Hello,
I am working on bolted joints loosening, when subjected to transversal dynamic loads. In my case, I would like to maximise the damping in the joint to reduce the natural frequencies of the whole structure. But a high damping means a high relative transverse displacement of the parts in contact, and then a high loosening of bolt clamping force. So I need an upper criterion to limit the damping in the joint. It has to be high enough but not too much.
Thus, I am looking for this criterion. It has to be linked to energy dissipation through the joint and it would relates this energy to the loosening...I cannot find it at the moment, that is why I ask the question.
Thanks a lot.
Rémi
To exclude bolt loosening caused incremental sliding, we may to change the external friction as dissipative factor to internal one. From technological point of view this looks as introducing to frictional joint the relatively complient antivibration pad made of viscoelastic material. Or, we may to minimize magnitude of sliding by reducing it to low-amplitude fretting (microslip). The energy dissipation will be maximal for defined value of friction coefficient (see, please, Fig. 4 in paper "Numerical Study of Microslip in Indenter-Elastic Foundation Contact // Soviet Journal of Friction and Wear. – 1985. – Vol. 6, No. 2. – pp. 73–78). Best regards
Hello,
thanks a lot for your answers it has been very helpful.
Best regards
I work on practical applications of infrared thermography. We noticed that , in airplane aluminum frames containg a big number of rivets, a loosened rivet reveals a higher temperature if the frame is subjected to 22 kHz ultrasonic vibrations. Since the released nergy is related to a grade of bolt 'looseness' and the temperature is linearly proportional to the released energy, the temperature elevation in a bolt connection may characterize its quality. So, load a bolt connection mechanically and measure the temperature rise.
Dear Vladimir, how much temperature and temperature gradient do you observe in your diagnostical tests? Of course, these values are depended on magnitude and frequency of ultrasonic vibrations as well as on thermal conductivity of contacting parts. Best regards, Serge
22 kHz is a typical frequency in such tests. We use a magnetostrictive powerful ultrasonic device with electrical power at the indentor from 200 to 2000 W. What is a real 'ultrasonic' power at a defect site, nobody knows but it is assumed from tens to hundreds of milliwatt. A non-defect sample remains cold, i.e. is is at the ambient temperature, while a loosened rive increases its temperature by 1-10 oC above the ambient.
Thanks everyone for your answers.
Vladimir,
the criterion I would like to develop is based on the idea that the more energy you dissipate, the more you decrease the natural frequency. But as you say, energy dissipation means temperature rise.
So do you think the loosening behaviour of a bolted connection has to be studied as a thermomecanical dynamic problem, as the temperature rise means dilatation and dilatation means more loosening etc ? For the moment, I did not take this into account as it seems very complicated to model.
Rémi
Hi, Remi:
Yes, I believe that in general this is a thermomechanical problem where I'm not strong. My personal field is heat conduction in inhomogeneous media (defect detection by infrared thermography). I'm not sure about dilatation. I think frequency, mass and vibration amplitude are good enough parameters to evaluate released energy. By known energy, it'd be possible to estimate temperature rise.
Ok Vladimir thanks I will try to take the heat conduction into account in my model.
Best regards. Rémi
Dear collegues, of course, thermomechanical problem is not simple, although it may be solved successfully by application of finite element method (and available software). For the beginning the simple scheme for one or two bolts connection may be considered as a test example
I sure that similar calculations are described in literature. The numerical results will follow good to your experimental data. Best regards, Serge
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