×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

ABAQUS - Energy balance of implicit simulation including cohesive element

ABAQUS - Energy balance of implicit simulation including cohesive element

ABAQUS - Energy balance of implicit simulation including cohesive element

(OP)
Hi all,

I am having trouble with my 2D simulation work, therefore, hope there is anyone who can help me with this.

To briefly explain my model, I am working on the penetration of the hyperelastic body. The rigid body is piercing the soft matter along the predetermined crack path where cohesive elements are assigned.
However, the energy outputs do not seem to satisfy the energy balance condition.
The simulation is a quasi-static analysis with a dynamic implicit step. Since the friction is ignored in my model, the energy balance equation can be simplified as follows:

ETOTAL = ALLKE + ALLIE - ALLWK , where ALLIE = ALLSE + ALLDMD + ALLAE

with other outputs zero.

As it is shown in the attached file, when the penetration begins (cohesive element starts to fail), a discrepancy between external work and internal energy occurs and total energy becomes negative...
I am currently guessing this is caused by some errors when cohesive elements are included in the crack propagation problem.

Does anyone know why this kind of problem I am facing?
When I checked the slope of ALLDMD - Crack length plot, it was only half of the fracture toughness I assigned for the cohesive element (thickness is 1). I couldn't understand why I get this result...

I would appreciate any help or idea.

Details of model:
*Dynamic implicit (quasi-static)
*Soft matter: NH model
*Cohesive element: bilinear cohesive law
*Zero thickness cohesive elements are tied with soft bodies, rigid body is inserted along the crack path
*Interaction property: Normal (hard contact), Tangential (frictionless)
*Displacement B.C. assigned to rigid body (ramp)

RE: ABAQUS - Energy balance of implicit simulation including cohesive element

Do the contour plots on the deformed shape of the model look reasonable ? Please attach pictures showing them, if it’s not a problem. Is this analysis based on some research paper ? If yes, can you share the title ?

Apart from checking for errors in the current analysis, you may have to try a slightly different approach, for example with cohesive contact.

RE: ABAQUS - Energy balance of implicit simulation including cohesive element

(OP)
Hello, @FEA way

I guess the contour plots seem reasonable. The analysis is based on the paper "Detailed finite element modelling of deep needle insertions into a soft tissue phantom using a cohesive approach".

Do you know if the total energy is generally constant throughout the crack propagation simulation with simple loading such as pure shear fracture when cohesive elements are included?

I just want to know if this is an inherent error related to the cohesive elements before moving on to try different methods...

RE: ABAQUS - Energy balance of implicit simulation including cohesive element

Request output of all the energies available for this analysis (*Energy output, variable=all) then plot them all (together, in various combinations and one by one). There’s a great chance that you will find the cause of the problem this way.

If we take a closer look at the available energies, here’s more or less what we get for the end of the analysis (ignoring energies that are almost zero):

ETOTAL = ALLIE - ALLWK
ALLIE = ALLSE + ALLDMD

ALLIE = 0.1 + 0.35 = 0.45
ETOTAL = 0.45 - 0.55 = -0.1

So you can probably narrow down your focus to those 3 energies instead of looking at ETOTAL.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close