Elongation at Break

[AirRider04]

I have two materials

Mat'l 1 Yield = 70300psi
Ultimate = 84800psi
Elongation = 14%

Mat'l 2 Yield = 76500psi
Ultimate = 86000psi
Elongation = 26%

If i substitute Material 2 for material 1, what impact will the higher Elongation have?

Thanks

 

[metengr]

Typically, elongation is a measure of ductility in metals. Assuming the elongation was measured using the same gage length for both materials, material #2 will absorb a greater amount of plastic deformation (or permanent strain) in comparison to material #1, prior to fracture.

 

[israelkk]

Work is force x displacement. Since both materials have approximately the same ultimate strength the force to break them is the same. However, the deflection to break of material 2 is 26/14 ~ 2 compared to material 1 therefore, the work for break is approximately double.

 

[CoryPad]

To add to [blue]israelkk[/blue]'s fine answer, work equals energy, so material two will absorb twice the energy. Some people relate more to energy...

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[AirRider04]

Thanks for the help

 

[Maui]

It depends upon the application. If the part is loaded so that the resulting stresses are within the elastic region, then the greater elongation of material #2 will have no discernable impact at all. To give you an idea of what these various material properties are used for, the tensile strength is used to assess the quality of the material. It is generally not used in design for ductile materials because by the time the UTS has been reached there has already been a great deal of plastic strain. But it is a good indication of harmful inclusions or flaws. If a bar contains these defects, it will not reach the same maximum stress as a bar of higher quality material. The percent elongation at fracture can be an even better index of quality than the tensile strength because if inclusions or porosity are present, the elongation is drastically lowered.


Maui

 

[NickE]

Also I think (and I may not be right) that a material with a higher elongation and the smae strength levels will resist impact failure better. (IE absorb more energy before break as Iraelkk said)

Nick
I love materials science!

 

[gthelen]

Airrider 04,

I have problems with the results you have:
Mat'l 1 Yield = 70300psi
Ultimate = 84800psi
Elongation = 14%

Mat'l 2 Yield = 76500psi
Ultimate = 86000psi
Elongation = 26%

You have a 14KSI difference between Yield and tensile and 14% elongation.

Mat'l 2 has a 10K Difference and the elongation is twice as much. This is unusual for most materials. The higher the Yield/Tensile ratio is the higher the elongation should be. Have someone check the values again and make sure they use the correct starting Gage length.

GThelen

 

[SMF1964]

NickE: I'm not sure that impact strength will be better, but the greater elongation suggests a greater toughness and flaw tolerance.

GThelen: Are you assuming that the same material is involved here (as in two steels or two copper alloys)?

 

[gthelen]

Err thanks,

True, did not think 2 different matl's.

Gthelen