Effect of short-term cyclic overloads on the fatigue strength and damping capacity of carbon steels

Gur'ev, A. V.; Савкин, А. Н.

doi:10.1007/bf01521095

Strength Mater

1978

DOI: 10.1007/bf01521095

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Effect of short-term cyclic overloads on the fatigue strength and damping capacity of carbon steels

A. V. Gur'ev¹,

А. Н. Савкин²

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2008

2009

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Cited by 3 publications

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“…The specific feature of the stage of dispersed damages is the separation of the incubation period, in which the accumulation of damage does not occur. As is well known, the hardening of structural components of metals is possible during this period [10,11]. For example, after short-term cyclic overloading of steels on a moderate level, an increase in their durability is observed under fairly low subsequent cyclic loading [11].…”

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Comparative analysis of models of accumulation of dispersed damages in metals under irregular variable loading

Bagmutov

Савкин

2009

Strength Mater

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We analyze models of summation of fatigue damages under irregular variable loading on the basis of linear and nonlinear interpretation of the damage function. We show the necessity of taking into account the main physicomechanical processes in the metal under cyclic loading, which can improve the accuracy of computations.Keywords: models of summation of fatigue damages, physicomechanical processes, cyclic loading.The demands of engineering practice in designing new and perfecting the existing technical articles that work under regular and irregular variable loading, as well as the introduction of new promising materials, require the development of models and computational methods that would enable one to better predict the durability of an engineering object under in-service conditions for guaranteeing its high reliability and competitiveness [1,2]. In doing so, it is important both to carry out a comparative analysis of existing models and to develop new models (especially those available for engineering practice) with regard for the actual mechanisms of damage accumulation, improving the accuracy of prediction.The solution of such a complex problem is connected with searching for the most general laws describing the kinetics of damage accumulation in metals. Note that the intention to take into account the phenomena occurring in the structure of metals more accurately leads to the complication of the existing relations. One of the approaches in the theory of summation of fatigue damages is the concept of crack initiation and growth, which has found its reflection in the models of summation where fatigue consists of two stages.The first of them, i.e., the stage of crack initiation, or the development of dispersed damages, is connected with the kinetics of accumulation of microplastic strains, which lead to the development of damages in the form of short dispersed cracks. When the critical point is achieved, the process of damage passes to the second stage, namely, the propagation and growth of a main crack, which, upon reaching its critical length, leads to the fracture of the material or of the structural element. According to another approach, a defect in the form of a crack can always be present in the structure of a metal, especially in the case of stress concentration, and, therefore, one should consider durability as the survivability of a cracked structure, whose lifetime is determined by the kinetics of crack propagation up to reaching its critical size. Such a concept is appropriate for structural elements in operation, especially for preventive measures and for the determination of their lifetime resource. Depending on operational, technological, and design factors, this stage can constitute 10 to 30% of the lifetime of the structure [3].In the present work, we consider the problem of evaluating the durability of materials and structural elements in the stage of dispersed damages (the stage that determines the main lifetime of the structure under consideration up to its failure). In engineering practic...

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“…. (2) nonlinear model (7); (3) nonlinear model with regard for the stage character and the decrease in the endurance limit of the material (9)-(11); (4) linear model with regard for the decrease in the endurance limit (10) and (11). Here, J sà = 0 05 .…”

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Comparative analysis of models of accumulation of dispersed damages in metals under irregular variable loading

Bagmutov

Савкин

2009

Strength Mater

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“…Imperfection of a polycrystal material structure results in its nonuniform stressed state during loading. Therefore, stress values in local volumes of a material can exceed the nominal ones in two-three times [2][3][4], which results in the inhomogeneous process of plastic deformation in the total volume of a polycrystal material.Under cyclical loading conditions, microplastic strain is one of major factors of variation of mechanical characteristics. Inelastic strain per cycle is used as a quantitative characteristic of microplastic deformation process.…”

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confidence: 99%

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“…This phenomenon is known as the Bauschinger effect [8], which implies strain-hardening or strain-softening under cyclic loading conditions. Stressed state nonuniformity can be expressed by the statistical distribution characteristic of microplastic strains [2,3]. The microplastic deformation kinetics must correspond to the pattern of the material damage accumulation as long as varies the fatigue localization volume.…”

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Inelasticity monitoring of structural materials by the resonance method

Mailo

2009

Strength Mater

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We have developed a method which provides monitoring of the inelasticity kinetics of polycrystal materials by variation of the stress-strain phase-shift angle in the locally loaded surface zone of the material under study. The proposed method allows one to determine current value of damage of investigated aluminum alloy under laboratory conditions of cyclic deformation by variation of statistical characteristics of phase-shift angle distribution. AMg6N aluminum alloy, which is a cyclically hardening material, was used in this study.All structural materials during deformation manifest dissipation of mechanical characteristics due to imperfection of the material structure stipulated by presence of acute angles, lattice defects, asymmetry of structural elements, etc. These factors are stress concentrators on macro-, micro-, and submicroscopic levels. Results of [1] provide a quantitative assessment of a size of a structural element (grain) in a volume of the investigated polycrystal material. Grain dimensions can vary by order of magnitude, while those of grain units -in several times. Imperfection of a polycrystal material structure results in its nonuniform stressed state during loading. Therefore, stress values in local volumes of a material can exceed the nominal ones in two-three times [2][3][4], which results in the inhomogeneous process of plastic deformation in the total volume of a polycrystal material.Under cyclical loading conditions, microplastic strain is one of major factors of variation of mechanical characteristics. Inelastic strain per cycle is used as a quantitative characteristic of microplastic deformation process. In stress-strain coordinates, variation of mechanical characteristics of a material during cyclical loading is described by a closed hysteresis loop. The loop width is proportional to the inelastic strain per cycle, which makes possible quantitative estimation of a polycrystal material damageability [5][6][7]. Under cyclic loading conditions, the stress distribution in a structural material attributed to its imperfection varies cycle by cycle, which results in reduction of the material proportionality and yield stress limits. This phenomenon is known as the Bauschinger effect [8], which implies strain-hardening or strain-softening under cyclic loading conditions. Stressed state nonuniformity can be expressed by the statistical distribution characteristic of microplastic strains [2,3]. The microplastic deformation kinetics must correspond to the pattern of the material damage accumulation as long as varies the fatigue localization volume. There are many methods which provide integral estimation of inelastic strains in a material per cycle: calorimetric method [9], phase method [10], the method of free damped oscillations [11], the Kimball-Lazan method [12], resonance curve method [13], and the dynamic hysteresis loop method [10]. A deficiency of the above methods is that the integral material inelasticity characteristic fails to provide comprehensive description of the material structur...

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Estimating the life of material with an irregular load

Savkin

2008

Russ. Engin. Res.

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Effect of short-term cyclic overloads on the fatigue strength and damping capacity of carbon steels

Cited by 3 publications

References 0 publications

Comparative analysis of models of accumulation of dispersed damages in metals under irregular variable loading

Comparative analysis of models of accumulation of dispersed damages in metals under irregular variable loading

Inelasticity monitoring of structural materials by the resonance method

Estimating the life of material with an irregular load

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