Construction of an extended hardening curve by compression of composite cylindrical specimens

Abstract

TA technique for construction of an experimental hardening curve based on the experience of compression of cylindrical specimens made of 11YuA steel is presented. The upsetting of specimens with 9 mm high and 5 mm in diameter was carried out on a R-5 testing machine with the recording of the “load-displacement” diagram. To reduce the influence of friction forces between the upset workpiece and the tool, the experiment was completed when the ratio of height to its diameter was equal to 1. This leads to a limitation of the range of the resulting strain intensity within 0.35 ... 0.45. To expand the boundaries of constructing the hardening curve, two composite samples obtained after the first upset were deformed, which made it possible to achieve a strain intensity of 0.75 ... 0.85 in each sample. Since the sample was compressed with the constant rate, the “load-displacement” graph was divided into several intervals, in which, in accordance with the displacement of the pressure plate, the cross-sectional area of the sample, deformation, load, and the corresponding stresses were determined. The set of obtained values of strain and stress intensities made it possible to plot the hardening curve of the studied material with subsequent approximation by a linear function. Hardening curves show that the nature of hardening of the material under study does not change as a result of a compressive test of a composite sample, therefore, contact friction forces do not affect the power parameters at significant strain rates. The proposed compression test method using a composite sample can significantly reduce the complexity of constructing a hardening curve and significantly expand the range of uniform deformation under uniaxial stress conditions.The work was carried out within the framework of the RFBR grant No. 20-08-00401 A.