Observations on Use of the J Integral to Determine Plane-Strain Fracture Toughness from Subsized Specimens of a Titanium 6Al-4V Alloy
NAVAL RESEARCH LAB WASHINGTON DC WASHINGTON
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J-integral procedures were used to obtain resistance curves of J versus crack extension from fatigue-precracked specimens of a titanium 6Al-4V alloy. Specimens of various geometries were employed, all in three-point bending. Crack extensions were delineated by heat tinting. The value of the J integral at the initiation of crack extension, J sub Ic, was determined from the resistance curves and compared with a valid K sub Ic value for this material. Comparison was made of the results obtained with the approximation equation J 2ABb to those obtained with the more cumbersome compliance technique in which the analytical plane-stress solutions of Bucci et al. were used. The range of ratios of crack length to specimen width was examined over which J 2ABb holds, as was the decrease in crack extension at the experimental limit load with increase in ratio of specimen thickness to uncracked ligament. Variation in J sub Ic from specimens cut from different positions through the plate thickness was also explored.