×
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

# relation between viscosity/relaxation time on KBK-Z model and temperature.

 Forum Search FAQs Links MVPs

## relation between viscosity/relaxation time on KBK-Z model and temperature.

(OP)
Hi,

I am simulating the blow-moulding process based on injection using ANSYS Workbench Polyflow Module.
I am doing a viscoelastic isothermal analysis, and I am using the KBK-Z model for viscoelasticity. The inputs are Viscosity and respective relaxation time.

I know that temperature does not exist on this analysis. However, I would like to estimate the temperature at which PET has this spectrum shown next:

Mode Viscosity (Pa-s) Relaxation time (s)
1 1E+04 0.01
2 3E+04 0.1
3 1E+05 1

Or, even better, how can I calculate it? There is any way?

Best regards,
AndradeLopes

### RE: relation between viscosity/relaxation time on KBK-Z model and temperature.

Have you looked at the WLF equation?

Rick Fischer
Principal Engineer
Argonne National Laboratory

### RE: relation between viscosity/relaxation time on KBK-Z model and temperature.

(OP)
Hi,

Yes, I know the Williams-Landel-Ferry equation. But I don't know how to use it for this specific problem. Could you please detail a possible approach?
Is it valid for the KBK-Z model? How can I relate the two?

What are the values of u0, C1, C2 and Tr for PET in a temperature lower (but not much) that it's melting point, 70%, let's say?

Do I need to do experimental tests, in order to build a master curve? Is there any online resource with the experimental data needed to obtain the parameters and to solve the equation?

I am attaching the equation, and I ask you please to confirm if this is the correct equation.

Thank you for your replay,
Best regards,
AndradeSilva

### RE: relation between viscosity/relaxation time on KBK-Z model and temperature.

This is pretty basic stuff. Get a good text like Into to Physical Polymer Science by Sperling and study up

ln(n/nr) = -C1(T-Tg)/(C2+(T-Tg) where n=viscosity, ng = viscosity at Tg, T is temp, and Tg is the glass transition temp. For Pet, C1=39.12, C2=51.6 for many polymers, ng is approximatly 1e13 poise.

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 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!

Already a member? Close this window and log in.