Vector variant of a strain-hardening hypothesis and kinetic equations of high-temperature creep

1981 ◽  
Vol 13 (1) ◽  
pp. 30-35
Author(s):  
A. L. Arshakuni
Keyword(s):  
High Temperature ◽  
Strain Hardening ◽  
Kinetic Equations ◽  
High Temperature Creep ◽  
Temperature Creep ◽  
Vector Variant

scholarly journals NUMERICAL STUDY OF THE PROCESS OF HIGH-TEMPERATURE CREEP AND LONG-TERM STRENGTH OF STRUCTURAL ALLOYS UNDER UNIAXIAL TENSION

2021 ◽  
Vol 83 (3) ◽  
pp. 294-310
Author(s):  
I.V. Smetanin
Keyword(s):  
High Temperature ◽  
Damage Accumulation ◽  
Kinetic Equations ◽  
Structural Materials ◽  
High Temperature Creep ◽  
Term Strength ◽  
Thermomechanical Loading ◽  
Initial Strength ◽  
Temperature Creep

The main regularities of deformation processes are consideredand degradation of the initial strength properties of structural materials (metals and their alloys) by the mechanism of long-term strength. To describe the processes of high-temperature creep and long-term strength of polycrystalline structural alloys, an approach based on the concept of “hidden” or “internal” parameters is used, which can give a qualitative and quantitative description of experimental data. This approach has two important advantages: it allows you to cover a wide range of behavior of structural materials and at the same time it is very convenient for analyzing the stress-strain state. The mathematical model of the mechanics of a damaged medium used in this work, describing the processes of inelastic deformation and damage accumulation during creep, consists of three interrelated components: evolutionary relations that determine the inelastic behavior of the material, considering the dependence on the destruction process; kinetic equations describing the process of damage accumulation; criteria for the strength of the damaged material. The variant of the determining relations of viscoplastic deformationof polycrystalline structural alloys is based on the idea of the existence of a family of equipotential creep surfaces in the stress space and the principle of gradiency of the creep strain rate vector to the corresponding surface at the loading point.This version of the equations of state reflects the main regularitiesthe process of viscoplastic deformation of the material under proportional and disproportionate modes of combined thermomechanical loading. The variant of the kinetic equations of damage accumulation is based on theintroduction of a scalar damage parameter, is based on energy principles, and considers the main effects of the formation, growth and fusion of microdefects for arbitrary complex modes of thermomechanical loading. As a criterion of the strength of the damaged material, the condition for reaching the critical value of the damage value is used. The results of experimental studies of short-term high-temperature creep of several structural alloys (copper, stainless steel X18H10T) at constant temperature values and various levels of forces set in the samples are presented. To assess the degree of reliability and determine the limits of applicabilitymodels of the mechanics of the damaged medium numerical studies of the process of high-temperature creep and long-term strength of these structural alloys are carried out and the numerical results obtained are compared with the data of field experiments. The results of comparing the calculated and experimental data allow us to conclude that the proposed determining relationships are reliable when the initial strength properties of structural materials are degraded by the mechanism of long-termstrength. It is shown that the model used qualitatively and with the accuracy necessary for practical calculations quantitatively describes the main effects of the process of viscoplastic deformation and damage accumulation in polycrystalline structural alloys under high-temperature thermomechanical loading.

scholarly journals On the Plastic Strain Accumulation in Notched Bars During High-Temperature Creep Dwell

2020 ◽  
Vol 36 (2) ◽  
pp. 167-176 ◽  
Author(s):  
Daniele Barbera ◽  
Haofeng Chen
Keyword(s):  
High Temperature ◽  
Cyclic Loading ◽  
Plastic Strain ◽  
Kinematic Hardening ◽  
High Temperature Creep ◽  
Strain Accumulation ◽  
Material Models ◽  
Cyclic Loading Condition ◽  
Hardening Material ◽  
Temperature Creep

ABSTRACTStructural integrity plays an important role in any industrial activity, due to its capability of assessing complex systems against sudden and unpredicted failures. The work here presented investigates an unexpected new mechanism occurring in structures subjected to monotonic and cyclic loading at high temperature creep condition. An unexpected accumulation of plastic strain is observed to occur, within the high-temperature creep dwell. This phenomenon has been observed during several full inelastic finite element analyses. In order to understand which parameters make possible such behaviour, an extensive numerical study has been undertaken on two different notched bars. The notched bar has been selected due to its capability of representing a multiaxial stress state, which is a practical situation in real components. Two numerical examples consisting of an axisymmetric v-notch bar and a semi-circular notched bar are considered, in order to investigate different notches severity. Two material models have been considered for the plastic response, which is modelled by both Elastic-Perfectly Plastic and Armstrong-Frederick kinematic hardening material models. The high-temperature creep behaviour is introduced using the time hardening law. To study the problem several results are presented, as the effect of the material model on the plastic strain accumulation, the effect of the notch severity and the mesh element type and sensitivity. All the findings further confirm that the phenomenon observed is not an artefact but a real mechanism, which needs to be considered when assessing off-design condition. Moreover, it might be extremely dangerous if the cyclic loading condition occurs at such a high loading level.

Investigation of High-Temperature Creep in Mullite – Zirconium Oxide Polydisperse Ceramic

2014 ◽  
Vol 71 (5-6) ◽  
pp. 175-179
Author(s):  
V. G. Maksimov ◽  
D. V. Grashchenkov ◽  
V. A. Lomovskoi ◽  
V. G. Babashov ◽  
O. V. Basargin ◽  
...  
Keyword(s):  
High Temperature ◽  
Zirconium Oxide ◽  
High Temperature Creep ◽  
Temperature Creep
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