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Ti bolt strength in sheer - one for mech eng
02GF74 - 23/4/20 at 07:48 AM

I have a M6 Ti bolt in a threaded Aluminium alloy tube which goes through two pieces so is acting in sheer and would like my calculations for maximum load in sheer to be checked.

P1 and P2 are the two pieces side by side with a hole drilled and tube/bolt going through them.

-----------
| P1 | P2 |
| | |
-----------
tube with bolt
-----------
| | |
| | |
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I am ignoring any clamping force as that I know increases the load due to it being transferred to the two pieces clamped. also ignoring the metal used for the threads.


Ti M6 bolt; sheer strength 50,000 psi
diameter 5mm (ignoring thread)
area = 16.64 mm2
16.64 / 645.16 x 50000 = 1,289 lb = 586 kg

Al 6063 8mm tube (ignore thread); sheer strength 22000 psi
50.27 0 - 28.27 = 22.00 mm2
22 / 645.16 x 22000 = 750 lb = 341 kg

total for both = 927 kg ?!?!

Note: / 645.16 convert from mm2 to in2

So basically I can hang my kit car, myself and a fair amount of luggage from a 6 mm bolt?????

Alternatively I can fit the bolt (ignoring the tube) in two pieces of steel and put it in a vice. I can measure the torque applied to the vice handle by using a tube of known length and scales.

I can measure jaw travel corresponding to turns on the handle i.e. gearing; but how would that convert to linear force?

AdamR20 - 23/4/20 at 10:16 AM

Sounds about right to me.

I know BAE drag fighter planes around using 4x M5 bolts in shear, with a massive safety margin built in.

AlexXtreme - 23/4/20 at 12:53 PM

I dont think you can add the values as they have different stiffnesses and shear elongations... metals are not my strong point (I am a composite structural engineer!).

BTW to covert psi to N/mm2 / 145

02GF74 - 24/4/20 at 07:32 AM

quote:
Originally posted by AlexXtreme
I dont think you can add the values as they have different stiffnesses and shear elongations... metals are not my strong point (I am a composite structural engineer!).


me neither, I can accept that so ignoring the contribution of the Al tube, which I don't think will make the structure weaker, it is at least 586 kg, which is over 5x my weight - seems massively strong.

coyoteboy - 24/4/20 at 11:18 PM

People are often shocked what tiny fasteners can hold. That's why people rip the female threads out of aluminium parts regularly You're going to want to have a factor of safety or two in there - thread forms cause stress concentrations and combined loads from other directions won't help, but a plain old M5 is a tough cookie when loaded correctly. Take a look at the clamping loads you can impart with the max allowable torque on an M5 - you'd be shocked again.