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Jq from ASTM E1820, Relation to Assumed Elastic Modulus

thread177-189441

Jq from ASTM E1820, Relation to Assumed Elastic Modulus

Jq from ASTM E1820, Relation to Assumed Elastic Modulus

(OP)
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

RE: Jq from ASTM E1820, Relation to Assumed Elastic Modulus

JQ uses the J vs. Δa 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

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RE: Jq from ASTM E1820, Relation to Assumed Elastic Modulus

(OP)
Thanks Cory.

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

RE: Jq from ASTM E1820, Relation to Assumed Elastic Modulus

Only the elastic J portion (Jel) 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 Jel 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 Jel difference is 65%.

Regards,

Cory

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