Okay then.
So basically the problem is this.
I have a honeycomb core and want to analyze its shear properties.
Experiments have been done according to the ASTM-C273 standards, which gave
us some results about the core. The ones that are of interest to me are the
buckling initiation of the walls, the elastic yield point, and the overall
shape of the buckled walls. We have the results from the experiments and
wanted to move on to creating a FEM/FEA of the same core and see if the
model will be in accordance with the experiments.

So I have created a model of the exact core ( Number of cells, material
properties) without the loading plates( to save computational cost), the
plates have been replaced by boundary conditions where the bottom is fixed
on UX,UY, UZ, and the top nodes create a rigid region (cerig Command) with
a master node to apply a displacement (as of the experiment which is
displacement controlled), MasterNode is fixed in all rotations (ROTZ, ROTY,
ROTZ). So far so good, the problem lies when running the model. Currently,
I wasn't able to make the analysis results match the experimental ones (
Force vs Displacement curves) because the FEM is much stiffer, almost  3
times, than the actual core.

Another error I get when running the analysis is- excessive element
distortion-, this error prevents the analysis from running until the end,
my load is 0.5 mm and it stops at 0.06.

[image: image.png]

Στις Δευ 20 Φεβ 2023 στις 6:43 μ.μ., ο/η Caba, Aaron C (US) <
aaron.caba@baesystems.com> έγραψε:

On 21/02/2023 07:38, AntonisΤ wrote:

Please could you give more detail about the boundary condition at the
bottom of the model; are all DOF fixed or just the minimum number
required to represent the boundary?

--
Martin Liddle
Chesterfield, Derbyshire, UK.

The bottom of the core is restricted in UY, UX, UZ just that nothing else.

Στις Τρί 21 Φεβ 2023 στις 11:46 π.μ., ο/η Martin Liddle <
xansys05@tynecomp.co.uk> έγραψε:

On Tuesday, February 21, 2023, AntonisΤ useratsi98@gmail.com wrote:

This is because you’re replacing the supporting plate by fixed boundary
conditions. This dramatically increases the stiffness in your model. Maybe
you should start thinking about modeling the plate instead of the fixed
displacements. Even if it becomes computationally intensive.

The plate in the actual test can be deformed and it behaves elastically.
However, the fixed supports neglects the elasticity of the plate and hence
your stiffer FEA Model.

Well, that is an old debate. In such cases, try to apply your load more
gradually (increase number of sub-steps or reduce time step). Also, you
might want to improve your mesh quality. Look up the web for the commands
that controls the nonlinear solutions.

Good Luck!
MAG

--

---====
Mohammad A Gharaibeh, Ph.D.
Associate Professor
Department of Mechanical Engineering
The Hashemite University
P.O. Box 330127
Zarqa, 13133, Jordan
Tel: +962 - 5 - 390 3333 Ext. 4771
Fax: +962 - 5 - 382 6348

---====

It may be a good idea to start with a coarser mesh while you debug your model.  You can learn and experiment a lot more with iterations of 1 minute vs. 60 minutes.

Are you running in large displacement (NLGEOM,ON)? Is your expected load-deflection curve linear or do you expect any non-linear geometric behavior?

Are you sure you are applying your load in the same direction (angle) as your experiment?  The measured stiffness will be a function of the load direction.  This might be another reason to model more of the fixture.  You can make the fixture mesh coarse if you use bonded contact between the face sheet and the fixture without adding much to the runtime.

The excessive element distortion may be due to local buckling in the core.  Maybe run a buckling analysis to see what load the honeycomb starts to buckle.

Like someone else said, increase the number of sub-steps (like 1,000 or 10,000) to see if ANSYS can get ‘through’ the difficult spot.

Aaron C. Caba, Ph.D.
Sr. Principal R&D Engineer
BAE Systems, Inc.
4050 Peppers Ferry Road, Radford VA 24143-0100
www.baesystems.comhttp://www.baesystems.com/

From: AntonisΤ useratsi98@gmail.com
Sent: Tuesday, February 21, 2023 2:39 AM
To: Caba, Aaron C (US) aaron.caba@baesystems.com; XANSYS Mailing List Home xansys-temp@list.xansys.org; xansys-temp-request@list.xansys.org
Subject: Re: [Xansys] Re: [External Email] FEA/FEM expert

External Email Alert

This email has been sent from an account outside of the BAE Systems network.
Please treat the email with caution, especially if you are requested to click on a link, decrypt/open an attachment, or enable macros.  For further information on how to spot phishing, access “Cybersecurity OneSpace Page” and report phishing by clicking the button “Report Phishing” on the Outlook toolbar.

Okay then.
So basically the problem is this.
I have a honeycomb core and want to analyze its shear properties. Experiments have been done according to the ASTM-C273 standards, which gave us some results about the core. The ones that are of interest to me are the buckling initiation of the walls, the elastic yield point, and the overall shape of the buckled walls. We have the results from the experiments and wanted to move on to creating a FEM/FEA of the same core and see if the model will be in accordance with the experiments.

So I have created a model of the exact core ( Number of cells, material properties) without the loading plates( to save computational cost), the plates have been replaced by boundary conditions where the bottom is fixed on UX,UY, UZ, and the top nodes create a rigid region (cerig Command) with a master node to apply a displacement (as of the experiment which is displacement controlled), MasterNode is fixed in all rotations (ROTZ, ROTY, ROTZ). So far so good, the problem lies when running the model. Currently, I wasn't able to make the analysis results match the experimental ones ( Force vs Displacement curves) because the FEM is much stiffer, almost  3 times, than the actual core.

Another error I get when running the analysis is- excessive element distortion-, this error prevents the analysis from running until the end, my load is 0.5 mm and it stops at 0.06.
[image.png]

Στις Δευ 20 Φεβ 2023 στις 6:43 μ.μ., ο/η Caba, Aaron C (US) <aaron.caba@baesystems.commailto:aaron.caba@baesystems.com> έγραψε:
Antonis,

You just replied to me, not to the list.

• Aaron

From: AntonisΤ <useratsi98@gmail.commailto:useratsi98@gmail.com>
Sent: Monday, February 20, 2023 11:02 AM
To: Caba, Aaron C (US) <aaron.caba@baesystems.commailto:aaron.caba@baesystems.com>
Subject: Re: [Xansys] Re: [External Email] FEA/FEM expert

External Email Alert

This email has been sent from an account outside of the BAE Systems network.
Please treat the email with caution, especially if you are requested to click on a link, decrypt/open an attachment, or enable macros.  For further information on how to spot phishing, access “Cybersecurity OneSpace Page” and report phishing by clicking the button “Report Phishing” on the Outlook toolbar.

Isn't it already posted on the list?

How cad do I post it?

Στις Δευ 20 Φεβ 2023 στις 6:01 μ.μ., ο/η AntonisΤ <useratsi98@gmail.commailto:useratsi98@gmail.com> έγραψε:
Will do. Can you provide any help?

Στις Δευ 20 Φεβ 2023 στις 3:42 μ.μ., ο/η Caba, Aaron C (US) <aaron.caba@baesystems.commailto:aaron.caba@baesystems.com> έγραψε:
Antonis,

That is much informative.  Please post it to the list so everyone can see and heip.

Aaron C. Caba, Ph.D.
Sr. Principal R&D Engineer II
BAE Systems, Inc. | Ordnance Systems, Inc.

E-mail: aaron.caba@baesystems.commailto:aaron.caba@baesystems.com | Mail:  4050 Peppers Ferry Road, Radford VA 24143-0100
www.baesystems.comhttp://www.baesystems.com/

From: AntonisΤ <useratsi98@gmail.commailto:useratsi98@gmail.com>
Sent: Saturday, February 18, 2023 5:53 AM
To: Caba, Aaron C (US) <aaron.caba@baesystems.commailto:aaron.caba@baesystems.com>
Subject: Re: [Xansys] Re: [External Email] FEA/FEM expert

External Email Alert

This email has been sent from an account outside of the BAE Systems network.
Please treat the email with caution, especially if you are requested to click on a link, decrypt/open an attachment, or enable macros.  For further information on how to spot phishing, access “Cybersecurity OneSpace Page” and report phishing by clicking the button “Report Phishing” on the Outlook toolbar.

Okay then.
So basically the problem is this.
I have a honeycomb core and want to analyze its shear properties. Experiments have been done according to the ASTM-C273 standards, which gave us some results about the core. The ones that are of interest to me are the buckling initiation of the walls, the elastic yield point, and the overall shape of the buckled walls. We have the results from the experiments and wanted to move on to creating a FEM/FEA of the same core and see if the model will be in accordance with the experiments.

So I have created a model of the exact core ( Number of cells, material properties) without the loading plates( to save computational cost), the plates have been replaced by boundary conditions where the bottom is fixed on UX,UY, UZ, and the top nodes create a rigid region (cerig Command) with a master node to apply a displacement (as of the experiment which is displacement controlled), MasterNode is fixed in all rotations (ROTZ, ROTY, ROTZ). So far so good, the problem lies when running the model. Currently, I wasn't able to make the analysis results match the experimental ones ( Force vs Displacement curves) because the FEM is much stiffer, almost  3 times, than the actual core.

Another error I get when running the analysis is- excessive element distortion-, this error prevents the analysis from running until the end, my load is 0.5 mm and it stops at 0.06.
[image.png]

Στις Παρ 17 Φεβ 2023 στις 4:01 μ.μ., ο/η Caba, Aaron C (US) <aaron.caba@baesystems.commailto:aaron.caba@baesystems.com> έγραψε:
Antonis,

You haven't provided us anything anyone can act on with your last two posts.  We know you have a problem, but not what it is.  You've given a very general overview of your simulation, so the only thing we could do is give you very general pieces of advice.  No one is going to take the time to guess what your problems are, or play 20 questions. Mohammad tried, but you failed to answer most of the questions he asked.  The impetus is on you to present:  What your problem is; What research you've done to investigate it (google is your friend); What you have tried that has failed AND what has worked; What results you want from this exchange.

I've always found http://www.catb.org/~esr/faqs/smart-questions.html to be a good place to learn how to ask questions on a forum.  It is long, but well worth the read.

Aaron C. Caba, Ph.D.
Sr. Principal R&D Engineer
BAE Systems, Inc.
4050 Peppers Ferry Road, Radford VA 24143-0100
www.baesystems.comhttp://www.baesystems.com

External Email Alert

This email has been sent from an account outside of the BAE Systems network.

Please treat the email with caution, especially if you are requested to click on a link, decrypt/open an attachment, or enable macros.  For further information on how to spot phishing, access “Cybersecurity OneSpace Page” and report phishing by clicking the button “Report Phishing” on the Outlook toolbar.

The model is a Honeycomb core that's been tested in shear according to the
ASTM-C273 standards. Test coupons are composed of three parts, the core, the adhesive, and the loading plates. In my model, I removed the plates and used boundary conditions to reduce computational time.
Boundary conditions are: bottom of the core restricted at UX, UY, UZ and at the top I have created a rigid region with a master node to apply the load.
Master node is constrained at ROTX, ROTY, ROTZ.
element type used: Shell181
Loading is displacement control. A displacement is applied at the master node and equally distributed on all nodes of the rigid node.
APDL is the program.

Thanks!

Στις Πέμ 16 Φεβ 2023 στις 1:07 μ.μ., ο/η Mohammad Gharaibeh via Xansys < xansys-temp@list.xansys.orgmailto:xansys-temp@list.xansys.org> έγραψε:

Xansys mailing list -- xansys-temp@list.xansys.orgmailto:xansys-temp@list.xansys.org To unsubscribe send an email to xansys-temp-leave@list.xansys.orgmailto:xansys-temp-leave@list.xansys.org If you are receiving too many emails from XANSYS please consider changing account settings to Digest mode which will send a single email per day.

Please send administrative requests such as deletion from XANSYS to xansys-mod@tynecomp.co.ukmailto:xansys-mod@tynecomp.co.uk and not to the list

To add the existing replies, a stiff response likely indicates boundary conditions may be incorrect.  From the images, I see that you have constrained nodes at the bottom and used a RBE-2 style constraint at the top with a pilot node. Is this representative of your experimental setup? You may have to avoid using bc's and instead use frictional contact to mimic the experimental setup especially if the sample is not glued to the plates compressing the structure.

Also are these closed or open walled cell structures? You will have to be careful of the former as they require special treatment to account for air that is trapped as they can resist compressive forces at high pressures.

Note that once the cell wall buckles, you will see a softening response in the global load-displacement curve that will require numerical damping when using the static solver.

-----Original Message-----
From: Caba, Aaron C (US) via Xansys xansys-temp@list.xansys.org
Sent: Tuesday, February 21, 2023 3:06 PM
To: XANSYS Mailing List Home xansys-temp@list.xansys.org; xansys-temp-request@list.xansys.org
Cc: Caba, Aaron C (US) aaron.caba@baesystems.com
Subject: [Xansys] Re: [External Email] FEA/FEM expert

[This sender might be impersonating a domain that's associated with your organization. Learn why this could be a risk at https://aka.ms/LearnAboutSenderIdentification ]

[External Sender]

It may be a good idea to start with a coarser mesh while you debug your model.  You can learn and experiment a lot more with iterations of 1 minute vs. 60 minutes.

Are you running in large displacement (NLGEOM,ON)? Is your expected load-deflection curve linear or do you expect any non-linear geometric behavior?

Are you sure you are applying your load in the same direction (angle) as your experiment?  The measured stiffness will be a function of the load direction.  This might be another reason to model more of the fixture.  You can make the fixture mesh coarse if you use bonded contact between the face sheet and the fixture without adding much to the runtime.

The excessive element distortion may be due to local buckling in the core.  Maybe run a buckling analysis to see what load the honeycomb starts to buckle.

Like someone else said, increase the number of sub-steps (like 1,000 or 10,000) to see if ANSYS can get 'through' the difficult spot.

Aaron C. Caba, Ph.D.
Sr. Principal R&D Engineer
BAE Systems, Inc.
4050 Peppers Ferry Road, Radford VA 24143-0100 https://nam10.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.baesystems.com%2F&data=05%7C01%7Charish.radhakrishnan%40ansys.com%7C3858a904b18e44fe460908db146caf89%7C34c6ce6715b84eff80e952da8be89706%7C0%7C0%7C638126229306252894%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=92R2r5zWKjkbWTYAlnKteZEVYtVLLYzziQ57XOHKE5c%3D&reserved=0https://nam10.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.baesystems.com%2F&data=05%7C01%7Charish.radhakrishnan%40ansys.com%7C3858a904b18e44fe460908db146caf89%7C34c6ce6715b84eff80e952da8be89706%7C0%7C0%7C638126229306409132%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=l1JZvfrouKtiEQHHfdg4Q0GvNKcKmzkEO%2FRNGpsisQQ%3D&reserved=0

From: AntonisΤ useratsi98@gmail.com
Sent: Tuesday, February 21, 2023 2:39 AM
To: Caba, Aaron C (US) aaron.caba@baesystems.com; XANSYS Mailing List Home xansys-temp@list.xansys.org; xansys-temp-request@list.xansys.org
Subject: Re: [Xansys] Re: [External Email] FEA/FEM expert

External Email Alert

This email has been sent from an account outside of the BAE Systems network.
Please treat the email with caution, especially if you are requested to click on a link, decrypt/open an attachment, or enable macros.  For further information on how to spot phishing, access "Cybersecurity OneSpace Page" and report phishing by clicking the button "Report Phishing" on the Outlook toolbar.

Okay then.
So basically the problem is this.
I have a honeycomb core and want to analyze its shear properties. Experiments have been done according to the ASTM-C273 standards, which gave us some results about the core. The ones that are of interest to me are the buckling initiation of the walls, the elastic yield point, and the overall shape of the buckled walls. We have the results from the experiments and wanted to move on to creating a FEM/FEA of the same core and see if the model will be in accordance with the experiments.

So I have created a model of the exact core ( Number of cells, material properties) without the loading plates( to save computational cost), the plates have been replaced by boundary conditions where the bottom is fixed on UX,UY, UZ, and the top nodes create a rigid region (cerig Command) with a master node to apply a displacement (as of the experiment which is displacement controlled), MasterNode is fixed in all rotations (ROTZ, ROTY, ROTZ). So far so good, the problem lies when running the model. Currently, I wasn't able to make the analysis results match the experimental ones ( Force vs Displacement curves) because the FEM is much stiffer, almost  3 times, than the actual core.

Another error I get when running the analysis is- excessive element distortion-, this error prevents the analysis from running until the end, my load is 0.5 mm and it stops at 0.06.
[image.png]

Στις Δευ 20 Φεβ 2023 στις 6:43 μ.μ., ο/η Caba, Aaron C (US) <aaron.caba@baesystems.commailto:aaron.caba@baesystems.com> έγραψε:
Antonis,

You just replied to me, not to the list.

• Aaron

From: AntonisΤ <useratsi98@gmail.commailto:useratsi98@gmail.com>
Sent: Monday, February 20, 2023 11:02 AM
To: Caba, Aaron C (US) <aaron.caba@baesystems.commailto:aaron.caba@baesystems.com>
Subject: Re: [Xansys] Re: [External Email] FEA/FEM expert

External Email Alert

This email has been sent from an account outside of the BAE Systems network.
Please treat the email with caution, especially if you are requested to click on a link, decrypt/open an attachment, or enable macros.  For further information on how to spot phishing, access "Cybersecurity OneSpace Page" and report phishing by clicking the button "Report Phishing" on the Outlook toolbar.

Isn't it already posted on the list?

How cad do I post it?

Στις Δευ 20 Φεβ 2023 στις 6:01 μ.μ., ο/η AntonisΤ <useratsi98@gmail.commailto:useratsi98@gmail.com> έγραψε:
Will do. Can you provide any help?

Στις Δευ 20 Φεβ 2023 στις 3:42 μ.μ., ο/η Caba, Aaron C (US) <aaron.caba@baesystems.commailto:aaron.caba@baesystems.com> έγραψε:
Antonis,

That is much informative.  Please post it to the list so everyone can see and heip.

Aaron C. Caba, Ph.D.
Sr. Principal R&D Engineer II
BAE Systems, Inc. | Ordnance Systems, Inc.

E-mail: aaron.caba@baesystems.commailto:aaron.caba@baesystems.com | Mail:  4050 Peppers Ferry Road, Radford VA 24143-0100 https://nam10.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.baesystems.com%2F&data=05%7C01%7Charish.radhakrishnan%40ansys.com%7C3858a904b18e44fe460908db146caf89%7C34c6ce6715b84eff80e952da8be89706%7C0%7C0%7C638126229306409132%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=l1JZvfrouKtiEQHHfdg4Q0GvNKcKmzkEO%2FRNGpsisQQ%3D&reserved=0https://nam10.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.baesystems.com%2F&data=05%7C01%7Charish.radhakrishnan%40ansys.com%7C3858a904b18e44fe460908db146caf89%7C34c6ce6715b84eff80e952da8be89706%7C0%7C0%7C638126229306409132%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=l1JZvfrouKtiEQHHfdg4Q0GvNKcKmzkEO%2FRNGpsisQQ%3D&reserved=0

From: AntonisΤ <useratsi98@gmail.commailto:useratsi98@gmail.com>
Sent: Saturday, February 18, 2023 5:53 AM
To: Caba, Aaron C (US) <aaron.caba@baesystems.commailto:aaron.caba@baesystems.com>
Subject: Re: [Xansys] Re: [External Email] FEA/FEM expert

External Email Alert

This email has been sent from an account outside of the BAE Systems network.
Please treat the email with caution, especially if you are requested to click on a link, decrypt/open an attachment, or enable macros.  For further information on how to spot phishing, access "Cybersecurity OneSpace Page" and report phishing by clicking the button "Report Phishing" on the Outlook toolbar.

Okay then.
So basically the problem is this.
I have a honeycomb core and want to analyze its shear properties. Experiments have been done according to the ASTM-C273 standards, which gave us some results about the core. The ones that are of interest to me are the buckling initiation of the walls, the elastic yield point, and the overall shape of the buckled walls. We have the results from the experiments and wanted to move on to creating a FEM/FEA of the same core and see if the model will be in accordance with the experiments.

So I have created a model of the exact core ( Number of cells, material properties) without the loading plates( to save computational cost), the plates have been replaced by boundary conditions where the bottom is fixed on UX,UY, UZ, and the top nodes create a rigid region (cerig Command) with a master node to apply a displacement (as of the experiment which is displacement controlled), MasterNode is fixed in all rotations (ROTZ, ROTY, ROTZ). So far so good, the problem lies when running the model. Currently, I wasn't able to make the analysis results match the experimental ones ( Force vs Displacement curves) because the FEM is much stiffer, almost  3 times, than the actual core.

Another error I get when running the analysis is- excessive element distortion-, this error prevents the analysis from running until the end, my load is 0.5 mm and it stops at 0.06.
[image.png]

Στις Παρ 17 Φεβ 2023 στις 4:01 μ.μ., ο/η Caba, Aaron C (US) <aaron.caba@baesystems.commailto:aaron.caba@baesystems.com> έγραψε:
Antonis,

You haven't provided us anything anyone can act on with your last two posts.  We know you have a problem, but not what it is.  You've given a very general overview of your simulation, so the only thing we could do is give you very general pieces of advice.  No one is going to take the time to guess what your problems are, or play 20 questions. Mohammad tried, but you failed to answer most of the questions he asked.  The impetus is on you to present:  What your problem is; What research you've done to investigate it (google is your friend); What you have tried that has failed AND what has worked; What results you want from this exchange.

I've always found https://nam10.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.catb.org%2F~esr%2Ffaqs%2Fsmart-questions.html&data=05%7C01%7Charish.radhakrishnan%40ansys.com%7C3858a904b18e44fe460908db146caf89%7C34c6ce6715b84eff80e952da8be89706%7C0%7C0%7C638126229306409132%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=wZtCrwePhd2aBwYMvWwQZXPiq%2Fl2fTSSeLsVgM8BU0k%3D&reserved=0 to be a good place to learn how to ask questions on a forum.  It is long, but well worth the read.

Aaron C. Caba, Ph.D.
Sr. Principal R&D Engineer
BAE Systems, Inc.
4050 Peppers Ferry Road, Radford VA 24143-0100 https://nam10.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.baesystems.com%2F&data=05%7C01%7Charish.radhakrishnan%40ansys.com%7C3858a904b18e44fe460908db146caf89%7C34c6ce6715b84eff80e952da8be89706%7C0%7C0%7C638126229306409132%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=l1JZvfrouKtiEQHHfdg4Q0GvNKcKmzkEO%2FRNGpsisQQ%3D&reserved=0https://nam10.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.baesystems.com%2F&data=05%7C01%7Charish.radhakrishnan%40ansys.com%7C3858a904b18e44fe460908db146caf89%7C34c6ce6715b84eff80e952da8be89706%7C0%7C0%7C638126229306409132%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=l1JZvfrouKtiEQHHfdg4Q0GvNKcKmzkEO%2FRNGpsisQQ%3D&reserved=0

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This email has been sent from an account outside of the BAE Systems network.

Please treat the email with caution, especially if you are requested to click on a link, decrypt/open an attachment, or enable macros.  For further information on how to spot phishing, access "Cybersecurity OneSpace Page" and report phishing by clicking the button "Report Phishing" on the Outlook toolbar.

The model is a Honeycomb core that's been tested in shear according to the
ASTM-C273 standards. Test coupons are composed of three parts, the core, the adhesive, and the loading plates. In my model, I removed the plates and used boundary conditions to reduce computational time.
Boundary conditions are: bottom of the core restricted at UX, UY, UZ and at the top I have created a rigid region with a master node to apply the load.
Master node is constrained at ROTX, ROTY, ROTZ.
element type used: Shell181
Loading is displacement control. A displacement is applied at the master node and equally distributed on all nodes of the rigid node.
APDL is the program.

Thanks!

Στις Πέμ 16 Φεβ 2023 στις 1:07 μ.μ., ο/η Mohammad Gharaibeh via Xansys < xansys-temp@list.xansys.orgmailto:xansys-temp@list.xansys.org> έγραψε:

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Hi all,

For what it's worth, the ANSYS constraint equations (I noticed CERIG is used) do not support large displacements (NLGEOM). I am not entirely sure how that would affect this shear problem, but it is probably worth checking up on.
One option is to use bonded contact with a pilot node, as this will support large displacements. I am pretty sure this is what Workbench does for applying remote displacements etc., so the ds.dat file for a simple test problem would provide some help on the syntax, if needed.

Good luck.

Uffe Dal Eriksen
Ramboll Energy, Marine Structures
Denmark

-----Original Message-----
From: Caba, Aaron C (US) via Xansys xansys-temp@list.xansys.org
Sent: 21. februar 2023 22:06
To: XANSYS Mailing List Home xansys-temp@list.xansys.org; xansys-temp-request@list.xansys.org
Cc: Caba, Aaron C (US) aaron.caba@baesystems.com
Subject: [Xansys] Re: [External Email] FEA/FEM expert

It may be a good idea to start with a coarser mesh while you debug your model.  You can learn and experiment a lot more with iterations of 1 minute vs. 60 minutes.

Are you running in large displacement (NLGEOM,ON)? Is your expected load-deflection curve linear or do you expect any non-linear geometric behavior?

Are you sure you are applying your load in the same direction (angle) as your experiment?  The measured stiffness will be a function of the load direction.  This might be another reason to model more of the fixture.  You can make the fixture mesh coarse if you use bonded contact between the face sheet and the fixture without adding much to the runtime.

The excessive element distortion may be due to local buckling in the core.  Maybe run a buckling analysis to see what load the honeycomb starts to buckle.

Like someone else said, increase the number of sub-steps (like 1,000 or 10,000) to see if ANSYS can get 'through' the difficult spot.

Aaron C. Caba, Ph.D.
Sr. Principal R&D Engineer
BAE Systems, Inc.
4050 Peppers Ferry Road, Radford VA 24143-0100 https://eur03.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.baesystems.com%2F&data=05%7C01%7Cude%40ramboll.com%7C9a61d4ee36ae45267dae08db146d520e%7Cc8823c91be814f89b0246c3dd789c106%7C0%7C0%7C638126231983733243%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=eNZoWRv%2Fs8kkS8RT2dJjLY6V49ePL0%2FnamUa2dCgwr4%3D&reserved=0https://eur03.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.baesystems.com%2F&data=05%7C01%7Cude%40ramboll.com%7C9a61d4ee36ae45267dae08db146d520e%7Cc8823c91be814f89b0246c3dd789c106%7C0%7C0%7C638126231983733243%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=eNZoWRv%2Fs8kkS8RT2dJjLY6V49ePL0%2FnamUa2dCgwr4%3D&reserved=0

From: AntonisΤ useratsi98@gmail.com
Sent: Tuesday, February 21, 2023 2:39 AM
To: Caba, Aaron C (US) aaron.caba@baesystems.com; XANSYS Mailing List Home xansys-temp@list.xansys.org; xansys-temp-request@list.xansys.org
Subject: Re: [Xansys] Re: [External Email] FEA/FEM expert

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Okay then.
So basically the problem is this.
I have a honeycomb core and want to analyze its shear properties. Experiments have been done according to the ASTM-C273 standards, which gave us some results about the core. The ones that are of interest to me are the buckling initiation of the walls, the elastic yield point, and the overall shape of the buckled walls. We have the results from the experiments and wanted to move on to creating a FEM/FEA of the same core and see if the model will be in accordance with the experiments.

So I have created a model of the exact core ( Number of cells, material properties) without the loading plates( to save computational cost), the plates have been replaced by boundary conditions where the bottom is fixed on UX,UY, UZ, and the top nodes create a rigid region (cerig Command) with a master node to apply a displacement (as of the experiment which is displacement controlled), MasterNode is fixed in all rotations (ROTZ, ROTY, ROTZ). So far so good, the problem lies when running the model. Currently, I wasn't able to make the analysis results match the experimental ones ( Force vs Displacement curves) because the FEM is much stiffer, almost  3 times, than the actual core.

Another error I get when running the analysis is- excessive element distortion-, this error prevents the analysis from running until the end, my load is 0.5 mm and it stops at 0.06.
[image.png]

Στις Δευ 20 Φεβ 2023 στις 6:43 μ.μ., ο/η Caba, Aaron C (US) <aaron.caba@baesystems.commailto:aaron.caba@baesystems.com> έγραψε:
Antonis,

You just replied to me, not to the list.

• Aaron

From: AntonisΤ <useratsi98@gmail.commailto:useratsi98@gmail.com>
Sent: Monday, February 20, 2023 11:02 AM
To: Caba, Aaron C (US) <aaron.caba@baesystems.commailto:aaron.caba@baesystems.com>
Subject: Re: [Xansys] Re: [External Email] FEA/FEM expert

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Isn't it already posted on the list?

How cad do I post it?

Στις Δευ 20 Φεβ 2023 στις 6:01 μ.μ., ο/η AntonisΤ <useratsi98@gmail.commailto:useratsi98@gmail.com> έγραψε:
Will do. Can you provide any help?

Στις Δευ 20 Φεβ 2023 στις 3:42 μ.μ., ο/η Caba, Aaron C (US) <aaron.caba@baesystems.commailto:aaron.caba@baesystems.com> έγραψε:
Antonis,

That is much informative.  Please post it to the list so everyone can see and heip.

Aaron C. Caba, Ph.D.
Sr. Principal R&D Engineer II
BAE Systems, Inc. | Ordnance Systems, Inc.

E-mail: aaron.caba@baesystems.commailto:aaron.caba@baesystems.com | Mail:  4050 Peppers Ferry Road, Radford VA 24143-0100 https://eur03.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.baesystems.com%2F&data=05%7C01%7Cude%40ramboll.com%7C9a61d4ee36ae45267dae08db146d520e%7Cc8823c91be814f89b0246c3dd789c106%7C0%7C0%7C638126231983733243%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=eNZoWRv%2Fs8kkS8RT2dJjLY6V49ePL0%2FnamUa2dCgwr4%3D&reserved=0https://eur03.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.baesystems.com%2F&data=05%7C01%7Cude%40ramboll.com%7C9a61d4ee36ae45267dae08db146d520e%7Cc8823c91be814f89b0246c3dd789c106%7C0%7C0%7C638126231983733243%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=eNZoWRv%2Fs8kkS8RT2dJjLY6V49ePL0%2FnamUa2dCgwr4%3D&reserved=0

From: AntonisΤ <useratsi98@gmail.commailto:useratsi98@gmail.com>
Sent: Saturday, February 18, 2023 5:53 AM
To: Caba, Aaron C (US) <aaron.caba@baesystems.commailto:aaron.caba@baesystems.com>
Subject: Re: [Xansys] Re: [External Email] FEA/FEM expert

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Okay then.
So basically the problem is this.
I have a honeycomb core and want to analyze its shear properties. Experiments have been done according to the ASTM-C273 standards, which gave us some results about the core. The ones that are of interest to me are the buckling initiation of the walls, the elastic yield point, and the overall shape of the buckled walls. We have the results from the experiments and wanted to move on to creating a FEM/FEA of the same core and see if the model will be in accordance with the experiments.

So I have created a model of the exact core ( Number of cells, material properties) without the loading plates( to save computational cost), the plates have been replaced by boundary conditions where the bottom is fixed on UX,UY, UZ, and the top nodes create a rigid region (cerig Command) with a master node to apply a displacement (as of the experiment which is displacement controlled), MasterNode is fixed in all rotations (ROTZ, ROTY, ROTZ). So far so good, the problem lies when running the model. Currently, I wasn't able to make the analysis results match the experimental ones ( Force vs Displacement curves) because the FEM is much stiffer, almost  3 times, than the actual core.

Another error I get when running the analysis is- excessive element distortion-, this error prevents the analysis from running until the end, my load is 0.5 mm and it stops at 0.06.
[image.png]

Στις Παρ 17 Φεβ 2023 στις 4:01 μ.μ., ο/η Caba, Aaron C (US) <aaron.caba@baesystems.commailto:aaron.caba@baesystems.com> έγραψε:
Antonis,

You haven't provided us anything anyone can act on with your last two posts.  We know you have a problem, but not what it is.  You've given a very general overview of your simulation, so the only thing we could do is give you very general pieces of advice.  No one is going to take the time to guess what your problems are, or play 20 questions. Mohammad tried, but you failed to answer most of the questions he asked.  The impetus is on you to present:  What your problem is; What research you've done to investigate it (google is your friend); What you have tried that has failed AND what has worked; What results you want from this exchange.

I've always found https://eur03.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.catb.org%2F~esr%2Ffaqs%2Fsmart-questions.html&data=05%7C01%7Cude%40ramboll.com%7C9a61d4ee36ae45267dae08db146d520e%7Cc8823c91be814f89b0246c3dd789c106%7C0%7C0%7C638126231983733243%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=3dyCLWUcg12467HB7unPbrJand7xOqqWRzYcFHof%2Bys%3D&reserved=0 to be a good place to learn how to ask questions on a forum.  It is long, but well worth the read.

Aaron C. Caba, Ph.D.
Sr. Principal R&D Engineer
BAE Systems, Inc.
4050 Peppers Ferry Road, Radford VA 24143-0100 https://eur03.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.baesystems.com%2F&data=05%7C01%7Cude%40ramboll.com%7C9a61d4ee36ae45267dae08db146d520e%7Cc8823c91be814f89b0246c3dd789c106%7C0%7C0%7C638126231983733243%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=eNZoWRv%2Fs8kkS8RT2dJjLY6V49ePL0%2FnamUa2dCgwr4%3D&reserved=0https://eur03.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.baesystems.com%2F&data=05%7C01%7Cude%40ramboll.com%7C9a61d4ee36ae45267dae08db146d520e%7Cc8823c91be814f89b0246c3dd789c106%7C0%7C0%7C638126231983733243%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=eNZoWRv%2Fs8kkS8RT2dJjLY6V49ePL0%2FnamUa2dCgwr4%3D&reserved=0

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The model is a Honeycomb core that's been tested in shear according to the
ASTM-C273 standards. Test coupons are composed of three parts, the core, the adhesive, and the loading plates. In my model, I removed the plates and used boundary conditions to reduce computational time.
Boundary conditions are: bottom of the core restricted at UX, UY, UZ and at the top I have created a rigid region with a master node to apply the load.
Master node is constrained at ROTX, ROTY, ROTZ.
element type used: Shell181
Loading is displacement control. A displacement is applied at the master node and equally distributed on all nodes of the rigid node.
APDL is the program.

Thanks!

Στις Πέμ 16 Φεβ 2023 στις 1:07 μ.μ., ο/η Mohammad Gharaibeh via Xansys < xansys-temp@list.xansys.orgmailto:xansys-temp@list.xansys.org> έγραψε:

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Classification: Confidential

Hello,

I have tried all those methods to get a result but nothing worked. I can
agree that removing the loading plates may be affecting the results but in
reality, the plates are bonded to the core in a way that creates a rigid
region. The core will fail (be cut in half) and still be bonded with the
plates, so I wouldn't say for sure that this is the cause of the problem.

This problem have really troubled me and still I cannot find the answer.

Antonis
University of Athens, Mechanical Engineering

Στις Τετ 22 Φεβ 2023 στις 9:48 π.μ., ο/η Uffe Dal Eriksen via Xansys <
xansys-temp@list.xansys.org> έγραψε:

Hello all,

Your problem seems to be non-linear with excessive deformation.

I would suggest to go for explicit solver (if possible). You won't face any convergence issue, rather you have to take care in specifying dT (time step). You can refine your model and eventually solve a Quasi-static simulation.

Disclaimer:  I may be completely wrong. :-)

Thanks
Anjum

-----Original Message-----
From: AntonisΤ useratsi98@gmail.com
Sent: 22 February 2023 13:37
To: XANSYS Mailing List Home xansys-temp@list.xansys.org
Subject: [Xansys] Re: [External Email] FEA/FEM expert

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Hello,

I have tried all those methods to get a result but nothing worked. I can agree that removing the loading plates may be affecting the results but in reality, the plates are bonded to the core in a way that creates a rigid region. The core will fail (be cut in half) and still be bonded with the plates, so I wouldn't say for sure that this is the cause of the problem.

This problem have really troubled me and still I cannot find the answer.

Antonis
University of Athens, Mechanical Engineering

Στις Τετ 22 Φεβ 2023 στις 9:48 π.μ., ο/η Uffe Dal Eriksen via Xansys < xansys-temp@list.xansys.org> έγραψε:

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