Volume 22, Issue 6 (November 1994)
Inconsistencies between CTOD and J Calculations
Crack-tip opening displacement (CTOD) determined using the plastic hinge model included in the ASTM E 1290 (Test Method for Crack-Tip Opening Displacement (CTOD) Fracture Toughness Measurement) is inconsistent with CTOD determined using the ASTM E 813 (Test Method for JIc. Measure of Fracture Toughness) combined with an equation relating J to CTOD. The plastic hinge model is also inconsistent with the EPRI handbook estimation scheme. The plastic hinge model is highly inaccurate for hardening materials. To explore these inconsistencies, the EPRI scheme was used to generate theoretical load-displacement curves of a compact tension (CT) specimen for a wide range of materials and crack sizes. An alternate equation, derived for a power law hardening material, is shown to be consistent with both the ASTM E 813 and the EPRI handbook estimation scheme. The alternate equation accounts for nonlinearities in the relationship between CTOD and plastic load-line displacements. Differences between the alternate equation and the EPRI scheme are discussed. Experimental results demonstrate the inaccuracy of the plastic hinge model and the accuracy of the power law model.