Friction and wear behaviour of 18 polymers in contact with steel in environments of air and water

18 polymers were characterized with respect to their friction and wear behaviour in contact with steel in environments of air and water. These were six unfilled materials, i.e. polyamide 66 (PA 66), polyoxymethylene (POM), polyethyleneterephthalate (PETP), polyetheretherketone (PEEK), polyphenylenesulphide (PPS) and polyetherimide; also, the same base materials filled with polytetrafluoroethylene (PTFE) or PTFE plus glass fibre were used.\ud \ud Two types of experiments were performed, i.e. measurement of the coefficient of friction f as a function of the contact temperature Tc (¿f;¿Tc diagrams¿), and measurements of friction and wear in 20 h tests. The f¿Tc diagrams were obtained in air; the 20 h tests were performed in air and in water at a temperature of 20 °C. In air the polymers ran against rings of ball-bearing steel (AISI 52100); in water the rings were made of stainless steel (AISI 316).\ud \ud It turned out that in air addition of PTFE was generally beneficial; PA 66, POM, PETP and PEEK, all filled with PTFE, performed exceptionally well (specific wear rates k appreciably lower than 1×10¿15 m3 N¿1 m¿1). In water, however, PTFE did not function at all. Now PA (with or without PTFE), unfilled POM and PETP filled with PTFE and glass fibre met the k<1× 10¿15 m3 N¿1 m¿1 criterion. With a few exceptions, addition of glass fibre produced unfavourable effects, in air as well as in water.\ud \ud The observed phenomena are explained tentatively in terms of polymer structures and transfer and wear mechanisms, whereby special attention is paid to the ratio of friction over strength

Friction of Teflon-S-coated Ti-6Al-4V under conditions of oscillatory relative motion

An extendable prosthesis for implantation in a human leg has been developed. The friction forces during extension of the prosthesis must be low, so a coating of Teflon-S was applied to the sliding surfaces. During walking, damage can occur as a result of oscillatory relative motion. Therefore experiments were performed with an apparatus which simulated this type of motion. It was found that the coefficient of friction reached a maximum value within one million movement cycles. This maximum value of the coefficient of friction increased with decreasing coating thickness. Even at an initial coating thickness of less than 1 μm, coating with Teflon-S was found to be very effective in reducing friction

Advances in imaging of new targets for pharmacological intervention in stroke: real-time tracking of T-cells in the ischaemic brain

Background and purpose: T‐cells may play a role in the evolution of ischaemic damage and repair, but the ability to image these cells in the living brain after a stroke has been limited. We aim to extend the technique of real‐time in situ brain imaging of T‐cells, previously shown in models of immunological diseases, to models of experimental stroke. Experimental approach: Male C57BL6 mice (6–8 weeks) (n= 3) received a total of 2–5 × 106 carboxyfluorescein diacetate succinimidyl ester (CFSE)‐labelled lymphocytes from donor C57BL6 mice via i.v. injection by adoptive transfer. Twenty‐four hours later, recipient mice underwent permanent left distal middle cerebral artery occlusion (MCAO) by electrocoagulation or by sham surgery under isoflurane anaesthesia. Female hCD2‐green fluorescent protein (GFP) transgenic mice that exhibit GFP‐labelled T‐cells underwent MCAO. At 24 or 48 h post‐MCAO, a sagittal brain slice (1500 µm thick) containing cortical branches of the occluded middle cerebral artery (MCA) was dissected and used for multiphoton laser scanning microscopy (MPLSM). Key results: Our results provide direct observations for the first time of dynamic T‐cell behaviour in living brain tissue in real time and herein proved the feasibility of MPLSM for ex vivo live imaging of immune response after experimental stroke. Conclusions and Implications: It is hoped that these advances in the imaging of immune cells will provide information that can be harnessed to a therapeutic advantage

Learning in virtual worlds : Using communities of practice to explain how people learn from play

Although there is interest in the educational potential of online multiplayer games and virtual worlds, there is still little evidence to explain specifically what and how people learn from these environments. This paper addresses this issue by exploring the experiences of couples that play World of Warcraft together. Learning outcomes were identified (involving the management of ludic, social and material resources) along with learning processes, which followed Wenger’s model of participation in Communities of Practice. Comparing this with existing literature suggests that productive comparisons can be drawn with the experiences of distance education students and the social pressures that affect their participation