Expert Test Services
The correct preload force is crucial for ensuring that bolted joints work and stay secure long-term. We measure preload force in our lab or on-site to ensure that your bolted joint remains safe throughout its life cycle.
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 assembly tools used. Consequently, the generated preloads vary a great deal during the assembly process. By measuring the preload force ultrasonically, we can gauge the preload force that is actually present when the bolt is installed.
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, first in its initial unloaded state, 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 it 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 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 does not 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.
As experts in fastening and materials technology, we measure ultrasonic preload force 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.
Read our related white papers to learn more about the preload force in the bolted joint, what you need to pay attention to so your bolted joints don’t loosen, and how to calculate bolted joints correctly:
White Paper
We have all experienced it: screws or nuts are loosening, whether on a bicycle or a pair of glasses. So, what is the cause of this? And how do we prevent this? Learn more.
VDI 2230
Design your product with a focus on fastening joints from scratch. To ensure the quality and safety of your bolted joints, the guideline VDI 2230 provides you the highest standards. Learn more.
As experts in fastening and materials technology, we conduct a wide range of tests in our technical laboratories to support your quality assurance.
