Chevron-notched toughness of materials with rising fracture resistance curves

The effect of rising resistance curves on the fracture tougness determined from chevron-notched beam tests is estimated via a set of simple numerical calculations, It is shown that for materials with a rising resistance curve, the toughnesses determined by the peak load method and by the work of fracture method are both higher than the initiation toughness, and both depend on the sample size relative to the length over which the resistance curve increases. It is also found that the toughness based on the work of fracture is higher than that based on the peak load, Fracture toughness data obtained from tests of a nickel-alumina composite are discussed in light of the results of the numerical calculation.