I'm using Siemens NX 10.0 to perform a finite element analysis on a single-bolted joint. My goal is to get the pre-stressed natural frequencies (with changing bolt pre-load) and, at last, the frequency response functions.
Unfortunately, I haven't been able to even get the natural frequencies with changing bolt pre-load. I'm using a model with random dimensions based on an example I watched on Youtube by Matthew Jackson: https://youtu.be/uL9_W2V8tiU
I'm modeling the bolt with a CBEAM element connected to the edges of the holes with RBE2 rigid links (see picture below). I've also defined a surface-to-surface contact between the two plates.
I've uploaded the NX .prt, .fem and .sim files to this discussion.
When I perform a SOL 103 REAL EIGENVALUES analysis with a first statics subcase, the natural frequencies keep constant even when I use bolt pre-loads as different as 1N, 10N, 100N or 1000N.
Can anyone please help me? Thank you so much!
Well, modal analysis disconsider loads inputs. You may try to use displacements instead induced by your desired load. I´m not sure if it works in NX.
The differential stiffness affect of the bolt preload on this geometry is only going to affect the structure immediately surrounding the hole. It is not going to significantly affect the global stiffness of the structure, so the modal frequencies are only going to change slightly.
If I run your model with and without preload affects included, I do get a small change in frequency:
No Preload Preload 272.4328 272.4325 582.9326 582.7915 888.0516 888.0097 972.6120 972.6116 1616.2330 1616.2320 1687.2600 1687.2600 1853.9370 1853.9280 1923.0700 1923.0430 2058.8290 2058.7660 2065.3780 2065.3630
In the attached model, in the "All Subcase Preload" solution, the preload affects the stiffness of the entire structure, so the change is frequency is much more evident.
I´ve tried to run a structural analysis with bolt pre-load and then run modal analysis with those pre-stress and got a little more sensivity results. I don´t know to run with Nastran, I used Ansys. But for small preload range the results do not change significantly.