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In the last years, new and precise tightening methods have been introduced in the automotive industry with the purpose of reaching high-precision and low-scatter assembly force. In general, these methods are based on measurement of the angular displacement of a bolt head or nut taking into consideration a fixed reference. The attainment of maximum precision assembly x pre-load is reached at time fasteners are tightened in the elastic-plastic zone, i.e. under permanent deformation. In some applications fasteners are tightened more than once thus resulting in increase in the plastic deformation that add up after each tightening. The purpose of present study is to demonstrate behavior (plastic deformation in 8.8 and 10.9 high strength bolts) whenever bolts are submitted to assembly forces up to 100% of their capability to generate assembly x pre-load, using these results to establish bolting parameters and adequate number of reutilization.

General Motors Corporation has always made every effort so that our end products and processes and configuration of components could help preserve the environment. Along those lines, General Motors do Brasil started to develop a protective coating that is corrosion resistant and environment friendly. At first, this will be used for fasteners. This effort involves dramatic changes in attitude, such as our need to admit that we are responsible for managing resources and keeping our world habitable and healthy for the future generations. This study describes metallic and organometallic coatings with an increased resistance to corrosion associated to temperature, free of such harmful metals as cadmium, nickel, lead, chromium, etc. Also demonstrated here is the significance of the total friction coefficient and its composition, considering the friction coefficients inherent to the fastener threads/heads.