scholarly journals Evaluation of fatigue life of polycrystalline structural alloys

2018 ◽  
Vol 226 ◽  
pp. 03021
Author(s):  
Ivan A. Volkov ◽  
Leonid A. Igumnov ◽  
Aleksandr A. Ipatov
Keyword(s):  
Plastic Deformation ◽  
Damage Accumulation ◽  
Failure Process ◽  
Block Type ◽  
Elastoplastic Behavior ◽  
Evolutionary Equations ◽  
Defining Relations ◽  
Cycle Loading ◽  
Main Effects ◽  
Kinetics Of

A mathematical model describing the processes of elastoplastic deformation and damage accumulation under low-cycle loading has been developed, based on the viewpoint of mechanics of damaged media (MDM). The MDM model consists of three interrelated parts: defining relations describing elastoplastic behavior of the materials, taking into account its dependence on the failure process; evolutionary equations describing the kinetics of damage accumulation; strength criteria of the damaged material. In order to assess the reliability and scope of applicability of the defining relations of mechanics of damaged media, the processes of plastic deformation and damage accumulation in variety of structural steels in low-cycle tests have been numerically analyzed, and numerical results obtained have been compared with the data of full-scale experiments. It is shown that the presented model of mechanics of damaged media adequately describes, both qualitatively and quantitatively, with accuracy, necessary for practical calculations, the main effects of the processes of plastic deformation and damage accumulation in structural alloys under block-type non-stationary non-symmetrical low-cycle loading.

scholarly journals NUMERICALLY MODELING FATIGUE LIFE OF STRUCTURAL ELEMENTS UNDER THERMAL CYCLIC LOADING

2020 ◽  
Vol 82 (2) ◽  
pp. 168-188
Author(s):  
I.A. Volkov ◽  
L.A. Igumnov ◽  
D.N. Shishulin ◽  
V.A. Eremeev
Keyword(s):  
Plastic Deformation ◽  
Fatigue Life ◽  
Fatigue Damage ◽  
Damage Accumulation ◽  
Strength Criterion ◽  
Cyclic Fatigue ◽  
Defining Relations ◽  
Damage Degree ◽  
Fatigue Damage Accumulation ◽  
Main Effects

The paper considers processes of fatigue life of materials and structures in the exploitation conditions characterized by multiparametric nonstationary thermal-mechanical effects In the framework of mechanics of damaged media, a mathematical model is developed that describes processes of thermal-plastic deformation and fatigue damage accumulation in materials with degradation according to low- and high-cycle fatigue mechanisms (accounting for their interaction). The model consists of three interconnected parts: relations determining cyclic thermal-plastic behavior of a material, accounting for its dependence on the failure process; equations describing kinetics of fatigue damage accumulation; a strength criterion of the damaged material. The version of the defining relations of thermal plasticity is based on the notion of the yield surface and the principle of orthogonality of the plastic strain rate vector to the yield surface at the loading point and reflects the main effects of the process of cyclic plastic deformation of the material for arbitrarily complex trajectories of combined thermal-mechanical loading. The version of kinetic equations of fatigue damage accumulation is based on introducing a scalar parameter of damage degree and on energy-based principles, and takes into account the main effects of the nucleation, growth and merging of microdefects under arbitrarily complex loading regimes. A generalized form of an evolutionary equation of fatigue damage accumulation in low-cycle and high-cycle fatigue regions is introduced. The condition when the damage degree reaches its critical value is taken as the strength criterion of the damaged material. To assess the reliability and the scope of applicability of the developed defining relations of mechanics of damaged media, processes of thermal-plastic deformation and fatigue damage accumulation have been numerically analyzed, and the numerical results obtained have been compared with the data of full-scale experiments for a particular applied problem. The effect of the dropping frequency of a distillate on thermal cyclic fatigue life of the material of a heated surface of a tube has been numerically analyzed. The computational results for the fatigue damage accumulation processes under thermal pulsed loading are compared with experimental data. It is shown that the developed model describes both qualitatively and, accurately enough for engineering purposes, quantitatively the experimental data and can be effectively used for evaluating thermal-cyclic fatigue life of structures working in the conditions of multiaxial non-proportional regimes of combined thermal-mechanical loading.

scholarly journals MODELING PLASTIC DEFORMATION OF POLYCHRYSTALLINE STRUCTURAL ALLOYS UNDER BLOCK-TYPE NONSYMMETRICAL REGIMES OF SOFT LOW-CYCLE LOADING

2019 ◽  
Vol 81 (1) ◽  
pp. 63-76
Author(s):  
I. A. Volkov ◽  
L. A. Igumnov ◽  
I. S. Tarasov ◽  
D. N. Shishulin ◽  
S. N. Pichkov ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Experimental Studies ◽  
Hysteresis Loops ◽  
Isotropic Hardening ◽  
Block Type ◽  
Deformation Model ◽  
Plasticity Model ◽  
Defining Relations ◽  
Thermal Plasticity ◽  
Cycle Loading

Processes of plastic deformation of polycrystalline structural alloys under block-type nonstationary regimes of soft low-cycle loading are considered. Modified Korotkikh's thermal-plasticity model pertaining to the class of yield theories with translation-isotropic hardening is used as defining relations of plasticity. The modification of Korotkikh's model consists in using a different formulation of evolutionary equations for the displacement of the yield surface center (the micro-stress tensor), used for block-type nonstationary regimes of low-cycle loading for describing effects of setting under a hard loading regime (controlled strains) and ratcheting under a soft loading regime (controlled stresses) of the plastic hysteresis loop. Determining the material parameters and scalar functions of the plastic deformation model, assessing its adequacy and scope of application was done based on the experimental studies of the deformation process of laboratory specimens made of stainless steels of the austenite (SS316L, SS304) and ferrite (20MnMoNi5-5) classes in the conditions of uniaxial and multiaxial, proportional and non-proportional regimes of soft block-type cyclic loading. Comparison of the numerical results with the experimental data indicates that the developed plasticity model qualitatively and quantitatively, accurately enough for engineering purposes, describes the main effects of plastic deformation (displacements of the plastic hysteresis loops and decreasing strain amplitudes) under block-type nonstationary nonsymmetrical regimes of soft low-cycle loading.

scholarly journals Kinetics of deformation and damage accumulation in concentration zones with nonisothermal low-cycle loading

1985 ◽  
Vol 17 (8) ◽  
pp. 1050-1056
Author(s):  
A. G. Kazantsev ◽  
A. P. Gusenkov ◽  
A. N. Chernykh
Keyword(s):  
Damage Accumulation ◽  
Cycle Loading ◽  
Kinetics Of

Study of the regularities of resistance to deformation and damage accumulation under irregular low cycle loading

2021 ◽  
Vol 87 (11) ◽  
pp. 55-63
Author(s):  
M. M. Gadenin
Keyword(s):  
Elastoplastic Deformation ◽  
Damage Accumulation ◽  
Low Cycle Fatigue ◽  
Functional Dependence ◽  
Experimental Studies ◽  
Similar Data ◽  
Cycle Loading ◽  
Cyclic Elastoplastic Deformation ◽  
Loading Modes ◽  
Kinetics Of

The results of computation and experimental studies of changes in the regularities of the strain resistance and damage accumulation in conditions of the irregular low cycle loading are presented and compared with similar data for a regular cyclic elastoplastic deformation at the same loading. The irregular mode of low cycle loading implemented in the study is adopted in the form of an equiprobable distribution of changes in the stress amplitudes within a given range between maximum and minimum levels at the symmetric form of the cycles. This mode was reproduced on test equipment through introduction of the corresponding functional dependence of changes in the stress amplitude in the cycles into the control program. The data on a cycle-by-cycle kinetics of both cyclic and unilaterally accumulated strains obtained under irregular mode of loading were recorded in a databank and then compared with the data for a regular loading. This provided the possibility of their analytical description by the corresponding equations of state with the correction of the parameters of the diagrams of cyclic elastoplastic deformation taking into account the conditions of irregularity of loading modes. The results of the experiments are presented in the form of diagrams of the tests modes, curves of a low cycle fatigue of the studied material at the soft and hard loading modes, diagrams of a cycle-by-cycle kinetics of the cyclic and accumulated strains at the regular and irregular modes, and also as kinetic diagrams of damages accumulation for these conditions. Using the summation criteria expressed through the deformation characteristics of accumulated damage, it is shown that taking into account change in the character of the strain development under irregular low-cycle loading, the criterion dependences can be used to assess the durability and compare it with the similar data under regular modes when accepting the condition of attaining the limiting state.

Modeling Plastic Deformation of Structural Alloys under Block-Type Nonsymmetrical Regimes of Low-Cycle Loading

2019 ◽  
Vol 40 (11) ◽  
pp. 2018-2026
Author(s):  
I. A. Volkov ◽  
L. A. Igumnov ◽  
I. S. Tarasov ◽  
D. N. Shishulin
Keyword(s):  
Plastic Deformation ◽  
Block Type ◽  
Cycle Loading

scholarly journals MODELING FATIGUE LIFE OF POLYCRYSTALLINE STRUCTURAL ALLOYS UNDER A COMBINED EFFECT OF LOW- AND HIGH-CYCLE FATIGUE MECHANISMS

2019 ◽  
Vol 81 (3) ◽  
pp. 305-323
Author(s):  
I.A. Volkov ◽  
L.A. Igumnov ◽  
S.N. Sikaryov ◽  
D.N. Shishulin ◽  
A.I. Volkov
Keyword(s):  
Plastic Deformation ◽  
Fatigue Damage ◽  
Damage Accumulation ◽  
High Cycle Fatigue ◽  
Strength Criterion ◽  
Combined Effect ◽  
Evolutionary Equation ◽  
Cycle Fatigue ◽  
Fatigue Damage Accumulation ◽  
Main Effects

Processes of fatigue life of polycrystalline structural alloys under a combined effect of low- and high-cycle fatigue are considered. In the framework of mechanics of damaged media (MDM), a mathematical model is developed, which describes processes of plastic deformation and fatigue damage accumulation. The MDM model consists of three interrelated parts: relations defining cyclic elastoplastic behavior of the material, accounting for its dependence on the failure process; equations describing fatigue damage accumulation kinetics; a strength criterion of the damaged material. The version of defining relations of elastoplasticity is based on the notion of yield surface and the principle of orthogonality of the plastic strain rate vector to the yield surface at the loading point. This version of equations of state reflects the main effects of the cyclic plastic deformation process of the material for arbitrarily complex loading trajectories. The version of kinetic equations of damage accumulation is based on introducing a scalar parameter of damage degree. The construction uses energy-based principles and accounts for the main effects of the process of nucleation, growth and merging of microdefects under arbitrarily complex multiaxial loading regimes. A combined form of the evolutionary equation of fatigue damage accumulation in the regions of low-cycle (LCF) and high-cycle (HCF) fatigue is proposed. It is shown that, under regular cyclic loading of the material, the stress amplitude of the cycle decreases by degrees during the transition from LCF to HCF and depends on the physical interaction of these mechanisms in the transition zone. The condition when the damage degree attains its critical value is taken as the strength criterion of the damaged material. A methodology of numerically determining parameters of the evolutionary equation of fatigue damage accumulation in the conditions of HCF is presented. To assess the reliability and the limits of applicability of the defining relations of MDM, processes of plastic deformation and fatigue damage accumulation in a number of structural alloys in cyclic tests have been numerically studied, and the obtained numerical results have been compared with the data of full-scale experiments. The results of comparison of the numerical and experimental data reveal that the developed model of mechanics of damaged media adequately describes durability of structures subjected to a combined effect of low- and high-cycle fatigue mechanisms. It is shown that the introduced MDM model qualitatively and, accurately enough for practical engineering purposes, quantitatively describes the main effects of the processes of plastic deformation and fatigue damage accumulation in structural alloys under cyclic loading.

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