Improved Mechanical Preload Measurement of Bolted Joints for Light Weight Design With CFRP Components

Bolted joints are widely used in the automotive industry. New requirements in terms of lightweight design and the use of fiber reinforced plastics need revised design guidelines. The preload of a bolted joint is crucial for monitoring its performance and condition. This paper gives an overview of common methods for preload measurement and focuses on techniques which deal with the specific need in R&D. Two systems, based on a mechanical length measurement of the bolt are described in detail. One system uses a conventional micrometer spindle and the other system a precise length gauge. Sources of errors are discussed and the most significant factors to achieve a precise measurement are given. In summary, the preload measurement by a mechanical length measurement, either with a micrometer spindle or with a length gauge, is easy to handle and enables to receive accurate results in R&D.