Special features of the deformation kinetics of structural materials in cyclic elastoplastic deformation

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.

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Features of the kinetics of cyclic elastoplastic deformation diagrams at dwells in cycles and superimposition of variable stresses on them

Industrial laboratory Diagnostics of materials ◽

10.26896/1028-6861-2020-86-12-46-53 ◽

2020 ◽

Vol 86 (12) ◽

pp. 46-53

Author(s):

M. M. Gadenin

Keyword(s):

Experimental Data ◽

Elastoplastic Deformation ◽

Low Cycle Fatigue ◽

Cycle Fatigue ◽

Loading Cycle ◽

Additional Variable ◽

Dynamic Creep ◽

Variable Stresses ◽

Kinetics Of ◽

Deformation Diagrams

The goal of the study is determination of the regularities of changes in cyclic strains and related deformation diagrams attributed to the existence of time dwells in the loading modes and imposition of additional variable stresses on them. Analysis of the obtained experimental data on the kinetics of cyclic elastoplastic deformation diagrams and their parameters revealed that in contrast to regular cyclic loading (equal in stresses), additional deformations of static and dynamic creep are developed. The results of the studys are especially relevant for assessing the cyclic strength of unique extremely loaded objects of technology, including nuclear power equipment, units of aviation and space systems, etc. The experiments were carried out on the samples of austenitic stainless steel under low-cycle loading and high temperatures of testing. Static and dynamic creep deformations arising under those loading conditions promote an increase in the range of cyclic plastic strain in each loading cycle and also stimulate an increase in the range of elastoplastic strain due to active cyclic deformation. At the same time the existence of dwells on extrema of stresses in cycles without imposition of additional variable stresses on them most strongly affects the growth of plastic strain ranges in cycles. Imposition of additional variable stresses on dwells also results in the development of creep strains, but their growth turns out to be somewhat less than in the presence of dwells without stresses imposed. The diagrams of cyclic deformation obtained in the experiments are approximated by power dependences, their kinetics being described in terms of the number of loading cycles using corresponding temperature-time functions. At the same time, it is shown that increase in the cyclic plastic deformation for cycles with dwells and imposition of additional variable stresses on them decreases low cycle fatigue life compared to regular loading without dwells at the same stress amplitudes, moreover, the higher the values of static and dynamic creep, the greater decrease in low-cycle fatigue life. This conclusion results from experimental data and analysis of conditions of damage accumulation for the considered forms of the loading cycle using the deformation criterion of reaching the limit state leading to fracture.

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Physical characteristic features of the deformation kinetics of foam plastics

Mechanics of Composite Materials ◽

10.1007/bf00608369 ◽

1986 ◽

Vol 22 (3) ◽

pp. 379-383

Author(s):

A. G. Dement'ev ◽

O. G. Tarakanov

Keyword(s):

Physical Characteristic ◽

Deformation Kinetics ◽

Characteristic Features ◽

Kinetics Of ◽

Foam Plastics

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INHOMOGENEOUS LARGE DEFORMATION KINETICS OF POLYMERIC GELS

International Journal of Applied Mechanics ◽

10.1142/s1758825113500014 ◽

2013 ◽

Vol 05 (01) ◽

pp. 1350001 ◽

Cited By ~ 45

Author(s):

WILLIAM TOH ◽

ZISHUN LIU ◽

TENG YONG NG ◽

WEI HONG

Keyword(s):

Large Deformation ◽

Soft Matter ◽

Inner Core ◽

Kinetic Studies ◽

Fe Model ◽

One Dimensional ◽

Simplified Approach ◽

Deformation Kinetics ◽

Polymeric Gels ◽

Kinetics Of

This work examines the dynamics of nonlinear large deformation of polymeric gels, and the kinetics of gel deformation is carried out through the coupling of existing hyperelastic theory for gels with kinetic laws for diffusion of small molecules. As finite element (FE) models for the transient swelling process is not available in commercial FE software, we develop a customized FE model/methodology which can be used to simulate the transient swelling process of hydrogels. The method is based on the similarity between diffusion and heat transfer laws by determining the equivalent thermal properties for gel kinetics. Several numerical examples are investigated to explore the capabilities of the present FE model, namely: a cube to study free swelling; one-dimensional constrained swelling; a rectangular block fixed to a rigid substrate to study swelling under external constraints; and a thin annulus fixed at the inner core to study buckling phenomena. The simulation results for the constrained block and one-dimensional constrained swelling are compared with available experimental data, and these comparisons show a good degree of similarity. In addition to this work providing a valuable tool to researchers for the study of gel kinetic deformation in the various applications of soft matter, we also hope to inspire works to adopt this simplified approach, in particular to kinetic studies of diffusion-driven mechanisms.

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Elastic Modulus of Pb/Sn Solder Joints in Microelectronics

Electronic and Photonic Packaging, Electrical Systems Design and Photonics, and Nanotechnology ◽

10.1115/imece2002-39632 ◽

2002 ◽

Author(s):

Cemal Basaran ◽

Jianbin Jiang

Keyword(s):

Grain Size ◽

Elastic Modulus ◽

Single Crystal ◽

Solder Alloy ◽

Ultrasonic Testing ◽

Heterogeneous Materials ◽

Testing Methods ◽

Nano Indentation ◽

Deformation Kinetics ◽

Kinetics Of

Young’s modulus (E) values published in literature for the eutectic Pb37/Sn63 and near eutectic Pb40/Sn60 solder alloy vary significantly. One reason for this discrepancy is different testing methods for highly rate sensitive heterogeneous materials, like Pb/Sn alloys, yield different results. In this paper, we study different procedures used to obtain the elastic modulus; analytically, by single crystal elasticity and experimentally by ultrasonic testing and Nano indentation. We compare these procedures and propose a procedure for elastic modulus determination. The deformation kinetics of the Pb/Sn solder alloys is discussed at the grain size level.

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