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An engine cover isolation system consists of a number of components that interact with each other. These components include the gasket, cover, bolts and bolt isolators. The stiffness and damping of this system determines the dynamic motion of the cover. The magnitude of the cyclic bending stress that develops in the capscrew is proportional to the magnitude of the dynamic motion. If the cyclic bending stress exceeds the fatigue strength of the bolt, a fatigue failure will occur. This paper will present an analytical model for predicting the cyclic bending stress on the outer fiber of the bolt in response to the dynamic motions that occur in an isolation system. The impact of bolt stiffness on system stiffness and on dynamic motion will be reviewed. This analytical model has been validated with experimental results and will enable the isolation system designer to avoid bolt fatigue failures.

Gaskets are used to provide sealing in bolted joints that function under a wide range of assembly and loading conditions. Tolerance distributions of the gasket and flange components as well as assembly load variation will cause the gasket sealing stress to vary. In some cases, this variation is significant. In these cases, gasket designs based on nominal dimensions and loads may not function properly unless one or more engine test and design modification cycles are carried out. A probabilistic technique has been developed to evaluate gasket designs under a range of assembly conditions. The output is a prediction of the statistical distribution of key dimensions such as compressed thickness or parameters such as percent compression. Analysis of these distributions can be used to determine the number of occurrences where a gasket design would be expected to function improperly.

The response of a gasketed, bolted joint to an external load is understood to be effected by all components involved in the joint. The analysis involves the equilibrium of the gasket compressive force with the bolt tension force and the forces external to the bolted joint. Geometric compatibility is maintained when the change in the stretch of the bolt caused by an external force is equal to the change in compressed thickness of the gasket. When the flanges are treated as nondeformable, the classical joint diagram analysis indicates that externally applied loads, which unload the gasket, increase bolt tension. In this paper, the effect of flexible flanges is included in the analysis of simple gasketed bolted flanges. The results show that bolt tension response can deviate significantly from the rigid flange behavior. In certain situations where flanges have a relatively high level of flexibility, external joint forces that unload the gasket also unload the bolt.