×
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

Failure Criterion For Polymers ?

Failure Criterion For Polymers ?

Failure Criterion For Polymers ?

(OP)
I would like to find the appropriate failure criterion for polymer materials. Von Mises is typically the accepted criterion for ductile metals, but for plastics I have read in many cases it is not accurate. The polymers I am most interested in are : ABS, Acrylic, SAS, HDPE, LDPE, and PC. Would appreciate any info on any of these materials or if you could point me to a source for information.

RE: Failure Criterion For Polymers ?

There's a nice explanation here: https://www.youtube.com/watch?v=Smj_F7MN3S4

For ductile materials take the yield strength and for brittle materials take the ultimate tensile strength. You can find values for all the plastics you mentioned for free at matweb.com

Having said that the actual "failure criterion" for polymers is far more complex. Failure could happen due to exposure to sunlight or chemicals. It could happen due to impact. It's important to consider how your part will be used and what constitutes a failure for you.

Chris DeArmitt PhD FRSC
President

Plastic materials consultant to the Fortune 100
Creating New Materials - Problem Solving - Innovation Keynotes - Expert Witness
www.phantomplastics.com

RE: Failure Criterion For Polymers ?

This is not as straight forward as it sounds. For instance, yield in some polymers can be better modeled with the Extended Drucker Prager model. This takes into account the dependency of yield strength on the hydrostatic stress state. The idea is that an increase in the dilatational stress component increases free volume, thereby increasing chain mobility and reducing the yield strength. All very nice, but you need special material properties to use this model and these are not commonly available. Unless you want to invest money in testing, you are stuck with common data sheet allowables and common failure criteria.

Yes as Chris pointed out, this can get hairy. Strain rate, ambient temp, environmental factors are all a concern. Creep of course is an issue with continuous loads, and fatigue analysis in plastics is like herding cats. Plus, the materials you listed are hugely dissimilar, so what works for one may not work for the other. If you want to do some reading, I suggest the following:
Failure of Plastics by Browstow and Corneliussen
Structural Analysis of Thermoplastic Components by Trantina and Nimmer
Fracture Behaviour OF Polymers by Kinloch and Young
Deformation and Fracture Mechanics of Engineering Materials, Chapter 6, by Hertzberg

Rick Fischer
Principal Engineer
Argonne National Laboratory

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