Relationship between dynamic and static toughness of flake and compacted graphite cast irons

The very little plastic deformation exhibited in the fracturing of flake gr aphite (FG) and compacted graphite (CG) cast irons qualified them as brittl e materials. The fatigue pre-cracking of these brittle material in K-1C pla ne strain fracture toughness testing is a difficult task. Opposed to this s tatic toughness K-1C, the dynamic toughness obtained by impact testing does not have such problems. Since the stress-strain behavior of brittle materi al is essentially linear and the fracture appearance of the specimens after impact testing must largely be flat without shear-lip, these conditions al so satisfy the linear-elastic requirement in K-1C testing. Thus, it is of i nterest to find out if there's any linear relationship existed between thes e two toughness properties of brittle material. Annealing, normalizing, and austempering heat treatment were applied to FG and CG irons to alter their matrix structures so as to obtain a range of static (K-1C) and dynamic (im pact) toughness values. A third toughness, calculated by integrating the ar ea under the load versus CGD (Clip Gage Displacement) curve in K-1C testing , was termed 'calculated toughness' and was also listed for comparison purp oses. It was found, among dynamic impact toughness (X), static K-1C (Y), an d calculated toughness (Z), linear relationships exist for flake graphite c ast iron as: Y = 4.02X - 0.81 Z = 1.75X + 2.99 and for compacted graphite c ast iron as: Y = 0.86X + 20.2 Z = 0.77X + 4.77. (C) 2000 Elsevier Science S .A. All rights reserved.