Jq from ASTM E1820, Relation to Assumed Elastic Modulus 1

[mcclain]

Jq from ASTM 1820, Relation to Elastic Modulus

I have a set of fracture toughness test data from a vendor.
The initial submittal used an inappropriate (too high) elastic modulus.
The data was resubmitted after being evaluated using a lower modulus.

Both Jq and Kjq decreased with the lower assumed modulus. I can see why Kjq would decrease with decreasing elastic modulus. But why would Jq decrease? Annex 9 of ASTM E1820 was used.

Thanks,
Mark

 

[CoryPad]

J_Q uses the J vs. [Δ]a data. The J data is a function of K (see, for example, equations A1.5, A2.5 & A3.5). Since K is a function of E, J also is a function of E.

Regards,

Cory

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

 

[mcclain]

Thanks Cory.

Is there a simple way to estimate a new J for a different modulus assumption?

 

[CoryPad]

Only the elastic J portion (J_el) changes with elastic modulus. The plastic portion usually is much higher, but that is only after plasticity initiation. There is an inverse relationship between J and E, so the change can be substantial.

For example, if you originally had data calculated with E = 210 GPa (modulus for ferritic steel), but it really was E = 200 GPa (modulus for austenitic steel, a 5% difference), then J_el will vary by about 5%.

But, if you originally used E = 200 GPa (steel), but the material is aluminum with E = 70 GPa, then the J_el difference is 65%.

Regards,

Cory

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