SYMPOSIA PAPER Published: 01 January 1997

Influence of Pre-strain on Fracture Toughness and Stable Crack Growth in Low Carbon Steels


Experimental investigations demonstrate a significant effect of pre-strain on fracture toughness and stable crack growth resistance of a low carbon structural steel. Fracture toughness, Ji for the onset of stable ductile crack growth is decreased to one half with a 9% pre-strain due to cold rolling. The characteristic distance model for ductile crack initiation was applied to analyze parameters affecting the degradation of fracture resistance. The model predicts that value of Ji is given as a linear function of yield strength and ductility of the material. In order to confirm the theoretical prediction, notched round bar tensile tests were performed and ductility under a high triaxial stress state was measured. Critical plastic strain for micro-void coalescence is significantly decreased with increasing pre-strain. Degradation in Ji due to pre-strain can be well explained by the characteristic distance model.

To clarify micro-mechanisms of degradation in ductility due to pre-strain, fracture process in notched round bar specimens was investigated emphasizing the role of micro-void nucleation and growth. Experimental observation indicates that the significant decrease of the critical strain due to pre-strain is attributed to the increase of void nucleation sites under a high triaxial stress state.

Author Information

Miyata, T
Nagoya University, Japan
Tagawa, T
Nagoya University, Japan
Aihara, S
Nagoya Research Laboratories, Nippon Steel Corp., Japan
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Developed by Committee: E08
Pages: 167–176
DOI: 10.1520/STP12307S
ISBN-EB: 978-0-8031-5374-5
ISBN-13: 978-0-8031-2410-3