How to calculate the failure point of a pin

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Discussion Overview

The discussion revolves around calculating the failure point of a pin used in a device suspension system. Participants explore the mechanics of shear strength, material properties, and the potential for failure modes, including deformation and shear failure. The conversation includes both theoretical calculations and practical experimentation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant describes a device where a pin is used to secure a bar within a block, expressing interest in calculating the weight capacity before failure.
  • Another participant suggests that while calculations can be made, manufacturers typically test pins and publish results, emphasizing the importance of material properties and fit.
  • A third participant recommends using Google image searches to visually identify similar problems, potentially aiding in understanding the mechanics involved.
  • A participant clarifies the dimensions of their setup, noting the materials involved (aluminum for the block and bar, stainless steel for the pin) and speculating on the failure modes.
  • Concerns are raised about the pin's failure mode, with one participant suggesting that the softer aluminum may prevent sudden failure by deforming rather than shearing the pin.
  • Another participant discusses the mathematical relationship between stress, force, and area, while expressing uncertainty about unit conversions and practical applications of the equations.
  • One participant proposes that conducting a physical test by loading a pin until failure could provide definitive answers.

Areas of Agreement / Disagreement

Participants express various viewpoints on calculating the failure point of the pin, with no consensus on a single method or conclusion. Some emphasize theoretical calculations, while others advocate for experimental testing.

Contextual Notes

Participants mention several factors that could affect the calculations, including material properties, dimensions, and potential failure modes. There is an acknowledgment of the complexity involved in determining the exact failure point.

pete
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Hi, I have a device I'm suspending from a chain and the chain attaches to the body with a pin. I'm curious how you would calculate how much weight a pin like that could take before failing. There is a block on the body and a bar on the end of the chain that slots into the block and the pin goes through both and out the other side so it would have to shear the pin in two, in three actually so it seems unlikely but I would like to learn how to work it out myself so I know for sure.
I tried googling it but I got so many different answers that I got a bit confused so I thought I'd come and ask here?
 
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They can be modeled and calculated, but mostly, the manufacturer will test his bolt or pin and then publish the result. Here is an example:
https://www.portlandbolt.com/technical/faqs/bolt-shear-strength-considerations/

First, let me better described what I think you have. There is a vertical channel through the block where the bar is inserted. Then the bar is held in place with a pin that crosses horizontally through the block and the bar.

It is best to determine the shear failure load by experimentation. It will be dependent on the size, fit, and materials used for the block and the bar. Also, there are other failure modes besides shear. If the block is made of a softer material, it could deformed and allow the pin to pulled through.
 
I like a Google image search for your terms in question. Your mind is very good at picking out pictures of your problem of interest and the pictures may lead to your answer.

https://www.google.com/search?q=SHE...Bs0KHRstCQIQ_AUIECgB&biw=931&bih=570&dpr=1.38
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Thanks for the response. Yes, that's it more or less. The block is just over 40mm wide with a 30mm diameter hole through it and the bar which is also 30mm diameter slides into the hole then a 6mm pin goes through the block passing through the center of the bar. The block and bar are aluminum and the pin stainless steel. The aluminum could deform and loosen up the connection but the block or bar would have to tear themselves apart to actually fail so I'm sure the pin would go first.

I was thinking the block being slightly softer may even help prevent sudden failure as it will be harder for it to behave like a guillotine on the pin.

The link you provided has some information on how to calculate it. I'll haven't had time to read it properly yet but will later.
 
I'm afraid I've never done much maths so I'm not too good a reading stuff like that. To be clear what it means is that the stress on the bolt is equivalent to the force divided by the area. The area of the pin being the radius squared times Pi. I suppose the only difference is that there is no possibility for the pin to bend so when it fails it shears in half, although not in my case with the aluminum. I'm guessing it will all just get twisted up. But really I want it to be well within its capacity so it does not deform.

Maybe the best thing is to just make one up and load it till it fails, then I'll know for sure.

These equations are very neat and make sense but I never understand what units I would put in there to end up with a useful number. Like how much weight can the pin carry.
 

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