In recent years, self-loosening detail mechanisms of bolted joints had been revealed using three dimensional FE analysis in which the bolts and the nuts have almost perfect configurations geometrically. However the configurations of actual bolts and nuts have certainly errors. Wear on contact surfaces also occurs in the actual bolted joint. Hence it is not easy to accurately simulate the actual bolted joint by only FEM. In this study, an influence of lubricants on self-loosening characteristics have been investigated in order to understand actual phenomena in self-loosening process. The self-loosening tests for a hexagon head cap screw M10 due to transverse vibration were performed under lubricated conditions by Machine oil ISO VG46, Molybdenum disulfide grease and Polyisobuthylene which is used as a special lubricant for bolt tightening. A bearing surface configuration of the bolt was controlled in this study. The results showed that the bolted joints lubricated by Polyisobuthylene had a higher resistance for self-loosening than the bolted joints lubricated by Molybdenum disulfide grease and Machine oil ISO VG46. The number of cycle until loosening depended on bearing surface configurations.
Precise calculation of sealing pressure profile around cylinder bore is essential for the multi-layer-steel(MLS) engine cylinder head gasket design. This paper describes 2D finite element analysis of MLS head gasket taking into consideration of rubber coating model in which coating is expressed by means of hyper-elastic model and measured frictional coefficient is used as contact boundary condition. Modeling of the rubber coating of MLS is a key of the simulation. Two typical head gasket structures, inner-shim type and grommet type, are examined in this paper. The calculation results showed good agreement with pressure-sensitive paper measurement of both types of the gasket. Same modeling methodology is applied to assess a restraining force of a head gasket against a displacement of cylinder bore wall of open-deck aluminum cylinder block. The result illustrates that head gasket restraining force differs in head gasket structure and has a peak according to cylinder inner pressure. The restraining force peak is caused by the change of contact condition, from stick area to slip of rubber coating. The modeling methodology described in this paper provides a powerful simulation tool for the cylinder head gasket and engine structure design.
In our previous study, microstructure and mechanical properties of diamond-like carbon (DLC) films prepared by plasma based ion implantation and deposition using toluene (C7H8) as a source gas were investigated. It was reported that G-peak full width at half maximum [FWHM(G)] shows a maximum value at a G-peak position of around 1540 cm-1, indicating structural changes of DLC films; polymer-like (PLC) to diamond-like carbon (DLC) structure in lower wavenumbers than 1540 cm-1 and diamond-like to graphite-like carbon (GLC) structure in higher wavenumbers than 1540 cm-1. Further, two linear relationship between mechanical properties and FWHM(G) were observed depending on the microstructure of DLC films. In this study, we report the dependence of source gases, methane (CH4), acetylene (C2H2) and toluene, on the microstructure of DLC films, and the correlation between microstructure and mechanical properties of DLC films. It was found that FWHM(G) shows a maximum at a G-peak position of around 1540 cm-1 regardless of source gases. Furthermore, there exists a linear relationship between PL background component and hydrogen content of the films, that is, hydrogen content can be estimated by a simple equation regardless of source gases. The correlation of hardness with FWHM(G) of DLC films prepared using CH4 and C2H2 gas shows good agreement with the correlation line of DLC-GLC provided in the case of C7H8.