Distribution of Microdefects in Sheets of St1.03-12 Low-Carbon Steel in Tension at Different Rates
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DISTRIBUTION OF MICRODEFECTS IN SHEETS OF ST1.03-12 LOW-CARBON STEEL IN TENSION AT DIFFERENT RATES O. R. Hokhman,1 N. A. Volchok,1, 2 and D. Fassmann3
UDC 669.295 : 669.76 : 621.982.45
We study the influence of the tensile strain rate on the anisotropy of Young’s modulus, the yield strength, and damage coefficient of sheets of St1.03 12 low-carbon steel (0.06% С, to 0.35 Mn, to 0.40 Si, and ∼ 0.025% S and P). It was established that, with increase in the strain rate from 0.0017 up to 5 mm/sec, texture transformations occur, Young’s modulus decreases, and, with decrease in the anisotropy of damages of the sheets, the yield strength and damage coefficient increase. Keywords: tension, loading rate, Young’s modulus, yield strength, anisotropy, texture, damage coefficient.
The hidden fracture of a body is accompanied by the formation and development of a scattered field of microdefects (microcracks under elastic deformation, dislocations under plastic deformation, micropores in creep, ! ! and surface microcracks in fatigue) [1]. In this case, the effective area of an element dS * (n) ( n is a normal to
the plane dS * ) of an imaginary section of the body that transfers the load from one of its parts to another due to ! the distribution of microdefects in the body, is smaller than the area of the same element dS(n) in the case where the character of defects is neglected. The ratio of these areas
! dS * (n) ! D(n) = ! dS(n) is called the damage coefficient. Strictly speaking, the value of D must be computed according to results of fractographic investigations. However, these investigations are laborious and, for this reason, it is customary to use indirect methods of calculation according to the changes in the physical and mechanical properties, Young’s modulus, electric resistivity, yield strength, etc. [2, 3]. The damage coefficient is determined most accurately for given Young’s moduli of the material in the damaged (E D ) and intact (E0 ) states [3]. However, since Young’s modulus is the quantity inverse to the component of the compliance tensor s1111 [4], which depends on the direction of measurements in textured objects, it is possible to expect, in the analyzed case, the anisotropy of the coefficient D , especially for sheet materials [5].
The aim of our investigations is to study the influence of tensile strain rate on the coefficient D in the principal directions of the sheets of St1.03-12 steel (0.06% С, ≤ 0.35% Mn, ≤ 0.40% Si, and ∼ 0.025% S and P; its Ukrainian analog is 08 steel). 1 2 3
Ushyns’kyi South-Ukrainian National Pedagogical University, Odessa, Ukraine. e-mail: [email protected] (corresponding author).
Institut für Werkstoffkunde, Leibniz Universität Hannover, Garbsen, Germany.
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 49, No. 2, pp. 59–64, March–April, 2013. Original article submitted December 7, 2012. 1068-820X/13/4902–0199
© 2013
Springer Science+Business Media New York
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D. FASSMANN
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