|The ASTM E1820 specification has
been developed to provide a common method for determining all applicable toughness parameters from a single test. Other specifications include E813,
E1152, and E1737.
The J parameter is a measure of energy needed to drive
a crack under monotonic loading conditions. This value is calculated at
several points along a loading curve. The load line compliance and the area
under the load vs. clip gage opening displacement curve are used in
calculating the crack length and J values. A plot of J versus the change in
crack length is then plotted. A least squares curve is then plotted through
the valid data set. Where this regression line crosses an offset line, a
qualification J is chosen and called Jq. A series of validity checks are
then run. If these checks pass, the qualification J is then termed JIC.
ASTM E1152, is designed to determine a
resistance curve. This test requires the sample crack growth to be extended
farther than an E813 test. Like E813, this test plots the change in crack
length versus the J parameter, but unlike E813, this test makes no claims to
give an exact number to the material. Instead it is used to generate a
function which relates the J value to the change in crack length, i.e.: J = f(Da).