THE EFFECT OF CRACK SHAPE ON FRACTURE TOUGHNESS.
DOUGLAS AIRCRAFT CO INC SANTA MONICA CALIF
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An investigation was made to determine the effect of crack eccentricity upon fracture toughness. Fracture toughness tests, using partial thickness crack PTC coupons, were performed on two heats and three thick nesses of the l8Ni-9Co-5Mo 300 psi maraging steel. In addition, data on tempered 4340 steel and aged Ti-6Al6V-2Sn were taken from the literature and analyzed. The results to date indicate l. Crack ellipticity need not be considered if the gross fracture strength is represented as a function of crack length. However, crack eccentricity must be considered if gross fracture strength is represented as a function of crack depth or crack area. 2. Irwins constant, as defined by Irwins equation, is not a constant when eccentricity is varied, and should not be used to judge fracture toughness unless the eccentricity of the cracks has been kept constant. 3. A new parameter, C, similar to Irwins constant, is introduced. This, unlike Irwins constant, is apparently unaffected by crack eccentricity. It is suggested that this new parameter might have a wider application than Irwins constant. Author