# 0.2 percent offset for computing the yield point

• svishal03
In summary, the conversation discusses the process of computing the yield point for an experimental true stress vs true strain plot of a metal. The individual took initial points on the curve and fitted a straight line to determine the elastic part of the curve. They then constructed a parallel line to this straight line to find the yield point, which they estimate to be around 1500 MPa. However, the offset method gave a yield point of 1235 MPa, causing confusion. The conversation also mentions the material being tested and the need for more information.
svishal03
I need to compute the yield point for an experimental true stress vs true strain plot of a material as attached in the screenshot.

See attached;

I have true stress vs true strain plot. I took some initial points on the curve and fitted a straight line which gives me the elastic part of the curve.

I constructed a line parallel to this straight line (parallel line has same slope as straight line, I got the constant of y = mx + c of the parallel line by putting x =0.002 when y = 0).

But from the graph it is evident that yield point is around 1500 MPa but the offset method gives me a yield point around 1235 MPa.

Please can anyone suggets/help what is going wrong?

#### Attachments

• 0_pt_2_percent_offset.JPG
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svishal03 said:
But from the graph it is evident that yield point is around 1500 MPa but the offset method gives me a yield point around 1235 MPa.

Why is it evident it occurs at 1500 MPa? It seems to me that 1500 MPa is approximately 2% yield (if the units on the x-axis are decimal percentages). Remember that 0.2% yield is a pretty small deviation from the linear region.

What material are you testing?

The units on x-axis are not percentages.

I say that it is evident that yielding occurs at 1500MPa. because at yielding material just flows.

We can also say that one gets yield point by joining origina with breaking point (this getting a line) and then drawing a line parallel to this line such that the line drawn parallel is tangent to the stress strain curve.This point where the parallel line is tangent is the yield point (http://composite.about.com/library/glossary/y/bldef-y6168.htm).

From the graph it looks that 'flowing' occurs at around 1500MPa definitely not 1235

The material is a metal

svishal03 said:
The units on x-axis are not percentages.

OK, so it's strain then.
svishal03 said:
I say that it is evident that yielding occurs at 1500MPa. because at yielding material just flows.

The 0.2% yield number is meant to be the boundary of the material's linear elastic region. I would say the material is well into the yield region by 1500 MPa, because there is significant (to the eye) plastic deformation occurring. If you loaded the sample to 1500 MPa and then released, you would see permanent deformation after just one cycle.

svishal03 said:
From the graph it looks that 'flowing' occurs at around 1500MPa definitely not 1235

Be that as it may, it looks to me like there is significant plastic deformation by 1500 MPa, so I would say your estimated 0.2% offset is correct.

svishal03 said:
The material is a metal

OK, well that's not very helpful. Whatever it is it's pretty strong stuff with yield in the 1235 MPa regime (chromoly steel maybe?) I ask because it would be nice to be able to compare published values to your calculated value and see if you're in the ballpark...

You really should make the pic show more about the elastic area. No need to have the strain go up to 0,5 if you're studying the area of up to 0,005 or something.

## What is the purpose of using 0.2 percent offset for computing the yield point?

The 0.2 percent offset method is used to determine the yield point of a material, which is the stress level at which it begins to exhibit plastic deformation.

## How is the 0.2 percent offset method applied?

The method involves applying a small, constant offset strain (usually 0.2 percent) to the material and plotting the stress-strain curve. The yield point is then determined as the intersection of the offset line and the stress-strain curve.

## Why is the 0.2 percent offset method commonly used?

This method is commonly used because it provides a consistent and standardized way of measuring the yield point, which is important for comparing the strength of different materials.

## Can the 0.2 percent offset method be used for all materials?

No, this method is most suitable for materials that exhibit a distinct yield point, such as metals. Materials that do not have a clear yield point, such as polymers, may require alternative methods for determining their yield strength.

## Are there any limitations to the 0.2 percent offset method?

One limitation of this method is that it assumes a linear relationship between stress and strain, which may not be accurate for all materials. It also does not take into account any strain hardening that may occur after the yield point.

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