From a group of 96 specimens ranging in thickness from 15 to 38 mm (0.60 to 1.50 in.), a regression equation was obtained for Ti-6A1-4V plate relating the fracture toughness, K_Q, of 205-mm (8-in.) wide specimens to the variables of specimen thickness and fracture toughness, K_Q, for 76-mm (3-in.) width. The fracture toughness value of Ti-6A1-4V plate can be increased appreciably in thin specimens by using an oversized width specimen. The magnitude of this toughness increase diminishes as the thickness increases and approaches 38-mm (1.5-in.). Oversizing the specimen results in a significant reduction in the stress at instability at 2 percent crack extension. The specimen strength ratio, R_sc, essentially remains the same while K_max and the P_max/P_Q ratio increase.

Crack-growth-resistance curves constructed from load versus crack-opening-displacement curves for the two different width specimens are similar. This indicates the fracture behavior is the same and not altered with increased specimen width. Furthermore, K values for oversized specimens can be calculated from the loads at the appropriate crack extension in smaller standard size specimens, and vice versa.