Friction and wear studies of some PEEK materials

The friction and wear behavior of several types of PEEK polymers and composites were studied. The influence of carbon fiber, lubricant and thermally conductive fillers were evaluated, as well as the effects of contact load and temperature.  The tests were done using a reciprocating ball-on-disc set-up. The materials were tested under the load of 5 N and 15 N, at room temperature, 80°C, 120°C and 150°C. The difference between the materials was substantial, with a friction coefficient varying between 0.03 and 0.3 for the different materials at 120°C. PEEK with carbon fiber filler showed an improvement in both friction and wear compared to unfilled PEEK. When adding lubricant, PTFE, to the composite the friction and wear were improved even more. PEEK with thermally conductive filler on the other hand had both highest friction and wear. Increasing the temperature slightly decreased both friction and wear for most of the PEEK materials. At 150°C, only the composite with PTFE lubricant had a low friction and wear

Rolling Fatigue Life of PM Steel : Influence of Sintering Temperature and Powder Particle Size

In the present study, a lean PM steel was tested for rolling contact fatigue. Medium density PM steel (7.15 g/cm3) sintered at two different temperatures and with two different initial powder sizedistributions was tested. Image analysis was performed on LOM images of cross sections to revealthe microstructure and morphology. Image analysis revealed that a smaller initial powder sizedistribution results in smaller pores and that a higher sintering temperature results in pores that aremore circular. Materials sintered at high temperature with smaller initial powder size significantlyoutperformed the others when tested for rolling contact fatigue, indicating that smaller and morecircular pores are beneficial for the survival of the material. Cracks were found to initiate at pore edgesand propagates trans- as well as intergranular at about the depth below the surface corresponding tothe largest von Mises stress.

Rolling Fatigue Life of PM Steel : Influence of Sintering Temperature and Powder Particle Size

In the present study, a lean PM steel was tested for rolling contact fatigue. Medium density PM steel (7.15 g/cm3) sintered at two different temperatures and with two different initial powder sizedistributions was tested. Image analysis was performed on LOM images of cross sections to revealthe microstructure and morphology. Image analysis revealed that a smaller initial powder sizedistribution results in smaller pores and that a higher sintering temperature results in pores that aremore circular. Materials sintered at high temperature with smaller initial powder size significantlyoutperformed the others when tested for rolling contact fatigue, indicating that smaller and morecircular pores are beneficial for the survival of the material. Cracks were found to initiate at pore edgesand propagates trans- as well as intergranular at about the depth below the surface corresponding tothe largest von Mises stress.

Rolling fatigue life of PM steel with different porosity and surface finish

Gears made of PM steel are of interest for the automotive industry because they can be produced to near net shape with only a few processing steps. Automotive gears experience a complex contact situation with rolling as well as combined rolling and sliding. They also have to be able to withstand high loads and fairly high temperature variations. Earlier work show that the main limiting parameter of the contact fatigue life of PM steel is the porosity. A higher porosity/lower density will decrease the fatigue life of the PM component. In the present study, the pure rolling contact fatigue life of PM steel with different density and surface finish has been investigated. A rolling contact fatigue test rig, where rods of the tested material are mounted between two rolling wheels, was used. Two densities of PM steel, 6.8 and 7.15 g/cm(3) and a full density reference steel with two different surface finishes, centerless grinded and superfinished, were tested. The tests were run for a given number of load cycles or until failure (fatigue life). SEM was used to study the surfaces and cross-sections to reveal the mechanisms of crack initiation and propagation. The higher density PM steel (7.15 g/cm(3)) outperformed the lower density steel (6.18 g/cm(3)) by a factor of around 4 in fatigue life at the same surface pressure, regardless of surface finish. Cracks are initiated at a depth of around 100 mu m. These cracks propagate and eventually they reach the surface, causing surface damage and failure. For the low density PM steel, both sub surface crack initiation and failure occurred earlier (at a lower number of load cycles) than for the higher density PM steel. Severe surface damage or wear were not found until failure occurred. Still, some initial alteration of the surfaces was seen already after 0.5 million load cycles, in the form of removal of the highest asperity peaks on the centerless grinded surfaces, and opening of the surface pores on the superfinished surface. No effect of surface finish was found on the fatigue life. The difference in surface roughness could induce a difference in local stress concentrations at the surface, but in this test the cracks causing fatigue failure are initiated at a depth where the stress distribution is not affected by local surface stress concentrations. This means that for fairly smooth surfaces roughness, the surface of PM steel is not important when it comes to pure rolling fatigue life

Ingenjörsutbildningar vid Uppsala universitet. Studenter granskar några utbildningar ur genusperspektiv

Från september 2007 till maj 2008 genomfördes ett projekt på Teknisk-naturvetenskapliga fakulteten vid Uppsala universitet, där studenter granskade några tekniska utbildningar ur genusperspektiv.Syftet med granskningen var att upptäcka eventuella strukturer som skulle kunna utgöra hinder för kvinnliga studenter, samt att få en kunskapsbas för ett förbättringsarbete. De utbildningar som ingick var civilingenjörsprogrammen i Teknisk fysik, System i teknik och samhälle och Kemiteknik, vilka utgör tre av totalt nio civilingenjörsprogram och har olika andel kvinnliga studenter. Avsikten var att även granska ett av tre högskoleingenjörsprogram vid fakulteten, men programmet utgick i brist på granskare. Totalt deltog femton studenter från årskurserna två och tre, varav åtta kvinnliga studenter och sju manliga, som granskare. De granskade föreläsningar, lektioner, laborationer och seminarier, och tittade även på studiemiljön, och kvinnliga och manliga förebilder. Bland lärare och handledare såg granskarna prov på både genusmedveten pedagogik och besvärande stereotypa könsuppfattningar. Bristen på kvinnliga förebilder vad gäller föreläsare, lektionsledare,handledare och författare till kurslitteratur var stor. It/datorer och deras användande upplevdes vara en manlig domän. Laborationer utmärktes av att studenterna fritt valde grupper och då oftast jobbade i könsuppdelade grupper och med samma personer hela tiden. Möjligen fick kvinnliga studenter mer hjälp på gott och ont. Ett par av granskarnas förbättringsförslag, utöver fler kvinnliga förebilder, var obligatorisk utbildning i genusmedveten pedagogik för alla lärare, mer aktiverande undervisningsformer, en genusutbildning för alla studenter och återkommande uppföljningar av dessa aktiviteter. Granskarna rapporterade också om tysta studenter och låg grad av interaktion och aktiverande pedagogik. Utöver granskningsresultaten och förslagen på förbättringar, har projektet lett till en ökad genusmedvetenhet hos de deltagande studenterna. Metoden att använda studenter som granskare har fungerat bra och kan prövas inom fler områden. Projektet har också gett projektgruppen en ökad insikt i studenternas vardag

The influence from PTFE on surface and sub-surface damages of glass fiber reinforced PPS

Polymer composites are common materials for tribological components, even at relatively high operating temperatures. One advantage is the possibility to add low friction additives, such as PTFE, to the base material. In this paper the influence of such additives was studied, with focus on surface and sub-surface damages. The polymer composites were PPS with glass fibers (PPS-F), PPS with glass fibers and PTFE (PPS-L) and PEEK with carbon fibers, graphite and PTFE (PEEK-L). A reciprocating ball-on-disc test set-up, with ball bearing steel balls as counter material, was used with 5 N and 15 N normal load. The tests were run for 2,000 and 10,000 cycles in room temperature, 80 °C and 120 °C. PPS-F showed high friction (µ ≈ 0.4–0.5) and severe surface damage of both the polymer and the counter surface. Sub-surface cracks, detachment of fibers from the polymer and a deformed surface layer was revealed, when studied in cross section. The load and temperature had negligible effect on the friction, however a higher temperature resulted in more surface damage of the PPS-F. PPS-L and PEEK-L showed relatively low friction (µ ≈ 0.1) and superficial surface damage. XPS analysis revealed a thin tribofilm of PTFE in the wear track for PPS-L

Semi in-situ measurement of microstructural changes in PM steel during indentation

In the present study, microstructural changes of sintered steel under compressive load are studied by a novel method. The aim is to gain further understanding of how the pores and microstructure react to different loads, which is of interest for surface densification of PM steels. Images of polished cross-sections are acquired before and after Brinell-indentation. Distinct features of the before and after images are matched using image registration, revealing the microstructural changes underneath the surface of the PM steel due to plastic deformation by the indentation. The method is reliable and provides accurate measurement of microstructural changes providing data that will broaden the understanding of how the microstructure is altered at loads above the yield limit

Semi in-situ measurement of microstructural changes in PM steel during indentation

In the present study, microstructural changes of sintered steel under compressive load are studied by a novel method. The aim is to gain further understanding of how the pores and microstructure react to different loads, which is of interest for surface densification of PM steels. Images of polished cross-sections are acquired before and after Brinell-indentation. Distinct features of the before and after images are matched using image registration, revealing the microstructural changes underneath the surface of the PM steel due to plastic deformation by the indentation. The method is reliable and provides accurate measurement of microstructural changes providing data that will broaden the understanding of how the microstructure is altered at loads above the yield limit