Computation and experimental investigation of the resistance of steels to plastic deformation and failure under a non-stationary repeating-static load

The structural model of a material and the corresponding equation of mechanical states for strain calculation in a complex cyclic stress state are presented. Present computational and theoretical data are compared with those obtained by authors of other studies. An energy-type damage equation is presented. The results of computation in accordance with this equation are compared with some experimental data obtained on tubular specimens in a complex stress state.Translated from Problemy Prochnosti, No. 4, pp. 3–7, April, 1991.     

Effect of laser microalloying with niobium on the wear resistance of stainless steels

We have studied the effect of laser alloying of 20Kh13 and 12Kh18N10T steels with niobium on their physicochemical properties. Microalloyed surface layers of thickness more than 350 μm, enriched with niobium, carbon, and oxygen in the solid solution and separate oxycarbide inclusions, were formed by means of laser treatment. The microhardness of the external layers of steels becomes 2–3 times higher (up to 7.1–7.7 GPa). Laser alloying reduces the wear of 20Kh13 steel by a factor of 5–6 under a contact pressure of 0.29 MPa and cuts it in half under 0.42 MPa. The wear of 12Kh18N10T steel is reduced by a factor of 2–3. We have also proposed a scheme of the wear of steels, according to which their wear resistance increases owing to the formation of hardened surface layers, where the oxycarbide inclusions exert a reinforcing action on the more plastic solid solution of niobium, carbon, and oxygen in iron.     

Kinetics of scattered fracture in structural metals under elastoplastic deformation

The paper presents a procedure whereby the damage accumulation kinetics in structural materials, such as steel 45, stainless steel 12Kh18N10T, aluminum alloy D16T, and titanium alloy VT22, under elastoplastic deformation is studied based on variation parameters of elastic modulus and resistivity. For complex stress conditions, a continuum model for damage accumulation is proposed which relates the damage parameter to the intensity of accumulated plastic strains. The data calculated by the proposed continuum model are compared to the experimental findings of the investigation of the damage accumulation kinetics for some structural metals. __________ Translated from Problemy Prochnosti, No. 3, pp. 23–34, May–June, 2007.     

Effect of aging and cold working on the resistance to plastic deformation of structural steels under low-cycle loading

Conclusions Experiments with steels 22K and TS showed that aging after preliminary plastic deformation leads to an increase of the yield strength in reverse loading. Large preliminary plastic deformation with Tage =const and an increase of the aging temperature with _pre=const lead to an increase in the effect of aging. In the first cycles of loading one observes a reduction of _T ^' and then stable values. The stable value of _T ^' for aged samples is above that of the original in all cases where the stress in the cycle does not exceed the maximum stress in preliminary deformation. Removal of the surface layer increases the effect of aging.Institute of Mechanical Sciences, Moscow. Translated from Problemy Prochnosti, No. 1, pp. 42–45, January, 1970.     

Effect of previous plastic deformation on the resistance of chromium-manganese steels to cavitation erosion

The investigation described in this paper was concerned with austenitic chromium-manganese steels characterized by various resistances to the martensitic transformation during plastic deformation. It was established that the influence of previous plastic deformation on the resistance of these steels to cavitation erosion varies. In each case it is necessary to consider both the susceptibility of austenite to decomposition (accompanied by the formation of martensite and -phase) under the influence of cavitation and various phase and structural transformations taking place in the steel as a result of previous plastic deformation.     

Influence of the pliability of a testing machine on the resistance of metals to deformation in the case of jump-like development of their elastoplastic deformation

We analyze the influence of the stiffness of a testing machine and the loading mode on the mechanical characteristics and resistance of metals to deformation in the case of nonmonotonic development of their elastoplastic deformation caused by cooling to 4.2 K and (or) the action of pulses of electric current. We propose an approach that enables one to reduce the value of a jump of loading caused by the action of a pulse of electric current for an arbitrary loading mode to the maximum possible value (for a constant strain rate and a small amount of elastic energy accumulated by a loading device). Institute of Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 3, pp. 125–132, May–June, 2000.     

Numerical modeling of elastoplastic deformation and damage accumulation in metals under low-cycle fatigue conditions

A mathematical model that describes the processes of fatigue damage accumulation in structural materials (metals and alloys) under multiaxial disproportionate combined thermomechanical loading is advanced from the standpoint of the damaged medium mechanics. Based on the results of basic experiments performed in a special way, an experimental-theoretical procedure for finding material parameters of the advanced constitutive relations of the damaged medium mechanics is put forward. The advanced version of the constitutive relations of the damaged medium mechanics is shown to adequately (qualitatively and quantitatively) reflect the main effects of elastoplastic deformation and damage accumulation in metals under low-cycle fatigue.     

Effect of Mn on strain accumulation in Nb microalloying steels

High Mn is added in line pipe steels to strengthen them. Also, Mn lowers the phase transformation temperature, which is an advantage because it lowers the rolling temperature for grain size control. However, Mn retards the kinetics of precipitation of NbC in thermo-mechanical processing in Nb microalloying steels. In high-grade line pipe steels, the control of strain accumulation behavior is the key to the control of grain size. Strain accumulation can only be obtained when static recrystallization between passes could be suppressed. The effect of NbC precipitates on suppressing recrystallization has been widely investigated, mostly focusing on the Zener pinning of NbC on grain boundaries. However, it is applicable in large strain and long inter-pass time. In short inter-pass time, such as strip mill rolling, recrystallization behavior is controlled by the complicated interaction of precipitation with recovery and recrystallization. In this paper, the effect of Mn on strain accumulation during multi-pass strip mill rolling based on the interaction of precipitates with the activation energy of grain boundary migration and recovery, and the thermodynamics and kinetics of recrystallization are discussed systematically.     

Experimental investigation of a variant of the theory of elastoplastic deformation of metals under complex loading

The article presents analytical approximations of two scalar functionals of the ternary relation of the theory of elastoplastic processes containing, in addition to the function of simple loading, four constants of plasticity of the material which are determined from experiments with bilinear strain paths with an orthogonal corner. It also presents the results of a comparison with the data of experiments with complex loading along variegated two- and three-dimensional strain paths that make it possible to assume the applicability of the suggested defining equations for describing processes of a single (with possible unloading) arbitrarily complex loading of initially isotropic strain-hardening materials.Translated from Problemy Prochnosti, No. 12, pp. 48–53, December, 1990.     

Effect of cyclic deformation on the resistance of a material to brittle failure

A physicomechanical model is suggested for determining the critical brittle failure stress S_c in statically and cyclically deformed material. The model is based on ideas about retardation of microcracks in a deformed substructure which changes during material loading. The effect is determined by experiment of prior cyclic material deformation on resistance to cleavage. The calculated dependence of S_c on the Odquist parameter is compared with the experimental results obtained. Model ideas about the effect of material substructure on brittle failure are confirmed by fractographic studies. Unstable fatigue crack growth is studied on the basis of models for brittle and fatigue failure of BCC-metals.Translated from Problemy Prochnosti, No. 1, pp. 14–21, January, 1991.