×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• 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.

# How to constrain the surface to be traction free?

## How to constrain the surface to be traction free?

(OP)
Hi Everyone,

I want to specify certain stress components to be zero at some surfaces.  So I tried Loads -> Surface traction -> Magnitude=0 in the Edit Load dialog box.  I got the error message "Load must be created with a non-zero magnitudes unless utilizing a user subroutine".

Is there any easy way to make certain stress components at the surface remain zero throughout the anaysis?  Thanks!

### RE: How to constrain the surface to be traction free?

A surface is traction free as long as you do not apply external tractions on it.

If you check the stress components, with respect to the surface, (extrapolated) at the nodes they should be very close to zero if the material is elastic.

If the material undergoes permanent deformation near the surface then these stresses might have a small value (but higher than for the elastic material) in general due to high stress gradient in the elements near the traction free surface.

### RE: How to constrain the surface to be traction free?

(OP)
Thank you, xerf.

This is a composite material and I applied uniform deformation boundary condition.  Therefore unwanted stress components develop at the surface due to the underlying heterogeneous structure.  I want to constrain these unwanted stress components to be zero so that I can use Hook's law to calculate average elastic properties of the composite.

I want to specify a certain stress component to be zero all the time during the analysis.  But I don't know how to do this.

### RE: How to constrain the surface to be traction free?

In a 3D model at a free surface with no applied loads or supports the only zero stress component is the one normal to the surface. Since static FE analysis is basically the solution of F=k.x , the user can only have control of the force applied (F) and displacement (x).

### RE: How to constrain the surface to be traction free?

if a surface is traction free and one decompose the zero traction vector into the normal component and the shear component , and the normal component is the only zero component then....
....how about the shear component on the surface ?

### RE: How to constrain the surface to be traction free?

3D solid elements in general produce 3 principal stresses at their nodes. At a free surface one of these principal stresses is zero (or at least very close to zero compared to the other two) in the direction normal to the surface. The system of stresses then simplifies to a 2D stress system. Depending on the geometry and the nature of the loading one of the in plane principal stresses may also be zero.

#### 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.

#### 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
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™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:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!