Kc value in RAPID material database

[Ruag]

Hi,
back to RAPID again.
Does anybody know the origin of the Kc=153 ksi sqr(in) tabulated in the material database of 2024-T3?
It should have something to do with the apparent fracture toughness. I can't find any clarification in the letterature.
Thanks!

 

[rb1957]

i'm guessing that it's derived from your inputs ... 0.008" thk is pretty thin

 

[YoungTurk]

MMPDS has tables of fracture toughness for aluminum in chapter 3. It does not contain values for 2024-T3 (likely because fracture is not typically a failure mode for thin sheet), but the max values for K1c (first mode fracture, crack opening) for any alumimum alloy listed do not exceed 50 ksi root inches.

What are you trying to evaluate with this value?

Also - this is effectively a double post, please refrain from double posting per the forum policy.

 

[rb1957]

K1c is plain strain fracture toughness, applicable to thick sections.
Kc is plane stress fracture toughness, applicable for thin sheet. in my experience 153 ksi.in^1/2 is quite reasonable.

 

[Ruag]

I am estonished as well about this high value. Unfortunately I have not found anything in the leterature that can clarify it.
For 2024 T3 clad sheed Kc is not an user input, but it is part of the material database.
RAPID manual says that if Kc is not present, then it will be automatically calculated using the NASGRO equation Kc/KIc=1+Bk*e^-(Ak*t/t0)^2 where t0= 2.5(KIc/Fty)^2.

Using Ak and Bk =1 as per NASGRO's material table I get Kc=66 Ksi sqr(in) for a t=0.05 in.

Dear rb1957: can you substantiate you assessment with more details, please?

Dear YoungTurk: this value is taking a part in the crack growth & residual strength calculation in the RAPID software.

Thanks to all

 

[rb1957]

test data from an OEM, i've seen 200 ksi.in1/2 for 0.06" thick 2024T3