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Stress-strain curve i am working with

This stress-strain curve presents a linear elastic range, followed by yielding and accompanied by a decrease in toughness the material goes into the plastic region. As it strains more and more the material then suddenly snaps! Without necking...

Fracture occurring without necking isn't something I would expect from a ductile material, in fact it's a trait of a brittle material. But, the material can't be brittle with all that strain in the plastic region.

So which is it? Question: Would this material fall into a "mostly ductile" category instead of ductile?

I have four stress-strain curves i am working with at the moment. Three of them are similar to this one however, they show a decline in stress when necking before fracture. This diagram does not decline in stress before fracture. They were all tested on the same tensile stress machine (a Shimadzu machine i believe). Part of the assessment is to determine the possible types of materials each curve could be.

Question: Because this material doesn't neck so i'm wondering if there are any materials which have a stress-strain curve such as this. I was thinking some metals may strain and then just snap or perhaps timber. I'm really not sure.

Zantheor
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user6462
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2 Answers2

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The diagram is representing true stress, as opposed to the engineering stress. So as not to copy-paste, see my answer to a related question for a description of these different stress measurements. Basically, true stress takes into account the reduced cross-sectional area due to necking, therefore the stress measurement never drops. Meanwhile, engineering stress considers the original area throughout the test, even though necking has reduced the actual area, leading to a reduction in the apparent requisite stress to further deform the member.

Community
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Wasabi
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Not all ductile alloys neck. See, for example, Haynes 25 (L605).

Don
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