The Significance of Maximum Load on a Load-Displacement Curve with Stable Crack Extension

The ASTM standard method for the measurement of fracture toughness, E 1820 [

1

], covers procedures and guidelines for the determination of this material property in metallic materials using the parameters

K, J

or

CTOD

. The fracture toughness may be measured as a point value, or as a complete fracture toughness resistance curve. In the latter option a

J

- or

CTOD

-based resistance curve may be obtained from a single specimen fracture test, in which the crack length is measured from compliance changes, and later verified by optical measurements. The single specimen

J-R

curve construction procedure defined in E1820 involves several steps, which go from obtaining and plotting the raw

J-Δa

data, to calculating an interim value of

J

, termed

J

Q

, to finally qualifying

J

Q

as

J

Ic

, a size-independent value of fracture toughness.