Dynamic K_c Testing of Structural Steel

Fracture toughness K_c values were determined for structural steels in thickness and at loading rates and temperatures representative of service conditions for many civil structures, with particular interest centered on bridges. The measurements were made using notched-bend tests with specimens 3-in. deep, 12-in. long, the full plate thickness, and with notches fatigue precracked to a depth of 1 in. The K_c values were computed using the observed maximum load and a crack size plasticity adjustment. A cushioned drop-weight loading technique provided loading times of 0.5 x 10^-³ sec to 2 x 10^-³ sec. Strain gages on the loading tup of the free-falling weight permitted load-time recordings for the tests. The limitation on useful K_c determinations due to specimen size was approximately 1.25 (in.)^1,2 in. times the applicable yield strength of the steel. The test results presented are for temperatures ranging from –120° to 60°F and include, for comparison, results obtained with loading times of 1 – 3 sec.