1018 carbon steel tensile test explanation

In summary, the experimental setup was not correct, and the data was not correct. The large difference in the graphs suggests that the data was not from error in the calculations, but from a difference in the samples.
  • #1
Jacob Noble
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TL;DR Summary
Tensile tested 2 samples of 1018 unheat treated carbon steel, assumed to be very similar steel (bought from same place, same order, ect) very different tensile test results.
Tensile tested 2 samples of 1018 unheat treated carbon steel, assumed to be very similar steel (bought from same place, same order, ect) but very different tensile test results.
The results of the tensile test can be seen below as well as a few calculated values. I do not know what this would be from as the samples were tested on same machine with changing settings (re balanced), one after the other, measurements taken from same spots.
Screenshot (18).png
 
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  • #2
Raw data for both test
 

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  • #3
For starters, your numbers are completely wrong for any type of steel. AISI 1018 steel could have a yield somewhere near 50 KSI if is was cold rolled, but a yield stress of 50 MPa (7.25 KSI) is not steel. A strong plastic, maybe, but not steel. Similarly, a yield strain of 0.04 is way beyond any steel on this planet.

Go back and take a long hard look at the experimental setup. How is the force and strain measured? Has the equipment been calibrated? Recheck every step of your calculations. And add units to the labels in your spreadsheet.
 
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  • #4
I was off by a factor of 10 for stess in my calculations. So 500 not 50 MPa.
The units are now fixed but still the large problem of difference in the graphs.
The difference was also immediately noticed when testing by the automatic graphing the testing program has, meaning it did not come from error in my calculations.
 
  • #5
All carbon steel has the same elastic modulus, and that modulus is linear. When two different samples of similar steel show different elastic moduli, and one of those is curved, the experimental setup is suspect. Please reread the rest of my post with that in mind.

When the labels in your spreadsheet are confusing, or flat wrong (stress vs strain), readers can easily get the idea that you rushed the process without thinking about what is being done. The fact that a specimen was loaded into a machine, a button was pushed, and data output, does not mean that the data is correct. Given what you have showed us, I suggest that you spend several hours studying the machine, and asking yourself what could go wrong. That includes studying the owner's manual in detail.

Hint: If the strain was measured with an extensometer, those are subject to a number of errors. Pretend that you have an exam tomorrow on error sources in the entire setup - test machine, data reduction, strain measurement, force measurement, etc.

Another hint: When I said "several hours", I was being conservative, not facetious. Expect to take longer than that if you want to do it right.
 
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1. What is 1018 carbon steel?

1018 carbon steel is a type of low carbon steel that contains approximately 0.18% carbon. It is commonly used in a variety of industries due to its high strength and good machinability.

2. What is a tensile test?

A tensile test is a type of mechanical test used to determine the strength and ductility of a material. It involves pulling a sample of the material until it breaks, and measuring the amount of force required to do so.

3. Why is a tensile test performed on 1018 carbon steel?

A tensile test is often performed on 1018 carbon steel to determine its mechanical properties, such as its yield strength, ultimate tensile strength, and elongation. This information is important for engineers and manufacturers to ensure the steel is suitable for its intended use.

4. How is a tensile test performed on 1018 carbon steel?

During a tensile test, a sample of 1018 carbon steel is placed in a testing machine and pulled until it breaks. The force applied and the resulting elongation of the sample are recorded. These values are then used to calculate the mechanical properties of the steel.

5. What is the significance of the results from a tensile test on 1018 carbon steel?

The results from a tensile test on 1018 carbon steel can provide valuable information about the material's strength, ductility, and overall quality. This information can be used to determine if the steel is suitable for its intended application and to make any necessary adjustments to the manufacturing process.

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