Moment load

[feaplastic]

Hello,

I need to apply moment load on my whole body (1200 Nm) about some reference point.

first option, make analytical rigid body and linked with reference point. It leads to contact analysis and makes it difficult. Does not converge.

second option, kinematic coupling. But it removes boundary conditions whcih exists in original part.

Solver is abaqus. Any idea.

Thanks for your replies.

feaplastic

 

[johnhors]

Ideally you should apply the moment as a pressure distribution over a finite area. If the area in question is planar then this can be accomplished very easily using Roshaz on your existing mesh. If it's non-planar, it may still be possible, but it will certainly be more involved.

 

[feaplastic]

Thanks johnhors. Could you please explain further, how to go about it. What is Roshaz? Excuse me for my ignorance.

feaplastic

 

[GBor]

Roshaz is another analysis package, but it can also operate as a pre- and post- processor for Abaqus. I market it in the US and don't want to give a "sales pitch" on Eng-Tips, but if you want more information, visit roshaz.borowskiengineering.com

In short, it has some loading features that make things like this very easy. You basically apply a pressure load to a face, but you can designate that pressure in a variety of ways including telling the software to distribute a load. A simple calculation will tell you what that load needs to be.

Garland E. Borowski, PE
Borowski Engineering & Analytical Services, Inc.
Lower Alabama SolidWorks Users Group
Magnitude The Finite Element Analysis Magazine for the Engineering Community

 

[feaplastic]

Thanks Gbor,

I gone through the website. But, What about the methods which i explained in my original post. Is it possible to achieve what i want to do using those methods.

feaplastic

 

[crisb]

I have applied moments to a point and then connected that to one face using a rigid link. But be careful with the DOF as you need all 6 DOF for this link. However I agree with the above posters that its better to apply the moment as a varying pressure to particular faces.
Is the lack of convergence due to this moment, or because its a contact analysis. One has to be careful to avoid rigid body modes (including torsion) and get the contact faces orientations etc correct.

 

[GBor]

Not being familiar with the geometry of your model makes it difficult to explain, but Roshaz offers several loading scenarios which may work for your situation. As JohnHors stated, if you have a planar surface in your model, Roshaz can map a face to that planar surface and you can apply a force or a distributed load to the planar face. If it isn't planar, it may still be able to apply it through either some orphan mesh loading capabilities or through some simple geometrics.

I haven't worked with Abaqus, but I believe the input and output of Roshaz is fairly seamless. I've used it with Calculix, Nastran (a little), and used it's internal solvers, but the internal solvers are for static analyses.

crisb points out another method. The easy way to handle the DOF issues is simply to make your rigid beams tie from your single point to several nodes on the surface of your model and then either penetrate into interior nodes with the beams or tie them to adjacent surface nodes. You can't use the Nastran formulation of "Rigid" for this because it generally requires a Master node and a Slave node, but a standard beam formulation with a high modulus (E), high inertia (I), etc. should work.

 

[feaplastic]

Thanks again GBor.

I understand abt the ability of Roshaz. Hope, you know the influence of engineers in any organisation. Straight away i cant ask for a new facility. So, I am trying to do with abaqus.

Abt other method, i am little confused with beam connection which you explained. Moreover, is it possible to calculate pressure value equivalent to my moment by hand calculation or by some other means. Approximate would be enough for initial calculation.

Crisb,

Samething i have done. Created a reference point. analytical surface is linked with ref point as rigid body. Constrained ref point in 5 DOF except x axis, abt which i want to apply moment. But, no success so far.

Let me try further and reply. Hope, users can guide me to find equivalent pressure value.

Thanks for your time and replies.

feaplastic

 

[crisb]

feaplastic

Its a while since I did this and remember it was easy to mess up the rigid link by having wrong degrees of freedom and not apply the loads (especially moments and torsion) you think are applying. All software is different and I do not know Abaqus. In my program this method works fine and its not necesary to use a dummy beam or penetrate to internal nodes.
I think I had the loads/moments applied to a point which was the master of a rigid link with the slave as a surface/face on the body. I think you need all 6 degrees of freedom active otherwise the moments dont get transferred down the rigid link. Also if the model is all 3D elements make sure you havent turned off the rotational degrees of freedom.

 

[crisb]

"Moreover, is it possible to calculate pressure value equivalent to my moment by hand calculation or by some other means."

pressure = moment/section modulus

look in any structures book

 

[feaplastic]

Hello Crisb,

Method which u suggested works fine. My rigid surface rotates as wanted and contacts my original model. But, i get very less displacment and stress. To explain, i simplified geometry and did it as follows.

1. Original part - Flat 400*400*50 mm

2. Rigid surface - 100*100 mm - Tie constrained with original model (to avoid contact converg. problem)and positioned at top center of original model.

3. Ref point - 50 mm away from bottom middle point of original model.

4. Moment applied - 1200000 Nmm

Material: youngs modulus 25000 MPa. Poisson Ratio :0.35

Result :

Displacement: in the range of 10^-4 mm
von mises Stress: in the range of 10^-5 MPa

IS my load very less? i expected a lot of stress. Same case with my original model which has some curved, bent surfaces with more or less same dimension.

Where i have done a mistake. How to calculate amount of force on my rigid plate due to moment on ref point. How it is distuibuted.

Thanks for your time.

feaplastic