Published: Jan 1988
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In a test program motivated by the need for a quantitative relationship between fracture toughness, flaw size, and applied loading for small flaws, to be used for fitness-for-service assessment, applied J-integral was measured as a function of applied strain in eight 14-mm-thick specimens of ASTM A710 Grade A Class 3 steel plate. All the edge cracks had lengths less than 3% of the specimen width of 82 mm. Six specimens were tested in tension; two were loaded by four-point-bending in the plane of the plate. One single-edge-cracked, transversely oriented specimen was tested at −30°C. Electrical resistance strain gage and clip-gage crack mouth opening displacement measurements were used to obtain quantities inside the J-integral. The J-integral was calculated by trapezoidal rule integration. Unloading crack mouth compliance measurements were used to obtain crack length values so that tearing effects could be observed.
Lüders strains occurring right after yield caused rapid increases in the applied J-integral values for the tension specimens. Except for the Lüders strain effect, the behavior of the applied J-integral in bending was similar to that in tension. Tearing caused a smooth exponential rise in applied J as strain increased beyond the point of initiation. The initiation toughness and tearing resistance of the panels with short cracks were equal to or greater than those of conventional three-point-bend specimens of the same thickness. No effect of temperature on applied J-integral was found from the specimen tested at −30°C. The present data support Wilson's prediction of the dependence of J on strain for a material with a bilinear stress-strain curve.
bending, fracture, J-integral, J-R curve, single-edge crack, surface crack, tension, toughness
Physicist, National Bureau of Standards, Boulder, CO