What are the stresses in a lifting shackle and how do I calculate them?

[willwoll100]

Hello All,

I'm currently designing a lifting shackle to aid the recovery of a ROV, my problem is that I'd like to do some hand calculations to find the stresses in the shackle but I'm really not sure as to where to start.

I know how to calculate the stresses in the fixing holes but it's the point where either a hook or another shackle will be used.

I've looked all over the net and in Roark's but to no evail.

Please see the attached image.

Regards

Will

 

[Studiot]

The quick attached sketch shows the situations, I think you are describing.

It shows the lifting hook or bar applying double shear to the inverted U of your shackle. The lifting bar will also be in double shear, shown by sections AA and BB.

You should not be designing lifting apparatus if you do not understand this.

If you use a hook an additional consideration will be opening of the hook due to bending.

 

[willwoll100]

Thanks for the reply, I do understand what effects will be apparent on the 'shackle' due to the loadings.

I don't think that a true double shear will be applied, my thinking was that there will be a moment applied due to the inverted U wanting to become a V and also a Hertz contact stress.

I think I need to know the best way to calculate the bending moment so that I can put it into a curved beam equation.

 

[Studiot]

Conventional design usually follows Arthur Morley.

In his book " Strength of Materials" he gives extensive theory for hooks, rings, chain links etc.

The actual stength depends upon the cross section shape.

Wilson and Quereau at the University of Illinois did extensive testing and published tables to enable design.

"Engineering Exeriment Station Circular16".

There is a short version of the tables in

Strentgh of Materials by F L Singer - a more modern book than Morley.

Google gives this up to date reference.

http://www.crcnetbase.com/doi/abs/10.1201/9781420017823.ch14

 

[willwoll100]

Thanks a lot Studiot

 

[Studiot]

Two more things,

Lifting gear is (should be) made of pretty chunky pieces of ductile metalwork.
As such there should no contact stress, brittle or fatigue failure issues and the gear should be to stocky to deflect into a V in the manner you suggest.

If you have trouble with the references, I will post the formulae.

 

[Studiot]

There will be contact stresses however you hook it up.

But lifting tackle needs to be so beefy that this is not usually an problem. Also remember the material should be such as not to support failures spreading from the stress concentrations caused by contact stresses.

I once did a failure investigation on rollers supporting about 2500 tonnes that failed in this way because the material was not ductile enough.