Shear stress in hollow pin 2

[remiw]

Hi,
I have a 4" diameter pin that is used for the pivot of a 50 ton box on a truck. To make installing the pin easier as well as saving material cost I want to us a hollow pin. How would I go about determining the max shear stress that the pin will need as well as the mas inner radius that I could use?

Thanks,

RBW

 

[rb1957]

i don't know how much cost you're going to save, either you or someone else is going to be machining out the core, and that'll cost (i'd have thought that a hollow pin would cost more). it will save some weight though.

shear stress depends on material, commonly somewhere between 50 and 80 ksi for steels.

inner radius depends on the geometry of the lugs, ie the peak bending moment in the pin ... so we'll need more details before we can help in any meaningful way.

 

[Cockroach]

Use AISI 4140 HRc 28-32 material and drill your 4.0 OD pin to 3 5/8 ID. Your minimum allowable wall thickness is 0.173 inches, thus meeting your load requirements.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[vonlueke]

remiw: What are the following dimensions and data? Thickness of inner lug (t1), thickness of clevis plate (t2), distance between your two clevis plates (a1), hole diameter in inner lug and clevis plates (d0), alloy and material specification of pin material, alloy/material spec. of clevis plates, alloy/material spec. of inner lug (if different from clevis plates).

Or if this is a single-shear connection, what is the thickness of, or pin engagement depth in, each of the two plates (t1 and t2), hole diameter in each of the two plates (d0), alloy/material spec. of the pin and each plate?

 

[dmech]

remiw,
As others have pointed out, there is a need for more information. The three most important being:

1) How many sheer locations are present (i.e. single sheer, double sheer, triple sheer, etc)?
2) What is the standard factor of safety used for the piece of equipment this pin will operate within (this is really an indicator on how well the material properties, environmental conditions, and operating loads are understood)?
3) Is there cyclic loading of the pin (if yes then a fatigue strength must be used, otherwise a basic static analysis is sufficient).

As for my quick back of the envelope answer to you question without consideration for the above important points:

tau1 = F/A = (50 tons * 2000 lbs/ton)/(pi*(4^2-3.5^2)/4)

Where, F is the force being supported by the pin, and A is the cross sectional area of the pin. I've used a 4130 4" OD tube with a 1/4" wall (3.5" ID). This is a stock tube from Tube Service Co. (Tensile yield strength of 70 kpsi)

tau1 = 33.9 kpsi (single sheer and factor of safety NOT applied)

tau2 = tau1/2 = 17.0 kpsi (double sheer and factor of safety NOT applied)

IMPORTANT: It looks as though your design may be feasible. However, a more complete understanding of the problem and an appropriately applied factor of safety are required to ensure the pin won't fail and KILL SOMEONE!!!

 

[rb1957]

remiw,

several posters have replied to your question about shear stress, and these responses look reasonably sensible.

i wonder about the bending stress in your pin ?

 

[ornerynorsk]

Just use solid. I assume that this is a mining/earthmoving application. Don't screw around with a tube, you'll be sorry later. Cockroach - a .173 wall ??????? You're joking! You've never seen the treatment that offroad equipment is subjected to.

 

[Zapster]

My seat-of-the-pants evaluation would be:
The drilled pin (0.25” wall) would be subject to cyclic loading. If the pin did not fail from buckling, it would probable fail from cyclic deformation.

 

[Zapster]

Oops, I forgot to add, how easy will this pin be to remove/reinstall if there is any deformation?

 

[rb1957]

i guess there are two answers to that ... either
deformation = difficult to remove, or
to paraphrase Aristole, "with a big enough sledge, i can move any pin"

 

[Cockroach]

OrneryNorsk....no I'm not joking. Given the input information, 0.173 inch wall as per material stated and FOS. This is a single shear value.

Off road? This is an assumption beyond the original statements of Remix, as is cyclic loading.

Remember, this forum is designed to brainstorm, not provide answers for projects underway from an employer!

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada