Modelling issue with Abaqus for simple lifting slings hanger

[BritMechEng]

Hello all, this is my first professional post so really don't know how it works and recently graduated in mechanical engineering.
Along my new professional career, I'm working in FEA and I've been training by modelling some simple stuff and more complex ones.

This one is a bit tricky since I've tried to create a simple model of a hanger for lifting slings (you can see its picture below).

As you can see, it seems like there's a shaft of roughly 100 mm long and an arc supposed to be 25mm radius. This is the hypothesis I went with.

However, when I do the numerical analysis I get a global stiffness matrix which determinant is equal to 0. Here's the numerical analysis below.

To find the global stiffness matrix, I used the formula below.

So when I modelled everything on abaqus, I got some decent results. However, my numerical analysis doesn't work.
I thought about using a beam element.
Would you have any ideas ?
thanks a lot for your time.

 

[FEA way]

Matrix with zero determinant is called singular matrix. In case of stiffness matrices this happens when the model is underconstrained. Your node 1 should be fixed in all degrees of freedom. Also use beam element instead of truss one since this will work in bending.

 

[karachun]

I`ll put my two cents. This hook is welded to C-channel beam? If so then beam don’t look too rigid, it will twist at some angle under load and your computational results may not match real life behavior. You can add some portion of beam, up to point where beam constrained to the wall.

 

[IRstuff]

Next time, you should post ABAQUS-specific questions in the ABAQUS forum.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[rb1957]

I think your problem is that you using a truss element to describe a curved beam.

break the problem into pieces …

1) consider the beam in isolation … as a curved beam with full constraint at the end.

2) then consider the hanger in isolation … add the straight section, cantilevered off the supporting beam.

3) include the support beam … model a section of the supporting beam, so that the base of the hanger (fixed as it may be to the supporting beam) can deflect based on the stiffness of the supporting beam.

another day in paradise, or is paradise one day closer ?

 

[BritMechEng]

Thank you all for your answers and time.

In my numerical model, node 1 is fully constrained. I think I forgot to write down some 0 in the location of my node 1.

I agree with the beams however my theoretical knowledge on beams is limited. Im Just aware of the beam element type from FEA.


PS: if I may, would anyone know some good introduction to vibration models in both numerical and software analysis?

Cheers from Britain

 

[FEA way]

The general algorithm used in hand calculations with beam elements is the same as with truss elements. Only matrices are different.

When it comes to resources about structural dynamics with FEA I recommend the book "Finite Element Procedures" by Bathe. But if you want to start from more practical aspects then try "A Finite Element Dynamic Primer" from NAFEMS.