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Ultrasonic preload force measurement for secure bolted joints

The correct preload force is a decisive factor in ensuring that bolted joints work and remain secure in the long term. It guarantees that two components that are bolted together behave as a single unit. Bossard’s fastening technology experts will take care of measuring the preload force for you in a technical test laboratory or on-site – to keep you on the safe side throughout your bolted joint’s entire life cycle.

What is the purpose of an ultrasonic preload force measurement?

When a bolt is tightened, a preload is generated that is heavily dependent on the relevant friction on the thread and beneath the bolt head or nut bearing area, as well as on the lubrication and the assembly tools used. Consequently, the generated preloads vary a great deal during the assembly process. By measuring the preload force ultrasonically, we can gage the preload force that is actually present when the bolt is installed.

Read our related white papers to learn why the preload force in the bolted joint is an important variable, what you need to pay attention to so your bolted joints don’t loosen, and how to calculate bolted joints correctly:

 

How does ultrasonic preload force measurement work?

A special ultrasonic measuring device can be used to examine changes in a fastener’s length. This involves passing an ultrasonic acoustic signal through a bolt, for example, in its initial unloaded state first of all, then secondly measuring how long it takes the signal to travel back and forth through the bolt. This “reference time” can be determined individually for each fastener and differs depending on the design and material. The bolt is then tightened, and the runtime measurement is repeated on the loaded bolt. Since the bolt has stretched within its elastic range due to the applied mechanical stress, the ultrasonic signal transit time increases accordingly.

By comparing the different runtimes – the time difference – we get an extremely precise measure of the preload force. This measurement method is also advantageous in that it doesn’t need to be carried out in the test laboratory. It can also be performed on-site (i.e. on installed bolts). The reference runtimes of the bolts used must be known and the measuring instrument must be calibrated accordingly for this purpose.

 

Ultrasonic preload force measurement in the Bossard test laboratory

As experts in fastening and materials technology, we perform ultrasonic preload force measurements on original components in our test laboratories for your quality assurance operations. We use state-of-the-art measuring instruments and methods to determine bolted joints’ preload force and, in doing so, help to ensure that your fastening solutions are secure and meet all the requirements they will encounter throughout their entire life cycle.

Bossard has ISO 17025-accredited test laboratories around the world and relies on a certified quality management system according to ISO 9001:2015. Our qualified ultrasonic preload force measurement staff advise and support you with their accumulated expertise and many years of experience.

 

Contact our experts and learn more about Bossard's Expert Test Services. We are happy to hear from you!

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