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Yes! I have a layout for a 6 bolt test fixture to be used in our Instron and will be ordering the hardware shortly. There have been some programmatic challenges that put this problem in the background but we are still moving forward!

desertfox Yes I will post updates as we test and implement the solution, I am very grateful for everyone’s time and consideration. That is an interesting idea I have never seen a product like that. At a quick glance it appears that they do not have any M6 A4-80 options, I am still tied to...

desertfox Thank you, I have presented the concept and it has been well received. I plan to make a test fixture for our Instron with a scaled down bolt pattern of 4 or 8 bolts and test the separation force. I think it will be a nice way to prove out the torque method and wrap up the solution...

Hydtools Please see the section on bolt stiffness here : https://mechanicalc.com/reference/bolted-joint-analysis The thread length I am referring to above is the length of the thread within the grip. The bolt is 35mm long, 11mm shank and 24mm thread, but only 13mm of threaded length is in the...

I wrote the Kb formula wrong, I corrected it. There are two areas we need, one for the shank and one for the threaded section, the new bolts will be partially threaded. The threaded section area is 20.1mm^2 and the shank area is 28.3 mm^2. The length of the threaded section in the grip is 13mm...

IFRs No I do not have a pattern other than hitting them twice in a star pattern, where can I find information on establishing a pattern? desertfox The grip length is 24mm Here is how I got Kb Eb = 194.6 GPa 316 stainless at 293K length of shank = 11mm length of thread in grip = 13mm K =...

desertfox I see your point about the error, I will knock the initial preload to around a 1 kN if possible, thank you.

desertfox T = (.2)*(.006)*(2400) = 2.88 Nm 2400/9600 = 25% of the preload kb = 1.88e08 N/m bolt stiffness kj = 5.03e8 N/m combined stiffness of the washer and aluminum pitch = 1mm For greased threads I have seen .2 as a K factor but please advise otherwise. 2.88 Nm (~25 in-lbs) is near...

I feel like I am ready to submit the design: -56 X M6x1mm 35mm length DIN 912 A$-80 socket head cap screws. -Preload to 9.6 kN by first torqueing to 2.88 Nm (~2400 kN preload) in a star pattern then repeat turning 19 degrees. -minimum factor of safety on joint separation at 4K = 1.96 I think...

desertfox The preload goes from 9.7 kN initially to 8.73 kN after relaxation, then from room temp to 3K it drops to 5.9 kN from the differential thermal contraction. The script I wrote with the NIST data makes switching between materials very simple so all of the correct material properties are...

desertfox Shoot- the invar 36 I will use for the washers has a yield strength of 276 MPa so I am limited to 11 kN before the bolt will embed in the washer. 3DDave I looked into this method and I think this will be our best approach, does ±15% error sound reasonable? I realized that Inconel...

desertfox The proposed washer in this example has an OD of 12mm, and ID of 7mm and is 3mm thick.

desertfox At 3K there is still 6.35 kN of preload left, that is possible because of the invar washer. The washer is reducing the total thermal contraction of the joint to more closely match the bolt and therefore looses less preload. If the washer was very thick, over a centimeter, the preload...

If possible I would like to stick with tightening the bolt with an input torque, in its assembled state we wouldn't have space for a hydraulic tensioner or anything like that. The aluminum contracts more so unless you make a very thick washer, the preload goes down with temperature. I am not...

Here is the current state of the design: -56 bolts preloaded to 10.5 kN -3mm thick invar washer, 12mm OD -2 mm counterbore in bobbin before threads I am calculating the joint stiffness in steps from room temperature down to 3 K using the NIST data, the joint constant at room temperature is...

I wrote a script that uses the NIST cryogenic material data (https://trc.nist.gov/cryogenics/materials/materialproperties.htm) to calculate the separation force from room temperature down to 3 K for varying washer thicknesses, preloads, etc. . It works and I am closing in on the final design but...

hydtools I like to use forming taps when tapping small holes in C101 copper especially, without flutes the taps are much stronger and have a tendency to not break off. I have never tried them in aluminum or with anything larger than an M4 but I will look into it.

desertfox The wall thickness is actually 18.4mm, why the bolts are not centered is still a mystery to me. Since I would prefer to reuse the cover if possible, I am somewhat tied to an edge distance of 8.5mm.

desertfox Ivar has extremely low thermal expansion, note the figure from 29.12.20, so I will use invar washers of a specified thickness such that the room temperature preload is not lost. Think of the washer as taking up the ‘slack’ from the contracting aluminum. I will need to calculate the...

hacksaw I totally agree and will make sure we go over everything before implementing any new designs or testing. desertfox Great I am glad we are on the same page. I think I am going to propose the following revisions: -Double the number of bolts to 56/ea -specify Invar washers/spacers...