A Physically Based Constitutive Equation for Creep-Damaging Solids

1985 ◽  
Vol 52 (3) ◽  
pp. 615-620 ◽  
Author(s):  
A. J. Levy
Keyword(s):  
Constitutive Equation ◽  
Grain Boundary ◽  
Elevated Temperatures ◽  
Cavity Growth ◽  
Internal Variable ◽  
Nucleation And Growth ◽  
Creep Model ◽  
Steady Creep ◽  
Physically Based ◽  
Power Law Creep

Uniaxial and multiaxial forms of a constitutive equation, characterizing the creep-damaging behavior of metals at elevated temperatures, are developed based on Dyson’s constrained cavity growth mechanism. The model employs a single scalar internal variable which can be identified with the area fraction of cavitated boundaries. This variable, together with the power law creep model is capable of describing steady creep, tertiary creep, and dilatation arising from the nucleation and growth of grain boundary cavities.

scholarly journals Анализ механизмов уплотнения термоэлектрических порошков скуттерудитов и сплавов Гейслера в процессе активированного полем спекания

2021 ◽  
Vol 55 (12) ◽  
pp. 1132
Author(s):  
А.С. Тукмакова ◽  
Н.И. Хахилев ◽  
Д.Б. Щеглова ◽  
В.Д. Насонов ◽  
А.П. Новицкий ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Heusler Alloys ◽  
Rate Sensitivity ◽  
Grain Boundary Sliding ◽  
Creep Mechanism ◽  
Diffusional Creep ◽  
Creep Model ◽  
Ceramic Powders ◽  
Boundary Sliding ◽  
Power Law Creep

The analysis of the shrinkage rate of powders, based on the power-law creep model of a porous body, was carried out in this paper to calculate the compaction parameters of CoSb3-based skutterudites and Fe2VAl-based Heusler alloys within field-activated sintering. It was indicated that this method, which had already been used for metal and ceramic powders, is applicable for thermoelectric powders. The values of strain rate sensitivity were obtained, and the corresponding powder compaction mechanisms have been defined. The main creep mechanism for skutterudites was found to be a dislocation climb, that later was replaced by grain boundary sliding, and the last sintering stage was associated with diffusional creep. The main creep mechanism for Heusler alloys was grain boundary sliding, later replaced by diffusional creep.

Interface Structure and Slip Transmission in TI-49AL-3NB

1991 ◽  
Vol 229 ◽  
Author(s):  
Daniel S. Schwartz ◽  
S. M. L. Sastry
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Interphase Boundary ◽  
Elevated Temperatures ◽  
Interface Structure ◽  
Nucleation And Growth ◽  
Slip Bands ◽  
Α Phase ◽  
Slip Transmission

AbstractTwo types of special grain boundaries were examined in Ti-49Al-3Nb deformed at elevated temperatures. The first can be described as a Σ=2 order-changing boundary. This boundary is faceted and results from the nucleation and growth of variants of the γ phase from the parent α phase. The second type of grain boundary is a γ/α2 interphase boundary, and transmission of slip through this type of boundary was examined. Slip transmission from γ into α2 did not produce distinct slip bands in α2,. Slip transmission from γ through α2, and into the next γ lamella was possible even when the next γ lamella was in an orientation rotated relative to the first γ lamella.

scholarly journals Modelling the transition from grain-boundary sliding to power-law creep in dry snow densification

2021 ◽  
pp. 1-14
Author(s):  
Elizabeth M. Morris ◽  
Lynn N. Montgomery ◽  
Robert Mulvaney
Keyword(s):  
Grain Boundary ◽  
Transition Zone ◽  
Power Law ◽  
Transition Density ◽  
Grain Boundary Sliding ◽  
Smooth Transition ◽  
Physically Based ◽  
Boundary Sliding ◽  
Power Law Creep ◽  
Stage 1

Abstract This paper presents a physics-based macroscale model for the densification of dry snow which provides for a smooth transition between densification by grain-boundary sliding (stage 1) and densification by power-law creep (stage 2). The model uses established values of the stage 1 and 2 densification rates away from the transition zone and two transition parameters with a simple physical basis: the transition density and the half-width of the transition zone. It has been calibrated using density profiles from the SUMup database and physically based expressions for the transition parameters have been derived. The transition model produces better predictions of the depth of the nominal bubble close-off horizon than the Herron and Langway model, both in its classical form and in a recent version with re-optimised densification rates.

Observations oh Nucleation and Growth of Voids in Nickel

1970 ◽  
Vol 28 ◽  
pp. 414-415
Author(s):  
J. L. Brimhall ◽  
H. E. Kissinger ◽  
B. Mastel
Keyword(s):  
High Purity ◽  
Growth Stage ◽  
Elevated Temperatures ◽  
Early Growth ◽  
Nucleation And Growth ◽  
Pure Nickel ◽  
Different Temperatures ◽  
Total Fluence ◽  
Neutron Exposure ◽  
Growth Of Voids

Some information on the size and density of voids that develop in several high purity metals and alloys during irradiation with neutrons at elevated temperatures has been reported as a function of irradiation parameters. An area of particular interest is the nucleation and early growth stage of voids. It is the purpose of this paper to describe the microstructure in high purity nickel after irradiation to a very low but constant neutron exposure at three different temperatures.Annealed specimens of 99-997% pure nickel in the form of foils 75μ thick were irradiated in a capsule to a total fluence of 2.2 × 1019 n/cm2 (E > 1.0 MeV). The capsule consisted of three temperature zones maintained by heaters and monitored by thermocouples at 350, 400, and 450°C, respectively. The temperature was automatically dropped to 60°C while the reactor was down.

Spherulite Structures in a Melt Spun Fe-Ni Austenitic Steel

1985 ◽  
Vol 43 ◽  
pp. 52-53
Author(s):  
G. M. Michal ◽  
T. K. Glasgow ◽  
T. J. Moore
Keyword(s):  
Austenitic Steel ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Large Range ◽  
Amorphous Structure ◽  
Nucleation And Growth ◽  
Ni Alloys ◽  
Melt Spun ◽  
Crystal Fibers ◽  
Rapidly Solidified

Large additions of B to Fe-Ni alloys can lead to the formation of an amorphous structure, if the alloy is rapidly cooled from the liquid state to room temperature. Isothermal aging of such structures at elevated temperatures causes crystallization to occur. Commonly such crystallization pro ceeds by the nucleation and growth of spherulites which are spherical crystalline bodies of radiating crystal fibers. Spherulite features were found in the present study in a rapidly solidified alloy that was fully crysstalline as-cast. This alloy was part of a program to develop an austenitic steel for elevated temperature applications by strengthening it with TiB2. The alloy contained a relatively large percentage of B, not to induce an amorphous structure, but only as a consequence of trying to obtain a large volume fracture of TiB2 in the completely processed alloy. The observation of spherulitic features in this alloy is described herein. Utilization of the large range of useful magnifications obtainable in a modern TEM, when a suitably thinned foil is available, was a key element in this analysis.

Inhomogeneous Swelling Near Grain Boundaries in Irradiated Materials: Cavity Nucleation and Growth Saturation Effects

2000 ◽  
Vol 650 ◽  
Author(s):  
S. L. Dudarev
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Nucleation And Growth ◽  
Homogeneous Distribution ◽  
Rate Theory ◽  
Diffusional Growth ◽  
Standard Rate ◽  
Saturation Effects ◽  
Kinetics Of ◽  
Cascade Damage

ABSTRACTThe effect of inhomogeneous nucleation and growth of cavities near grain boundaries illustrates the failure of the standard rate theory to describe the kinetics of phase transformations in irradiated materials under cascade damage conditions. The enhanced swelling observed near grain boundaries is believed to result from the competition between the diffusional growth of cavities and their shrinkage due to the interaction with mobile interstitial clusters. Swelling rates associated with the two processes behave in a radically different way as a function of the size of growing cavities. For a spatially homogeneous distribution of cavities this gives rise to the saturation of swelling in the limit of large irradiation doses.We investigate the evolution of the population of cavities nucleating and growing near a planar grain boundary. We show that a cavity growing near the boundary is able to reach a size that is substantially larger than the size of a cavity growing in the interior region of the grain. For a planar grain boundary the magnitude of swelling at maximum is found to be up to eight times higher than the magnitude of swelling in the grain interior.

Grain-boundary cavity growth during high-temperature creep and fatigue

Metal Science ◽  
1981 ◽  
Vol 15 (2) ◽  
pp. 73-78 ◽  
Author(s):  
K. U. Snowden ◽  
D. S. Hughes ◽  
P. A. Stathers
Keyword(s):  
High Temperature ◽  
Grain Boundary ◽  
Cavity Growth ◽  
High Temperature Creep ◽  
Temperature Creep

Creep Simulation of the Hydroprocessing Reactor Using a Physically-Based CDM Model

2015 ◽  
Author(s):  
Yu Zhou ◽  
Chen Xuedong ◽  
Fan Zhichao ◽  
Jie Dong
Keyword(s):  
Damage Mechanics ◽  
Failure Modes ◽  
Elevated Temperatures ◽  
Three Dimensional ◽  
Critical Issue ◽  
Fe Modelling ◽  
Creep Failure ◽  
Good Tool ◽  
Element Analysis ◽  
Physically Based

Creep failure is one of the most important failure modes in the design of hydroprocessing reactors at elevated temperatures, and the accurate prediction of the creep behavior in structural discontinuities is a critical issue for component design. A physically-based continnum damage mechanics (CDM) model was adopted to describe all three creep stages of 2.25Cr-1Mo-0.25V ferritic steel widely used in manufacturing modern hydroprocessing reactors. The material constants in the damage constitutive equations were identified using an efficient optimization scheme based on genetic algorithm (GA). The user-defined subroutine implementing the CDM model was developed using user programmable features (UPFs) in ANSYS. Three-dimensional finite element analysis of the hydroprocessing reactor was conducted to determine the critical regions, and the studies on the stress redistribution and the prediction of damage evolution in these regions during creep were carried out. The results show that FE modelling based on CDM theory can provide a good tool for creep design of complex engineering components.

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