Abstract
The objective of this study is to characterize the behavior of dynamic fracture toughness of a thick-walled ferritic spheroidal graphite iron and to evaluate this material for unstable fracture.
Unlike static elastic-plastic fracture toughness JIc, the distribution of graphite nodule has a very slight effect on the upper shelf dynamic elastic-plastic fracture toughness JId. Upper shelf fracture toughness increases with increase in stress intensity rate K. This increase in fracture toughness is mainly attributed to increase in strength at high rate of K.
Ductile-brittle transition temperature is linearly related to the logarithm of K. In the upper shelf region, converted plane strain fracture toughness divided by yield strength can be adopted as a material constant that is independent of K and temperature. On the basis of the JIC-temperature curve and the results of impact bending tests on small size specimens, it can be made to estimate the behavior of JId as for temperature and the predetermined K.
In the upper shelf region of the material investigated, the maximum allowable surface flaw depth exceeds the minimum detectable flaw size by a nondestructive inspection. Ferritic spheroidal graphite iron can be used as a material for casks in the upper shelf region at least.
