# Regarding Force and Moment in Ansys Static Structural.

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• Last Post 19 March 2020
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Chinmay posted this 18 March 2020

Hi,

Let me start with what my problem is. I need to put cover over the stack as shown in below image. It's a plastic part.

Based on my limited knowledge of Ansys, I think this can be done in two ways either by "Moment at center or a force which is always perpendicular to face" as below.

But unfortunately, I am not able to provide force which will always be perpendicular to that face or moment which will give the required result. I tried moment but it's just stretching the part after particular angle of deflection. Force using co-ordinates doesn't work either.

I will be much obliged if you could help me with the same. There might be other ideas that may get the required results and I'll try it out on the part.

- CK

sk_cheah posted this 18 March 2020

Perhaps try a moment about your origin (specified by coordinates) and remote surface at where F is pointing at.

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Chinmay posted this 18 March 2020

Hi,

I did try moment at origin as shown in image above. It just keeps on stretching the part. I don't know about remote surface, I'm kinda new to ansys. Can you please elaborate so I can try it out on my part ?

P.S. I will attach pictures of my results when I applied Moment as soon as I reach home.

- CK

Chinmay posted this 18 March 2020

HI,

I used a moment there and following is the result I obtained.

As you can notice, the highlighted part goes on extending if value of the moment is increased.

peteroznewman posted this 18 March 2020

I recommend you slice the solid into three parts. Only the center part needs to be Flexible.

The lid and base don't need to be included in the bending of the plastic hinge.

This much smaller solid body should be meshed with much smaller elements.

You need at least 4 elements through the thickness. If you slice the uniform cross-section of the hinge, you can use Method = Sweep and put 8 elements through the thickness while using Hex elements.

Add Plasticity to the material model. For example, Bilinear Kinematic Hardening where you enter the Yield Strength and Tangent Modulus. A simple way to model plasticity is "perfectly plastic" which means the Tangent Modulus = 0.

Chinmay posted this 19 March 2020

Hi, Thank you for the reply. I will start with making the solid part into 3 different parts, make only hinge part as flexible and others as rigid. I will use fine hex mesh on hinge with at least 8 elements through its thickness. I will search on how to model plasticity for that hinge but I didn't understand where and how to provide moment to get the desire output.

P.S I need to focus on all the three parts simultaneously, it's not just analysis on hinge. It's just the first part of my problem.I need to proceed with fatigue analysis on hinge as well as locking arrangement of the part, I need animation as result too. I will post whatever results I get. Thank you Sir.

Edit: My material is PA66 with density 1140 kg/m^3 but I am unable to find tangent modulus for it.

- CK

peteroznewman posted this 19 March 2020

It might be simpler to assign a remote displacement to the cut face on the lid side. Then you can create a 180 degree rotation of the cut face as the displacement. Make sure to turn on Large Deflection On under Analysis Settings.

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Chinmay posted this 19 March 2020

Hi,

- CK

peteroznewman posted this 19 March 2020

Attached is an ANSYS 19.2 archive that rotates the hinge 170 degrees.
You can animate this result.

I assume the next step you want to do is to have the snaps close. To do that you will have to change the rigid body to a flexible body and add frictional contact between the snap faces. This will greatly increase the number of nodes and greatly increase the solve time. Good luck!

Attached Files

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Chinmay posted this 19 March 2020

Omg ! You are a genius. I was stuck on this problem for three days. I am currently trying to figure out how you did it. Yes, you are right about next part of the problem. Because I couldn't figure this rotation part, I gave linear displacement to top cover to snap fit it into the stack using friction contact. After figuring out your method, I will try snap fit along with it. After that I need to figure out how to produce fatigue for 100 cycles so the hinge as well as snap fit lock doesn't break. Again thank you very much Sir.

- CK