Solid particle erosion and viscoelastic properties of thermoplastic polyurethanes

The wear resistance of several thermoplastic polyurethanes (TPUs) having different chemical nature and micronscale arrangement of the hard and soft segments has been investigated by means of erosion and abrasion tests. The goal was correlating the erosion performances of the materials to their macroscopic mechanical properties. Unlike conventional tests, such as hardness and tensile measurements, viscoelastic analysis proved to be a valuable tool to study the erosion resistance of TPUs. In particular, a strict correlation was found between the erosion rate and the high-frequency (~10^7 Hz) loss modulus. The latter reflects the actual ability of TPU to dissipate the impact energy of the erodent particles

Mechanical and abrasion wear properties of hydrogenated nitrile butadiene rubber of identical hardness filled with carbon black and silica

The mechanical and abrasive wear properties of a hydrogenated nitrile butadiene rubber filled with 35 part per hundred rubber carbon black or silica with and without silane surface treatment (SI-si and SI, respectively), were investigated. Specimens were subjected to dynamic mechanical thermal analysis (also to study the Payne effect), mechanical (hardness, tensile modulus, ultimate tensile strength and strain, Mullins effect and tear strength), and fracture mechanical (J-integral) tests. The abrasive coefficient of friction and wear (specific wear rate, Ws) of the hydrogenated nitrile butadiene rubbers of identical hardness were measured against abrasive papers of different grit sizes (P600-P5000).The worn surface of the HNBR systems was inspected in scanning electron microscopy and the typical wear mechanisms deduced and discussed. Coefficient of friction did not change with the grit size by contrast to Ws which was markedly reduced with decreasing surface roughness of the abrasive paper. Ws of the compounds did not vary when wearing against P3000 and P5000 abrasive papers, representing mean surface roughness values of 7 and 5  μm, respectively. This was attributed to a change from abrasion to sliding type wear. hydrogenated nitrile butadiene rubber- carbon black outperformed the silica filled versions with respect to Ws though exhibited the highest coefficient of friction. No definite correlation could be found between the abrasive wear and the studied dynamic mechanical thermal analysis and (fracture) mechanical properties. </jats:p

"Ultralow" sliding wear polytetrafluoro ethylene nanocomposites with functionalized graphene

The dry friction and sliding wear behavior of sintered polytetrafluoro ethylene containing various amounts of functionalized graphene were studied in this work. Graphene was incorporated in 0, 0.25, 0.75, 1, 2 and 4 vol.%, respectively. Sliding wear tests were performed in ring(metal)-on-plate(polytetrafluoro ethylene) test rig under ambient temperature setting 1 m/s sliding speed and 1 MPa contact pressure. The dynamic coefficient of friction and specific wear rate (ws) data were determined. Very low coefficient of frictions (0.12–0.14) were measured for polytetrafluoro ethylene containing 2 or 4 vol.% graphene, which was attributed to the formation of a tribofilm on the countersurface. Specific wear rate went through a maximum (peaked at doubling that of the unmodified polytetrafluoro ethylene at about 0.75 vol.% graphene) as a function of graphene content. Ultralow wear rate data in the range of 10−6 mm3/(N.m) were measured for the polytetrafluoro ethylene nanocomposites with 2 and 4 vol.% graphene. This was reasoned by the formation of a robust tribofilm, the development of which was followed by scanning electron microscopy by inspecting the worn surface of polytetrafluoro ethylene nanocomposites and that of the steel ring of the ring(metal)-on-plate(polytetrafluoro ethylene) test rig. Fourier transform infrared spectroscopic results confirmed the formation of carboxyl groups in the tribofilm. They were supposed to react with the functional groups of graphene and to create complexes with the metal countersurface ensuring the tribofilm with high adhesion and cohesion strengths. </jats:p