A computer interactive unloading compliance single-specimen J_Ic test procedure has been developed. This procedure utilizes an on-line minicomputer to analyze digitized load-displacement data during testing. Unique values of J_I and crack length are determined from compliance measurement on short unloadings along the load displacement record. The test procedure is presented in detail and analysis procedures are discussed.

Three tasks which demonstrate the validity and utility of the computer interactive test method are discussed. Results for single-specimen and multiple-specimen tests are presented for HY 130, 10Ni steel, 17-4PH steel, Ti-7Al-2Cb-1Ta, and Ti-6Al-4V which show close correspondence between the two methods. Tests on 17-4PH steel compact tension specimens with various thicknesses and crack lengths are summarized and dimensional effects on J_Ic and the J-Δa resistance curve slopes are discussed. Finally, tests on HY 130 specimens with various notch root radii demonstrate effects of notch acuity on J_Ic.