Elastic-Plastic Fracture Toughness (JIC) Testing
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).