1995-02-01

Bolt Load Retention Modeling from Creep Performance Data 950485

Composite materials are replacing metals in a variety of engine and transmission components, including covers, manifolds, pumps and housings. In many applications, the cost and complexity of mounting boss inserts can be avoided by understanding composite creep performance and designing bolted joints for adequate bolt load retention.
A lumped element model of a bolted joint is presented. Based on empirical equations describing creep performance, the present model yields equations to predict clamp load retention in bolted joints. Load retention is aided by the elastic compliance in the fastener, and is reduced by creep compliance in the boss and gasket. To ensure adequate load retention, the fastener must provide adequate elastic compliance to compensate for creep in the boss and gasket. The present model provides a means of choosing composite material, process conditions and fastener type based on application clamp load retention requirements.
The creep performance of phenolic composites has been characterized by a method presented in reference (3). The present model has been verified in bolt load retention experiments on prototype phenolic composite pump covers. The model has been implemented in PC software to facilitate design calculations.

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