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Stress-strain-curve - Material properties at a glance

Stress-strain curve is my favorite graph since it offers so much valuable information on any plastic material at a glance. Unlike many other graphs, stress-strain-curves are also easy to find.

The tensile test for drawing the curve is presented in this video.

What happens during the test is aptly described in this Univesity of Cambridge animation.

The curve delivers a lot of information. To summarize:

 

Another important material property that Stress-strain curve illustrates is toughness. This is described in a separate article that you can find here.

Does the stress-strain curve always look the same?

The look of the curve depends of the material. Here are three typical material types and their curves.

 

  • Curve B could illustrate the properties of some unfilled engineering plastic; PA for instance.
  • Curve A is typical for brittle and stiff material, for example PS. There is no plastic area. The specimen breaks at the end of its elastic area. The pieces fit perfectly to each other.
  • Curve C could follow the behavior of some soft TPE grade. It is hard to say where the elastic area ends. The elongation might be several hundred percent.

It is easy to see a great deal of not only the mechanical properties but also the nature and feel of a material in the curve.

These were the basics...

...there is more to it.

The curves above described material properties in a certain temperature and with a specific loading rate. As we know, the mechanical properties of polymers are highly dependent on service temperature. But it is more rarely known that loading rate has a significant effect on their behavior as well. I’ll return to this with an article soon. Stay tuned and follow the blog in facebook or LinkedIn.

Comments

Subbu
I really appreciate your work Markus, Kudos to that ! keep up the good work
Markus Paloheimo
Thank you Subby, I must activate myself on this for change...
vivek
thnks for this details i like this before it i can never seen comparison between the materials in polymer
Markus
Hello Ashish, Stress-strain curve illustrates material behaviour. It is done using specified specimen. You can stress some component and see how much it yields and under what load it breaks. This information might be useful and you can use this as quality criteria. But it is not the same test. Geometry has a big influence on the results. Markus

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