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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.

Gasketed bolted joint analysis tools are gaining importance as the market place demands superior product performance, reduced cycle time, and lower cost. Design analysis tools can be used to predict product performance over the life of the joint. Numerous design concepts under a range of operating conditions can be simulated. The optimal designs can be determined before a prototype is manufactured and tested. The reduction in prototyping and testing results in cost savings and a reduction in design time. The customer is provided with a product with superior sealing performance at a lower cost. This paper presents a design analysis technique which uses a non-linear finite element program in conjunction with a spreadsheet. The spreadsheet functions as a user friendly input and output interface to the finite element program. Parametric models are used to define the geometry of standard sealing system components that include gaskets, flanges, and fasteners.

The oil sump sealing performance analysis has been carried out through the analysis of the joint formed by the sump flange, the engine block flange, the gasket, and the bolts. Oil sump flange bending plays a major role in affecting the gasket sealing performance, it is modeled using 3D shell element and reduced to a substructure stiffness matrix for the sealing surface. This reduced stiffness matrix along with the stiffness of the gasket and bolt are used in a 2D plate program to provide detailed gasket pressure profile on the sealing surface. The effect of sump wall height, corner bend, boundary conditions have been studied in detail to make sure that the lowest sealing pressure on the entire flange is at least equal to or larger than the predicted value. The effect of bolt spacing on the sealing pressure has also been studied, the results of which can be used as a guideline for bolt spacing specification in new engine development.

In an integrated noise isolation system, both gasket and bolt isolators play an important role in the resultant total load, contact stress, and system static and dynamic stiffness. One standard approach to design is based on using a shape factor in conjunction with a simple stress-strain relation. This approach can produce reasonable results under small deformation. But the deviation is so large that it is not appropriate to use it for reliable designs under large deformation. Experimental approaches and finite element methods are effective at characterizing the load-deflection relationship of bolt isolators under large compressive deformation. In this paper, a parameter study of a sequence of finite element analyses will be presented and a parametric model will be determined based on the FEA results to best represent the isolator load-deflection behavior under large compression.

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.

The gasket cross section plays an important role in the resultant total load, contact stress, and stiffness of a gasket constructed from elastomeric materials. One standard approach to design is based on using a shape factor in conjunction with a simple stiffness calculation. This approach can produce reasonable results for simple cross-sections under small deformation. In many situations, the complexity of the shape and relatively large deformation prevents this approach from predicting the behavior of the gasket with acceptable accuracy. Experimental approaches and finite element methods are effective at characterizing the stiffness under these conditions. In this paper, a parameter study of the results of a sequence of finite element analyses were used to construct a model of standard gasket cross sections, specifically a triangular beaded cross section. The resulting formula can be used to quickly determine the gasket load-deflection with good accuracy.

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.