Initial,post limit,secant stiffness

[Sadeq]

Hello,

My question is simple, but it does confuse me.

I need to know the exact difference between
Initial stiffness,post limit stiffness, and secant stiffness in details please

Please clarify this on graph if possible

Thank you

 

[SteamKing]

What have you looked up about these topics so far?

 

[Sadeq]

I know that initial stiffness is the tangential stiffness at the beginning and the secant stiffness represent, the secant line passing through 0,0 and the final point( yield point).But still confuse about the post limit stiffness, that way i asked for drawing to clarify them all at the same graph

Thank you

 

[pongo38]

What limit is it that you think it refers to?

 

[Sadeq]

I don't know exactly that's why i am asking if anyone know about post stiffness concept.
Thank you

 

[Sadeq]

http://postimg.org/image/3n5smqb35/

in this picture a book mention that the post-limit stiffness of the component (upon yielding) is notably reduced in the case of the higher bolt grade(red line).

And i don't understand post stiffness.

Help me please

 

[PhanthomJay]

What is the significance of the slope of the stress strain curve before and after yield?