I hope some of you may find this work interesting.

Fracture toughness characterization through notched small punch test specimens

http://www.sciencedirect.com/science/article/pii/S0921509316300740

(A preprint version is available at www.empaneda.com)

In this work a novel methodology for fracture toughness characterization by means of the small punch test (SPT) is presented. Notched specimens are employed and fracture resistance is assessed through a critical value of the notch mouth displacement Xspt. Finite element simulations and interrupted experiments are used to track the evolution of Dspt as a function of the punch displacement. The onset of crack propagation is identified by means of a ductile damage model and the outcome is compared to the crack tip opening displacement estimated from conventional tests at crack initiation. The proposed numerical-experimental scheme is examined with two different grades of CrMoV steel and the differences in material toughness captured. Limitations and uncertainties arising from the different damage phenomena observed in the lowest toughness material examined are thoroughly discussed.

I am working on the validation of CTOD.

In the evaluation of CTOD using the
J-integral approach as applied in ASTM E1290 and E1820, the plastic J
component is defined as (Npl*Apl)/(Bn*Bo)
Npl=dimensionless constant(plasticity)
Apl=area under load vs. displacement plot
Bn=ligamen length (W-a)
Bo=section thickness

On E1820 there are different functions provided for Npl if Apl is
evaluated differently (CMOD or load-line displacement).

Do anybody know what are the relation of the Npl to Apl and how they interact
for the J-integral evaluation?