I am attempting to replace a 38kg solid pin with a hollow 16kg pin - ambitious, I know, but that’s what we’re here for. The pin is in double shear and has an estimated load of 140T, or 1,373.4kN.

FEA
“FEA Boundary Conditions.JPG” shows the layout of my FEA Analysis in SolidWorks Simulation. I’ve applied two separate loads of 70T of the flat sections of the housing (purple arrows). The central member can be thought of as a central strut and is fixed on the flat underside area (green arrows). A global no-penetration contact set has been applied with a friction coefficient of 0.15. The friction coefficient is the only feature holding the pin in place. The maximum stress shows 756.1 MPa on the ID in the 4.5mm gap.

Manual Calculation
“Hollow Pin with UDL on ends_SkyCiv Beam.pdf” shows my attempt at a manual representation, where I’ve treated the pin as a beam. I’ve used the shear force and bending moments to calculate the average shear stress and bending stress respectively. I am aware the FEA and this manual representation is different in the sense that the mid-way point of the beam can bend freely whereas in the FEA and in real life, the pin will flex only to the extent of the clearance in the housing (0.33mm) before fouling. The shear stress is 124.4 MPa (P/A), and the bending 229.9MPa (See “Bending calc.pdf”.

I can see there are some differences between the two methods, and that the FE method fundamentally uses the spring equation which is different to my manual calcs but I wouldn’t have expected such large differences.

Can anyone explain why the FEA results are so high, or my manual calculation is so low? I don’t know which results to work with, which probably means neither.

I’ve attached the SolidWorks files for reference. Let me know if you require more information and i'll have a response within 24 hours.

 

First mistake in hand calculations is the formula for moment of inertia is wrong. The correct formula is

I = pi (Do^4 x Di^4) / 64

Ref: http://www.engineeringtoolbox.com/area-moment-inertia-d_1328.html

I would also suggest to re-check your bending moment and you should get a close enough answer if FEA is correct.

I see that

Sigma bending = (calculated bending moment x distance from neutral axis) / moment of inertia

distance from neutral axis would be equal to the Ro (outer radius) since the x-section is symmetric around that axis.

Correct me if I am wrong.

 

Hi Muhammad

Thanks for the response.

I'm going to assume you've made a typo, since i couldn't see the equation you gave anywhere in the webpage you referenced.Correct me if i'm wrong or missing something.

Your reference states for hollow circular cross sections:

I = pi(do^4 - di^4) / 64

It also seems my eq. is written with respect to the radius, whereas yours is written with respect to diameter. I believe they are the same equation.

 

Also, yes that is the bending equation I have used. I agree that y = ro

 

Yes you are right, my apologies, i missed the radius/diameter completely.

 

Also, isn't your pin hollow circular x section? That's what i understood.

 

Yes it is hollow, however you have written I = pi (Do^4 x Di^4) / 64
You have multiplied Do^4 and Di^4, rather than finding the difference. Hence why i assumed you made a typo.

 

Yes Shane. You are right again. Sorry buddy I was trying to look at your problem and do something else.

Did you manage to resolve your FEA? Mesh alteration, different boundary condition or something else? I am interested to know.

 

I've still got a large discrepancy between manual calcs and FEA. I will let you know if i find out whats going on. Thanks for your interest