Application of the ac potential drop technique to the determination of R curves of tough ferritic steels

✍ Scribed by N. Okumura; T.V. Venkatasubramanian; B.A. Unvala; T.J. Baker

• Publisher: Elsevier Science
• Year: 1981
• Tongue: English
• Weight: 710 KB
• Volume: 14
• Category: Article
• ISSN: 0013-7944
• DOI: 10.1016/0013-7944(81)90048-5

✦ Synopsis

The suitability of the AC potential drop (ACPD) technique for detecting crack initiation and monitoring crack extension during slow stable growth has been investigated using side-grooved Charpy size specimens tested in three point bending. For ferritic steels with widely differing initiation and growth characteristics, the potential drop (PD) vs clip gauge opening displacement (CGOD) trace shows consistent behaviour, the most important feature being the occurrence of a minimum around the point of crack initiation. At low current frequency (150 Hz), there is close agreement between &in, the COD corresponding to the minimum of the PD/CGOD trace and 3 estimated by the recommended multispecimen technique for ai ranging from 0.02 to 0.37 mm. In steels with Si less than about 0.1 mm, the minimum occurs at the same value of 8 for both low (150 Hz) and high (4.7 kHz) frequencies. However, for steels with higher toughness, the minimum shifts to lower 6 values as the frequency is increased. It appears that for any steel, there is a maximum frequency below which the minimum corresponds to Si. It is demonstrated that the ACPD method can be employed to determine R curves from single specimens.