Elongation at break vs Yield Strength vs Tensile Strength 2

[CR100]

We have recently done some material strength test and have run into an interesting situation. This has caused to reevaluate if we totally understand the relationship between yield & tensile strength and elongation at break.

In Sample #1, the properties are,

YS = 160ksi
TS = 196ksi
Elongation at break = 12%

Sample #2

YS = 303ksi
TS = 310ksi
Elongation at break = 12%

I was under the assumption that Yield strength played a critical role in the elongation at break, but from the two samples it does not. As well I thought perhaps the tensile strength and toughness would influence the elongation at break but this is not the case either.

My questions is can you base the elongation at break based on the yield and tensile strength. In this example, no you cannot. So what properties determine the elongation at break?

 

[EdStainless]

What is the reduction in area at the fracture?
Can you measure elongation dynamically during the test?
Have you carefully looked at each sample for external reasons (inclusions, surface defects, notches)?

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[arunmrao]

Assume that both the test samples are from the same stock.If that is true,then you must closely look at the inhomogenities or any machining marks in the test samples to get such a variance. Also were the two tested by the same operator. I once had an interesting experience on a Hounsfield tensometer,where the zero was not set and misleading results obtained.

Learn the rules,so you know how to break them properly.
Dalai Lama

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[metengr]

Not sure of the OP question. Are you asking if you can predict elongation based only on tensile strength properties without elongation or reduction of area?

No.

If you have different strength levels of the same heat of material from different heat treatment, the answer is still no.

The only way to predict strain at fracture is to obtain the strain hardening coefficient or run a tensile test as you did.

 

[tbuelna]

CR100,

Although I can't answer your specific question, I'd suggest that you ignore that second set of test data. You won't get a combination of 310KSI UTS and 12% elongation in any alloy that I know of (including multi-phase or Aermet).

Regards,
Terry

 

[CR100]

The materials were from different stock, in this case it was two different shafts.

The real point of the question was to really look at what is important in choosing a shaft material. The elongation at break or the toughness (UTS - YS). I know the toughness equation isnt totally accurate.

The materials of sample 1 was 1524 and the of sample 2 was maraging 300.

 

[metengr]

CR100;
As I suspected. Most shaft design calculations involve allowable stress in terms of yield strength (you don’t want to distort the shaft in service) for tensile, shear and bending loads, followed by tensile strength for evaluating high cycle fatigue strength.

Toughness would be important if the shaft is subjected to dynamic loading conditions, and tolerance for flaws. Strain to fracture is not really used for shaft design.

 

[CR100]

Metengr, in our situation there is dynamic loading, so toughness is very important. But I was looking for a correlation between toughness and elongation at break.

But comparing sample 1 and 2, sample 2 UTS-YS= 7 ksi, while sample 1 UTS-YS=36ksi. While both samples had identical elongation at break. Which puzzles me. I would expect the sample 2 elogation at break to be much lower than sample 1.

 

[metengr]

CR100;
As an approximation, the area under the tensile stress/strain curve will give you some idea of material toughness (the larger the area and greater the toughness) but this approach should not be used in design. Instead, you should obtain fracture toughness values or perform Charpy V-notch testing to determine if you have adequate toughness for the intended service conditions.

 

[TVP]

CR100,

1524 and maraging 300 steels do not have the same microstructure, so they will not necessarily produce similar strength-ductility relations. For medium carbon martensitic steels (say 0.20-0.45% C) that are tempered at the same temperature and produce essentially the same strength/hardness, the elongation/fracture strain should be similar. 1524, 4130, and 5135 would produce similar elongation when quenched and tempered to ~ 190 ksi tensile strength, meaning in the range of 8-15%.

Maraging steels are different: they have a low-carbon martensite structure, which means that the normal martensite laths that are tempered into extremely fine carbide particles are not really present in maraging steels. These steels are more like precipitation hardening stainless steels in terms of microstructure, which means that they have higher elongation for a given tensile strength than conventional martensitic steels. Also, they are usually produced by vacuum arc remelting (VAR) or electroslag remelting (ESR), which has fewer inclusions and also improves ductility. The following links have additional information on this subject:

http://www.latrobesteel.com/assets/documents/datasheets/Marvac_300.pdf

http://www.buehler-asia.com/brochure/apps_support-tech-notes_vol3iss7-tn37.pdf

http://www.everyspec.com/MIL-HDBK/MIL-HDBK+(0001+-+0099)/MIL_HDBK_5J_139/