Most bolts are designed as tension members, developing a compressive force in a joint (clamp load) that reacts against the external forces of the system: pressure, wind, shock, etc. The main objective of the assembly operation is the creation of the design tension force in the bolt. The degree of success in the assembly process has a direct relationship to the successful operation of the joint system in the field. Until today, the only convenient methods to determine bolt load in the field or on the production floor was to re-apply the tightening tool: wrench or tensioner. The application of the permanent metal/ceramic sputter deposited ultrasonic transducers on large, tension critical fasteners allows for bolt load measurement at any time. This technology delivers ultrasonic direct load measurement while removing all of the inconvenience and variability of conventional ultrasonic techniques. The thin film transducer is small: O̸ 3–5mm, inert, thin (<25um) and permanently attached to the fastener. It is an easy and convenient way to directly measure clamp load in a fastener during production, inspection and in the field: today, tomorrow and next year. The thin-film transducer can be used on a wider range of fastener sizes than possible with conventional hand-held transducers in long-term maintenance applications. The presentation will discuss ultrasonic bolt load measurement theory, and applications with case histories.

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