On the unloading compliance method for crack length measurement

Unloading compliance tests have been performed on blunt notched Charpy specimens in order to quantify the extraneous displacements arising during unloading in a three point bend fracture toughness testing fixture. An expression is derived which quantifies the extraneous displacements and enables the unloading compliance to be accurately evaluated. Results are presented from tests on pre-cracked Charpy specimens which demonstrate close agreement between measured crack lengths and those predicted using the corrected unloading compliance.