Determining the Yield strength and Ultimate tensile strength of HDPE

• Mar 20, 2022

• #1

Anmol Dubey

15

1

TL;DR Summary

Apparently yield strength cannot be greater than ultimate tensile strength but in my graph the yield strength is greater
Trying to determine the yield and ultimate tensile strength

Help would very appreciated. Also I am new to this website so if something seems wrong please tell me :)

 

Attachments

• HDPE.pdf

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• Mar 20, 2022

• #2

jrmichler

Mentor

2,213

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Tell us something about your test setup, the material under test, and what you observed during the test. Also, it helps to post the full image - save as a JPG, click Attach Files >> Insert >> Full Image.

 

• Mar 20, 2022

• #3

Anmol Dubey

15

1

jrmichler said:

Tell us something about your test setup, the material under test, and what you observed during the test. Also, it helps to post the full image - save as a JPG, click Attach Files >> Insert >> Full Image.

The substance being tested is Polyethylene. I have uploaded a picture of the fracture and the graph as jpg

 

• Mar 20, 2022

• #4

Anmol Dubey

15

1

Anmol Dubey said:

Summary:: Apparently yield strength cannot be greater than ultimate tensile strength but in my graph the yield strength is greater
Trying to determine the yield and ultimate tensile strength

Help would very appreciated. Also I am new to this website so if something seems wrong please tell me :)

 

• Mar 20, 2022

• #5

jrmichler

Mentor

2,213

2,947

I did a quick search using terms stress strain curve polyethylene. The first hits discussed strain softening, strain rate, and the effect of temperature. The plot below shows the effect of strain softening. It's the portion of the stress strain curve from a to c.

Also, polyethylene comes in many forms - some of which are LDPE, medium density, HDPE, UHMWPE. They have large differences in material properties. I suggest that you do some searching of the material properties of your type of polyethylene and also polymers in general. Pay special attention to strain softening.

 

• Mar 20, 2022

• #6

Anmol Dubey

15

1

jrmichler said:

I did a quick search using terms stress strain curve polyethylene. The first hits discussed strain softening, strain rate, and the effect of temperature. The plot below shows the effect of strain softening. It's the portion of the stress strain curve from a to c.
View attachment 298696
Also, polyethylene comes in many forms - some of which are LDPE, medium density, HDPE, UHMWPE. They have large differences in material properties. I suggest that you do some searching of the material properties of your type of polyethylene and also polymers in general. Pay special attention to strain softening.

Could you please tell me where the UTS and Yield stress would be on my graph?

 

• Jul 5, 2022

• #7

Jodo

32

95

The first peak on the graph is the yield point. UTS is normally higher then the yield stress. Is it possible the sample slipped in the "grips" during the tensile test?

 

• Feb 7, 2023

• #8

ahmasrieng

1

0

I have the same problem exactly, can anyone advise me?

 

• Feb 7, 2023

• #9

berkeman

Mentor

66,802

19,441

ahmasrieng said:

I have the same problem exactly, can anyone advise me?

Welcome to PF.

After reading the responses above, what questions do you still have? Can you upload your test results (use "Attach files" below the Edit Window) and tell us what you think your problem might be? Thanks.

 

1. What is the difference between yield strength and ultimate tensile strength?

Yield strength is the amount of stress a material can withstand without permanent deformation, while ultimate tensile strength is the maximum stress a material can withstand before breaking.

2. How is the yield strength of HDPE determined?

The yield strength of HDPE is typically determined through a tensile test, where a sample of the material is pulled until it reaches its yield point. The yield strength is then calculated by dividing the maximum load applied during the test by the original cross-sectional area of the sample.

3. What factors can affect the yield strength of HDPE?

The yield strength of HDPE can be affected by factors such as temperature, strain rate, and the presence of any additives or fillers in the material. Additionally, the manufacturing process and any external stresses on the material can also impact its yield strength.

4. How is the ultimate tensile strength of HDPE measured?

The ultimate tensile strength of HDPE is measured through a tensile test, similar to the one used for determining yield strength. However, in this test, the material is pulled until it breaks and the maximum load applied at the point of failure is recorded. The ultimate tensile strength is then calculated by dividing this load by the original cross-sectional area of the sample.

5. Can the yield strength and ultimate tensile strength of HDPE be improved?

Yes, the yield strength and ultimate tensile strength of HDPE can be improved through various methods such as adding reinforcing fibers, increasing the molecular weight of the material, and using specialized manufacturing techniques. However, these improvements may also affect other properties of the material, so careful consideration is needed when making modifications to HDPE.