Today new automotive engine design is optimized in terms of mass. However, in terms of structural stiffness, optimizations mainly consider eigenfrequency criteria. But in assembly components with very low stiffness, cumulated microslip phenomena can occur when the structures are subject to cyclic loadings. In time and after a large number of cycles, macro-displacements can be observed between assembly components and then assembly failures will occur. Bush, plain bearing, roller bearing in conrod or in gearbox can be subject to this kind of problem.
In this paper, after a short description of various mechanisms which can cause microreptation phenomena, two types of cumulated microslip occurring in the engine and the gearbox are presented. Behavior specificities will be highlighted to remind how unusual cumulated microslips are. Based on field data, it appears that the probability of both phenomena occurring is extremely low. This implies that it is not appropriate to use devices concerned by this problem in order to reproduce and to investigate the phenomenon. Moreover, to assess the phenomenon sensitivity with respect to certain parameters, it follows that specific test rigs have to be developed. To cope with the problem for gearbox and conrod, two specific test rigs have been designed and finalized. Their schematic description will allow to assess the delicate points of the tests.
Some results obtained on test rigs are detailed and demonstrate that the mechanical behavior of cumulated microslip is quite complex. Friction phenomena in interface assembly appear to be a key characteristic. For example, significant friction variations with respect to time and slip displacement have been observed.