BREAK FORCE FOR DIFFERENT TEMPERATUREs

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• Last Post 12 October 2018
Adisa posted this 12 October 2018

Hi,

I am trying to do analysis for two different temperatures. I  attached  file the analysis of the beam where I need to do the breaking force . Also I attached the data file and excel of the used material. I am doing analysis of beam with with PA GF 30  at -40 and 23 C. I used the eng. stress and strain, did not convert to true, I know that need to that convergence, now we will ignore that.

At -40, the curve  eng. stress and strain  has brea point, it is when the construction will separate.

At 23, the curve eng. stress and strain has yield point. It is when on the construction will appear the cracks, total strain bigger than total strain at yield.

Now, I am interested how to find find force of breaking (separating, not only craks) at these two temeperatures.

The points break and yield point on the curve are not same?

Breaking point for -40C  is 257 MPa and 4%; for 23 C is 195 MPa and 3,5%.

If I put that these are the same points, I will get the break force of -40 is bigger than at 23. Now I am interested how to find the break force (separating) at 23 and -40.

Can anyone chack the excel file and ansys file (18.2), are those ok.

Does anyone has the curve stress strain of PA GF 30, where has point after yield point at temperature 23 (break point). And that do comparing the break force at -40 and 23.

Attached Files

Adisa posted this 12 October 2018

For example, this the curve has breaking point, and we can  assume that the construction will break (separation, not only crack) at total strain bigger of 65%?

peteroznewman posted this 12 October 2018

I advised you in this post that you should use Conditioned properties and not the Dry properties for molded plastic. I repeat that advice now.

You should read this to learn about the difference between dry and conditioned parts.
You seem to have taken the data from the dry condition, but that is not representative of parts in use.

From the attached pdf, the Elongation value is 8% where kond. means conditioned.

Here is that same data in English from CampusPlastics.com.  Note the large difference in these three values between dry and conditioned.

Campus Plastics is brilliant because they give you the Stress-Strain curve data points in Excel, you don't have to digitize!

In normal use of molded plastic parts, the Conditioned properties apply.
Dry properties are only valid for a few hours after molding.
Please explain why you think using Dry properties is appropriate.