Ultrasonic Stress Measurement: Application to Preload Assessment on Already Tightened Bolts |
| Journal |
Materials Science Forum (Volumes 524 - 525) |
| Volume |
Residual Stresses VII |
| Edited by |
W. Reimers and S. Quander |
| Pages |
459-464 |
| DOI |
10.4028/www.scientific.net/MSF.524-525.459 |
| Online since |
September, 2006 |
| Authors |
Henri Walaszek, Patrick Bouteille |
| Keywords |
Acoustic Wave, Acoustoelastic Constants, Already Tightened Bolts, Birefringent Method, Bi-Wave Method, Bolt, Compressional Wave, Differential Method, Longitudinal Wave, Mono-Wave Method, Screw, Shear Wave, Tightening Control, Torque Control, Ultrasonic Assessment of Preload, Ultrasonic Method, Ultrasound |
| Abstract |
When a material is under mechanical load, the stresses modify the velocity of acoustic waves. This
consists in acoustoelastic effect. This property can be exploited for stress measurement in the
material itself when the stress concerns the surface of the material, or in the bulk material, as in
bolts.
The ultrasonic bolt tightening control allows knowledge of preload stress in screws. The accuracy
is much better than in the case of torque wrench. In fact, the use of this mechanical-based
measurement equipment leads to uncertainties due to random resistant torques, induced by
mechanical manufacturing tolerances. The ultrasonic measurement of the pre-load gives the
information about the tension inside of the bolt, independently of mechanical uncertainties. This
consists in an in-situ measurement. More, in some cases, the ultrasonic method allows knowledge
of the preload on bolts already tightened, without untightening. This method is called bi-wave
method, and has many connections with birefringent method.
Examples of application of the method are presented about the differential mode case, which is
largely known and industrialized, and in the case of bi-wave method, which lead to several on site
applications, performed by CETIM with a prototype equipment. |
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