A precise experimental method to determine X-calibration factors from compliance measurements is presented. The usefulness of the method is demonstrated on a series of single edge-notch bend specimens loaded in four-point bending with relative notch depths ranging from 0.15 to 0.91.
The results are expressed in terms of a convenient dimensionless parameter Z(X) = c&N(X) -NO)/NO), where N(X) and N, are the compliance of the notched and the umrotched specimens respectively, and co is a constant depending only on test and specimen geometry. Comparision of the measured data with published results calculated by boundary collocation procedures shows an excellent agreement.
Investigations of specimen compliance as a function of the notch width indicate that the effect of using a machined slot to simulate an atomically sharp crack is negligibly small up to 0.25 mm notch width. NOTATION specimen thickness notch depth or crack length Young's modulus upper span length (critical) strain energy release rate specimen height (critical) stress intensity factor lower span length compliance of the unnotched sample compliance of the unnotched sample loaded on its narrow face compliance of the unnotched sample loaded on its broad face compliance of the notched sample applied load deflection of the unnotched sample deflection of the notched sample deformation of the bending apparatus notch width relative notch or crack length K calibration factor relative compliance increase Poisson's ratio notch root radius nominal applied stress
The -on the symbols N and s designates "as-measured".