlling the normaland friction loads, and contact temperature. Theunidirectional movement and the linear contactallow us to attain very high contact pressures andtemperatures. We build the friction couple out of aplastic cylinder Nylonplast AVE polyamide + 30%glass fibres, which rotates at different speedsagainst the polished surface of a steel plan disk.The cylinder has an outer diameter of 22.5 mm and10 mm height.We choose as sample steel disks with 18.2 mmdiameter and 3 mm thickness. We polish the disks’surfaces successively using sandpaper of differentgranulations (200, 400, 600 and 800) and, finally,we polish them on the felt with diamond paste. Weobtain mirror polished surfaces, with roughness R aof 0.05 µm. This metal surface’s quality allows usto eliminate the influence of the metallic surface’sstate on the friction coefficient’s evolution andvisualization, to make measurements using opticalmicroscopy and to accurately record the wear tracesappeared on the metallic surfaces.Fig.1 shows the friction couple (a) and itsinstallation within the experimental equipment (b).(a)Figure 1. Friction couple (a) and its installation in theexperimental equipment (b), where 1 - cylindrical liner;2 – steel disk sample; 3 – nut; 4 – hole; 5 - knife-edge.The friction couple is build out of a cylindricalliner (1) and a plane disk type sample (2). The lineris fixed with the help of a nut (3) on the drivingshaft (4), and the disk sample is placed in a specialhole made within the elastic blade (5). We build thesample disk base in such a manner so that the baseallows the sample to make small rotations aroundthe edge of a knife fixed in the sample’s bezel,perpendicularly on the driving arbour. In this waywe ensure a uniform repartition of the load on theentire linear contact between the liner and steelsample, even if there are small building orassembling imperfections. An electric engine putsthe shaft into a rotation movement using trapezoidaltransmission belts.The experimental device allows us tosimultaneously measure the normal and tangential(b)13 th International Conference on Tribology – Serbiatrib’13 59