basic Stress Strain ?

[sydneyjongleur]

Hi,

This is a very basic question on stress strain so I am hoping that I will find the answer.

I have conducted a tensile test and have the load values in Newtons.

I want to plot the results in stress/ strain graph

I have calculated the different engineering stresses with the formula:S= load/ cross sectional area.

Then I have calculated the strain- e= change in length/original length.

The issue that I have( and I maybe missing the point here)is that I have various values for stress but only 1 value for strain ie 0.3. So how do I plot the different values for stress against 1 value for strain.

Do I have to carry out a calculation which includes the elasticity modulus to get different strain values?

I then have to calculate the true stress/ strain when I have carried this out.

 

[salmon2]

First of all, familiarize with engineering stress/strain and true stress/strain.

Then do you have the curve of load vs displacement from you tensile test? If yes, plot of engineering stress/strain is very straightforward, just use original cross section and length.

Based on engineering stress/strain curve, in theory, you can Plot out true stress/strain, at least until necking happens. After necking, it is not correct any more because loading is not axial, but a tri-state stress.

 

[TVP]

Sydney,

If I understand your post correctly, you have many stress measurements, but only 1 strain measurement, i.e. the strain to failure which is 0.3? You have to continuously measure the strain during the test in order to create a stress-strain plot. Strain is measured using an extensometer, or by using the cross-head displacement.

http://www.instron.us/wa/solutions/astm_e8_tension_testing_metallic_materials.aspx

http://www.instron.us/wa/services/calibration/displacement.aspx

http://www.epsilontech.com/faq.htm

 

[metengr]

What you can do is plot engineering stress values as you have obtained versus engineering strain calculated from the elastic modulus up until 0.2% offset. This is about all you can do with the data you provided. Unless you have determined strain values beyond the stated offset value, the 0.3 is one data point.

http://www.keytometals.com/Articles/Art43.htm