Fracture Strain (Shear Damage)

[Vxxxxx]

Hi, I am using Shear Damage and I would like to know which strain is Fracture Strain defined in ABAQUS.

Red or Blue?

Thank you.

 

[RBureau]

Hi,

From what I gather, if you use *SHEAR FAILURE, the fracture strain is the red one.

Regards

 

[FEA way]

I assume that you are talking about the shear damage initation criterion (*Damage initation, criterion=shear). Generally, damage initiation criteria (like this one) always describe the onset of damage - point with damage variable D=0 marked in red. Also, in the documentation for *Damage Initiation keyword you can find information that in case of criterion=shear you have to specify equivalent plastic strain at damage initiation (fracture strain), shear stress ratio and strain rate.

There’s also a shear failure model (*Shear failure) but it’s a different feature, doesn’t belong to progressive damage and failure models described with this curve that you attached, can be used only in Explicit and is neither available in CAE nor recommended to use.

 

[Vxxxxx]

Thank you very much, RBureau and FEA way.

Noted. So for the first example(black curve), if the stress dropped twice, I still refer to the first drop(red arrow) as the onset of damage right?

As for the second example (683K), the curve rise and drop, then rise again before dropping back to 0. So should I take orange arrow or green arrow as onset of damage?

 

[FEA way]

Well, the model for progressive damage and failure used in Abaqus is simpler - it uses single point for damage initiation and then assumes the evolution of damage (according to damage evolution law) up to failure. So you have to make some assumptions and simplify your data to match the model available in Abaqus.

 

[RBureau]

As FEA Way mentioned, the couple of keywords *DAMAGE INITIATION and *DAMAGE EVOLUTION are used to define progressive damage. Subsequently, it is adapted to ductile materials. In your first example, I would still refer to the first drop as the onset of damage. However, given that you have a fragile type of failure, I would question the validity of the "progressive damage" framework.

In your second example, the orange arrow corresponds more of less to the elastic limit in my opinion. I'd take the green one as the onset of damage. Be aware though, that you have to use the plastic strain, not the total strain, when using the keyword *DAMAGE INITIATION with the ductile or Johnson-Cook criterion.

 

[Vxxxxx]

Noted. Thank you RBureau and FEA way. Both your answers have been of great help. Thank you.