Plastic deformation beyond the ultimate strength

Gulyaev, A. P.

doi:10.1007/bf01154081

Met Sci Heat Treat

1996

DOI: 10.1007/bf01154081

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Plastic deformation beyond the ultimate strength

A. P. Gulyaev¹

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1997

1998

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Cited by 2 publications

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“…It is also possib!e that hydrogen will react with free carbon present in the structure in the form of an interstitial solid solution or graphite in accordance with reaction (2).…”

mentioning

confidence: 94%

“…Figure 1 presents a comparatively even decrease in the density p of the material over the length of a specimen after a tensile test (by 0.01-0.36% in regions [2][3][4][5][6][7][8] and a jumpwise decrease by a factor of 4.8 -132 (by 1.72%) in the Ukhta Industrial Institute, Ukhta, Russia. fracture zone 9 [2], which is explained by an increase in the porosity of the material.…”

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confidence: 99%

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Behavior of hydrogen in fracture and friction of metals and alloys

Suranov

1998

Met Sci Heat Treat

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The negative effect of hydrogen on the properties of metals and alloys is demonstrated by the results of many studies. However, the mechanism of the behavior of hydrogen in metals still remains unclear. The present work is devoted to the effect of magnetic and electric fields on the diffusion of active hydrogen and to its interaction with impurity elements in metals and alloys in fracture and friction.An increase in the hydrogen content in metals and alloys often leads to substantial worsening of their physical, mechanical, and triboengineering properties and, consequently, to brittle fracture and intense wear of parts even under a meager load. Friction is accompanied by anomalous phenomena, namely, the wear of a steel (or cast iron) part with an elevated hydrogen content turns out to be higher than that of a less hard bronze (or plastic) part operating together with it [1].The harmful effect of hydrogen manifests itself quite vividly in electrolytic hydrogen-charging of a bent steel plate made of a tool steel (Kh6VF) or a corrosion-resistant steel that undergoes brittle fracture (sometimes into three parts) several minutes after the process begins, depending on the degree of deformation. At room temperature such a plate can be in a deformed state for several months and even years without breaking. A deformed steel plate breaks rapidly by a brittle mechanism after its stretched surface is wetted by an electrolyte without passing an electric current.Since the degree of deformation e and the load P acting on the specimen before and after the surface is wetted by an electrolyte (before and after hydrogen absorption) are constant, the development of brittle fracture is obviously caused by an increase in the stresses cr in the specimen to values exceeding the ultimate rupture strength of the material er r due to a reduction in the cross-sectional area of the specimen F, i.e., (or = P/F) > c~ r . Figure 1 presents a comparatively even decrease in the density p of the material over the length of a specimen after a tensile test (by 0.01-0.36% in regions [2][3][4][5][6][7][8] and a jumpwise decrease by a factor of 4.8 -132 (by 1.72%) in the Ukhta Industrial Institute, Ukhta, Russia. fracture zone 9 [2], which is explained by an increase in the porosity of the material.The appearance of pores 0.2 -1.0 I-tm in diameter and even of tube channels 2 to 10-50 lam long, which sometimes merge, forming a scaling system in the surface layer 2 -8 pan deep, has been observed in friction tests of specimens of corrosion-resistant steel 07Khl6N6 [3]. In parts made of steel 45, after operation under wear conditions pores up to 10 pan in diameter and several tens of micrometers long form chains that reach the surface without signs of crack propagation, although in the initial state the material does not have noticeable pores. The marked decrease in the density of the metal in the fracture zone, the changes in the specific elongation and reduction of area, and the proportions of brittle and tough fracture on the surface of specimens, just ...

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“…It is also possib!e that hydrogen will react with free carbon present in the structure in the form of an interstitial solid solution or graphite in accordance with reaction (2).…”

mentioning

confidence: 94%

mentioning

confidence: 99%

Behavior of hydrogen in fracture and friction of metals and alloys

Suranov

1998

Met Sci Heat Treat

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“…The need to determine this characteristic has been demonstrated by A. P. Gulyaev in [10]. The stress at which submicrocracks appear, called by L. M. Rybakova the stress of destruction of.…”

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confidence: 99%

Analysis of the process of damage cumulation on various scale levels

1997

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It is known that the structure of the material plays a decisive role in the stage of initiation of fracture that is connected with formation of multiple pores and cracks. This stage has been studied less than the stage of development of a localized microcrack, which is described in terms of fracture mechanics. However, in order to optimize the structure of metals and alloys we should understand the laws governing the cumulation of discontinuities in the stage of the appearance of a trunk crack at various structural levels. This will allow us to relate the parameters of the structure with the characteristics of the process of cumulation of pores and microcracks and thus provide a basis for developing new materials with a high fracture resistance in the initial stage of fracture and for damage diagnostics by methods of nondestructive testing. It should be noted that analysis of damage cumulation is also of interest from the standpoint of the general laws of the fracture process in various materials, including metals, nonmetals, and rocks, because much experimental data show that these laws are similar and independent of the nature of the material and the scale level considered.Cumulation of discontinuities is studied [1-5 etc.] within the framework of the intensely developing field of damage mechanics, based on the universally acknowledged concept of vulnerability to damage introduced by L. M. Kachanov [6] and Yu. N. Rabotnov [7]. According to this concept the level of damage m is determined from the relative area of cracks or pores cumulated at the source of fracture in the specimen in the process of loading. It is assumed that at the initial moment the vulnerability to damage is equal to zero, and at the moment of failure it is equal to unity. It is difficult to evaluate the intermediate cases, but L. M. Kachanov has suggested using the following kinetic equation based, as he puts it, on the concepts of statistical physics for estimating the progress of damage:where cr is the stress, T is the temperature, and r is the time. The variables may include parameters characterizing the deformation and internal structure of the material. The solution of the suggested differential equation with respect to the rate of cumulation of defects is complicated by the dependence of the function F on numerous factors that determine the load-I A. A. Baikov Institute of Metallurgy of the Russian Academy of Sciences, Moscow, Russia; International Institute of the Theory of Earthquake Prediction and Mathematical Geophysics of the Russian Academy of Sciences, Moscow, Russia.ing conditions. For this reason, the rate of damage is described either by cumbersome semi-empirical equations relating this parameter to basic mechanical properties or by relations that determine the damage as a certain function of the relative endurance of the material. Most often the rate of cumulation of discontinuities is described by a power or exponential function of the form dm/dt -(1 -m) p (cy/cl0)" ;where p and n are dimensionless constants, k is Boltzma...

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Plastic deformation beyond the ultimate strength

Cited by 2 publications

References 2 publications

Behavior of hydrogen in fracture and friction of metals and alloys

Behavior of hydrogen in fracture and friction of metals and alloys

Analysis of the process of damage cumulation on various scale levels

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