I am calculating eta factor for 17 wide mm flat CT, axial curved CT and transverse curved CT specimens for fracture toughness testing of Indian Zr-2.5Nb pressure tube material experimentally (using energy release and load separation method as described by Landes) as well as numerically using limit load method. I want to know the minimum and maximum limit of a/W between which energy release and limit load can be calculated to fit energy release and limit load with a/W. I also want to know reason for minimum and maximum limit of a/W.
Check the text and relevant cited references for the pages 15-17 of X.-K. Zhu, J.A. Joyce / Engineering Fracture Mechanics 85 (2012) 1–46, where the matter has been discussed.
You can look at my paper published in Key Engineering Materials, 2007, Vols. 345-346, pp. 449-452.
To apply the concepts of linear elastic fracture mechanics with the use of its stress intensity factor to characterize the crack tip stress field, small scale yielding condition should be met. The ratio of the plastic zone radius, rp, and the crack length, a, should be less than 0.02. This means that
rp = K2 / 6(pi)((yield stress)2 in the plane strain state < 0.02
rp = K2 / 2(pi)((yield stress)2 in the plane stress state < 0.02
K2 = Y2 (applied stress)2 (pi) a
Y is the geometrical factor in the mathematical form of the SIF and is a function of a/W dependent on the type of loading and crack geometry.
Thus, you may plot Y2 against a/W. If Y2 < C then ealstic energy release rates may be invoked.
C = ( 2 - 6 ) 0.02/pi (yield stress/applied stress)2
i
Dear Dr. Hammouda,
Thank you very much for your reply.
eta factor is applicable for elastic plastic fracture mechanics whereas K is applicable for elastic fracture mechanics. I want to know the range of a/W between which I should fit limit load and energy release rate to a/W to calculate eta factor.
Dear Dr. Matvienko,
Thank you very much for your reply.
In your paper you refer in the answer, eta factor for 17 mm curved CT specimen of Zr-2.5Nb pressure was calculated using load separation method is calculated between a/W of 0.5 to 0.6. there is no mentioned of lower and upper limit of a/W for calculating eta.
This might give you an answer https://www.researchgate.net/publication/226274314_Review_and_Extension_of_Compliance_Information_for_Common_Crack_Growth_Specimens
Article Review and Extension of Compliance Information for Common Cr...
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