Some aspects of the deformation of cast iron under tensile loading
Static and repeated tensile tests have been carried out on a flake graphite and spheroidal graphite cast iron, to follow the development of longitudinal permanent strains. Permanent strains have been found to develop at ambient temperature for both loading conditions at stress levels below the 0.05% and 0.005% proof stress values, for the flake graphite and spheroidal graphite iron respectively.
In addition, certain differences in the development of permanent strains for the two irons with cyclic and static loading have been demonstrated.
Examination has been made of the phenomenon known as 'Limit of Accommodation' (σL), defined as the maximum stress whose repeated application should lead to the permanent strains reaching a limiting value after a certain number of load applications, the permanent strain thereafter remaining unchanged with further applications of stress. Values for σL have been quoted for the irons, whilst difficulties associated with its determination, together with its relevance to the mechanical characteristics of cast iron have been discussed.
Based on the assumption that graphite may be regarded as a cavity, an hypothesis is proposed to account for the behaviour observed during repeated loading and to explain the shape of the loading and unloading curves for flake graphite iron.
Finally, by simulating the defects present in cast iron using a simple perforated steel sheet model, an attempt has been made to verify experimentally the proposed mechanism of deformation occurring during the tensile loading of cast iron.
- Mechanical, Electrical and Manufacturing Engineering