NDTnet 1998 Aug, Vol.3 No.8

Abstract

In present paper a relation between yield stress and parameters, obtained by static and dynamic indentation is discussed. Low carbon steels were tested, and parameter with correlation was chosen.

Four steels, used in pipelines, were subjected by step loading and by impact loading with rigid indenter from tungsten carbon with a spherical active tip. Static loading was performed with a Vickers hardness meter. Measured curve P= P(d) was fitted by Mayer's law P = a* dⁿ by least square method, and a dependence of loading force P upon residual plastic displacement in impression _p was computed using a model of interaction of rigid sphere with elastic - plastic halfspace (1). Impact loading gave a continuous curve P= P(), which was recalculated in P = P(d) and P = P(_p) by the same model.

A dependence of stress intensity upon plastic strain was obtained with tensile machine INSTRON, using extensometer. The value of stress, corresponding to strain of 0.002 was calculated, extrapolating the curve = () by Ludwik - Hollomon's fit = A* ⁿ for material with Luder's elongation.

It is explained as follows: 1) deformation while Luder's elongation and after it consists in different physical processes, which are rather independent (2); 2) while indentation we deal with strain above 0.025, which is over than 0.015 at the end of Luder's elongahon.

Stress at 0.002 was compared with parameter a in Mayer's law, Brinell and Mayer's hardness and plastic hardness obtained from both dynamic and static indentations. Plastic hardness was calculated as

where D is a diameter of curvature of indentertip. It was a constant value when strain has ranged from 0.02 to 0.07. The plastic hardness was found to correlate with yield stress in a best manner.

1. V.A. Rudnitsky, V.V. Djakovich. Material testing by the method of dynamic indentation. Nondestr. Test. Eval., 1996, Vol. 12, pp. 253-261
2. Werkstoffkunde Eisen und Stahl, Herausgegeben von Professor Dr. Rer. Nat. Winfried Dahl, Aachen Dipl.-Ing. Winfried Anton. 1983, Verlag Stahleisen mbH, Düsseldorf.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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