Tribological Performance of Coated Surfaces

The fundamentals of coating tribology is presented in a generalised holistic approach to friction and wear mechanisms of coated surfaces in dry sliding contacts. It is based on a classification of the tribological contact process into macromechanical, micromechanical, tribochemical contact mechanisms and material transfer. The tribological contact process is dominated by the macromechanical mechanisms, which have been systematically analysed by using four main parameters: the coating-to-substrate hardness relationship, the film thickness, the surface roughness and the debris in the contact. In this paper special attention is given to the microlevel mechanisms, and in particular new techniques for modelling the elastic, plastic and brittle behaviour of the surface by finite element (FEM) computer simulations. The contact condition with a sphere sliding over a plate coated with a very thin hard coating is analysed. A three dimensional FEM model has been developed for calculating the first principal stress distribution in the scratch tester contact of a diamond spherical tip moving with increased load on a 2μm thick titanium nitride (TIN) coated steel surface. The model is comprehensive in that sense that it considers elastic, plastic and fracture behaviour of the contact surfaces. By identifying from a scratch experiment the location of the first crack and using this as input data can the fracture toughness of the coating be determined.     

The component glycerides of soya bean oil and of soya bean oil fractions

Summary The mixed glycerides of soya bean oil consist of nearly 60% of mono-saturated di-unsaturated glycerides and about 40% of tri-unsaturated glycerides; two polyethenoid groups (chiefly linoleic) are present in nearly 70% of the tri-glycerides, but less than 5% contains three in the same triglyceride molecule whilst linolenic groups occur (singly) in not much more than 25% of the soya bean glycerides. Of the soya bean oil glycerides (37%) which remain in solution in acetone at −40°, about 90% contain two polyethenoid groups and about 10% contain all three acid radicals in this form whilst linolenic acid is present (singly) in about 40% of the glycerides; but over 30% of this fraction still contains one saturated acyl group. Such a solvent-separated soya bean oil fraction would thus appear to be considerably less efficient as a drying oil than certain whole oils such as those of rubber seed or candlenut (lumbang), the latter in turn not possessing so great a linolenic acid content and content of linoleo-linoleno-(tri-unsaturated) glycerides as linseed oil itself.     

Flow induced fiber orientation in compression molded glass mat thermoplastics

This study examines how the mechanical properties in GMT are affected by axisymmetric flow during compression molding. Two types of GMT with different architecture are used, swirled mat and short fiber GMT. Tree different grades are tested for each fiber architecture 20, 30, and 40% fiber content by weight. These are in principle the grades of GMT commercially available today. It is found that the flow reduced the tensile strength by 30 to 50% and the tensile modulus up to 30% in the flow direction. The reduction in mechanical properties, which is mainly caused by flow‐induced fiber orientation, is larger at high fiber contents. The study also showed that there is no major difference in behavior between swirled mat and short fiber GMT regarding flow induced fiber orientation.