Elastic-plastic Fracture Toughness in Nodular Cast Iron

Abstract

In the nodular cast iron and the compacted vermicular cast iron with a ferrite matrix, the elasticplastic fracture toughness J_IC was evaluated by means of acoustic emission, electric potential and Rcurve method based on ASTM E 813. J_in (AE) and J_in (EP), estimated from rapid increasing points in cumulative number of AE events and electric potential difference respectively, correspond with a small amount of crack extension in the mid-thickness of specimen. J_in (R), on the other hand, estimated from R-curve method, corresponds with an appropriate amount of crack extension which is nearly equal to 2δ_c. In the present analysis, J_IC was optimized from J_in (R).
Dependence of J_IC on graphite nodularity n was represented by
J_IC=62-14.7 (n^-1/2-n^3/2) (kJ/m²)
using the critical condition of void coalescence that R=X where R is a mean radius of voids developed around graphite nodules and X is an inter-nodule spacing, respectively.