Modelling of Low Cycle Fatigue Initiation of 316LN Based on Crystalline Plasticity and Geometrically Necessary Dislocations

2010 ◽  
Vol 636-637 ◽  
pp. 1137-1142 ◽  
Author(s):  
Julien Schwartz ◽  
Olivier Fandeur ◽  
Colette Rey
Keyword(s):  
Lattice Structure ◽  
Low Cycle Fatigue ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Lattice Curvature ◽  
Crystalline Plasticity ◽  
Numerical Studies ◽  
Slip Bands ◽  
Persistent Slip Bands ◽  
Number Of Cycles

Initiation of intragranular cracks during low cycle fatigue is governed by complex microstructural phenomena. Depending on the loading amplitude, number of cycles, lattice structure and/or chemical composition, different dislocation structures (veins, cells or Persistent Slip Bands) develop and induce heterogeneous localization of strain and stress in the material. For a better comprehension of crack initiation in 316LN stainless steel, low cycle fatigue tests and numerical simulations were performed. Specimens of 316LN steel with polished shallow notch were cycled with constant loading amplitude and Persistant Slip Bands were identified by SEM observations. In parallel, numerical studies were carried out with the model of cristalline plasticity CristalECP. Simulations were performed on 3D polycristalline aggregates of 316LN steel with the finite elements code Abaqus® and Cast3m®. The results show a heterogeneous localization of strain in bands. For a more precise computation of the mechanical fields and to introdruce a grain size effect, Geometrically Necessary Dislocations were introduced in CristalECP. The GNDs are directly related and computed with the lattice curvature.

Structure Changes in Stainless Steels Used in Nuclear Reactors and Turbo Generators after Minor Low Cycle Fatigue Deformation

2005 ◽  
Vol 475-479 ◽  
pp. 3505-3508
Author(s):  
Tamaz Eterashvili ◽  
T. Dzigrashvili ◽  
M. Vardosanidze
Keyword(s):  
Room Temperature ◽  
Nuclear Reactors ◽  
Low Cycle Fatigue ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Slip Bands ◽  
Structure Changes ◽  
Before And After ◽  
Number Of Cycles ◽  
Local Plastic Deformation

The structure of austenitic steel before and after 25% of total number of cycles of low cycle fatigue tests conducted at room temperature is studied using TEM. It is shown that the cyclic deformation of the steel proceeds heterogeneously. The microstructure of the steel is investigated in the area between the deformed and undistorted parts of the samples. The crystallography of the observed twins and the slip bands is specified. The value of local plastic deformation within a micro area of a grain is measured, and the influence of microstructure on crack initiation is discussed.

Initial Aspects of Low-Cycle Fatigue Fracture of Martensitic Steels

2007 ◽  
Vol 348-349 ◽  
pp. 385-388 ◽  
Author(s):  
Tamaz Eterashvili ◽  
T. Dzigrashvili ◽  
M. Vardosanidze
Keyword(s):  
Plastic Deformation ◽  
Stainless Steel ◽  
Plastic Zone ◽  
Fatigue Fracture ◽  
Main Crack ◽  
Low Cycle Fatigue ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Slip Bands ◽  
Number Of Cycles

This study deals with the SEM and optical microscopic characterization of fatigue plastic deformation process during fatigue crack initiation to understand where, why and how cracks initiate under conditions of low cycle fatigue. Samples were prepared from the 13Х11Н2В2МФ high-chromium stainless steel used for fusion power applications. The low-cycle tests were conducted at room temperature with the standard V-notched samples prepared from conventional stainless steel. The following characteristics were studied during fatigue tests: 1 macrocrack propagation, 2. interaction between macrocrack and isolated microcracks, 3. interaction between macrocrack and slip bands, 4. interaction between macrocrack and microstructure elements of the steel. The above experiments show that during macrocrack propagation a plastic zone is formed around it, where isolated microcracks and slip bands of 2-3 different directions are observed. Measurement of plastic zone dimensions after different number of cycles of deformation show that plastic zone size increases during the first stage of cyclic deformation (until definite number of cycles are completed), and then remains unchanged. The observations show that main crack is composed of individual micro-components, the lengths of which are in a good correlation with the dimensions of microstructure elements of the steel (former austenite grains, martensite crystals). It was revealed that during growth, as a rule, macrocrack rarely propagates along isolated microcracks and slip bands. Direction of macrocrack propagation changes while passing from one microstructure element to another, so that main direction is the same. No preferable transcrystalline or intercrystalline propagation of macrocrack has been observed in the investigated steel. It is shown that after subsequent fatigue tests, dimensions of the previously created slip bands increase, and additional new slip band are also formed. The sites and frequency of slip bands’ formation in plastic zone are also studied. It was observed that the boundaries and mainly the sites of intersection of martensite crystals are the sites of isolated (rough) microcracks’ formation. The dimensions of slip bands are comparable with those of martensite crystals. The angles between the main crack propagation direction and slip bands varied from 30o to 60o, however, most of the slip bands were oriented at 45o to the main crack. Based on the obtained results a conclusion is made that plastic deformation in samples go inhomogeneously. In plastic zones, along with the heavily deformed areas, almost non-deformed areas are also observed. The speed of fatigue fracture increases with the increase in frequency and amplitude of deformations. Generally, the annealed samples are destructed prematurely in comparison with non-annealed ones of the investigated steel.

Structure Changes in Stainless Steels Used in Nuclear Reactors and Turbo Generators after Minor Low Cycle Fatigue Deformation

2005 ◽  
Vol 475-479 ◽  
pp. 1487-1490 ◽  
Author(s):  
Tamaz Eterashvili ◽  
T. Dzigrashvili ◽  
M. Vardosanidze
Keyword(s):  
Room Temperature ◽  
Nuclear Reactors ◽  
Low Cycle Fatigue ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Slip Bands ◽  
Structure Changes ◽  
Before And After ◽  
Number Of Cycles ◽  
Local Plastic Deformation

The structure of austenitic steel before and after 25% of total number of cycles of low cycle fatigue tests conducted at room temperature is studied using TEM. It is shown that the cyclic deformation of the steel proceeds heterogeneously. The microstructure of the steel is investigated in the area between the deformed and undistorted parts of the samples. The crystallography of the observed twins and the slip bands is specified. The value of local plastic deformation within a micro area of a grain is measured, and the influence of microstructure on crack initiation is discussed.

Low Cycle Fatigue Tests and Simulations on Steel Elbows

2013 ◽  
Author(s):  
Patricia Pappa ◽  
George E. Varelis ◽  
Spyros A. Karamanos ◽  
Arnold M. Gresnigt
Keyword(s):  
Finite Element ◽  
Low Cycle Fatigue ◽  
Local Strain ◽  
Fatigue Behaviour ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Out Of Plane ◽  
Strain Gauge Measurements ◽  
Number Of Cycles

In this paper the low cycle fatigue behaviour of steel elbows under strong cyclic loading conditions (in-plane and out-of-plane) is examined. The investigation is conducted through advanced finite element analysis tools, supported by real-scale test data for in-plane bending. The numerical results are successfully compared with the experimental measurements. In addition, a parametric study is conducted, which is aimed at investigating the effects of the diameter-to-thickness ratio on the low-cycle fatigue of elbows, focusing on the stress and strain variations. Strain gauge measurements are compared with finite element models. Upon calculation of local strain variation at the critical location, the number of cycles to fracture can be estimated.

Evaluation of Low-Cycle Fatigue in Simulated PWR Environment

2006 ◽  
Vol 326-328 ◽  
pp. 1011-1014 ◽  
Author(s):  
Ill Seok Jeong ◽  
Sang Jai Kim ◽  
Taek Ho Song ◽  
Sung Yull Hong
Keyword(s):  
Fatigue Life ◽  
Nuclear Power ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Water Environment ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Fatigue Design ◽  
Number Of Cycles ◽  
Measured Length

For developing fatigue design curve of cast stainless steel that is used in piping material of nuclear power plants, a low-cycle fatigue test rig was built. It is capable of performing tests in pressurized high temperature water environment of PWR. Cylindrical solid fatigue specimens of CF8M were used for the strain-controlled environmental fatigue tests. Fatigue life was measured in terms of the number of cycles with the variation of strain amplitude at 0.04%/s strain rates. The disparity between target length and measured length of specimens was corrected by using finite element method. The corrected test results showed similar fatigue life trend with other previous results.

Low Cycle Fatigue Behaviour of GX12CrMoVNbN9 -1 Cast Steel at Room Temperature

2011 ◽  
Vol 291-294 ◽  
pp. 1106-1109 ◽  
Author(s):  
Grzegorz Golański ◽  
Krzysztof Werner ◽  
Stanisław Mroziński
Keyword(s):  
Heat Treatment ◽  
Room Temperature ◽  
Low Cycle Fatigue ◽  
Cast Steel ◽  
Fatigue Behaviour ◽  
Fatigue Tests ◽  
Total Strain Amplitude ◽  
Cycle Fatigue ◽  
Number Of Cycles ◽  
Stabilization Period

The report treats of the low cycle fatigue (LCF) behaviour of GX12CrMoVNbN9-1 (GP91) cast steel after heat treatment (1040°C/12h/oil + 760°C/12h/air + 750°C/8h/furnace). Fatigue tests were carried out at room temperature for five levels of the controlled total strain amplitude εac = 0.25, 0.30, 0.35, 0.50 and 0.60 %. The research performed within the scope of LCF has shown in general that the investigated cast steel was subject to strong cyclic weakening, revealing no stabilization period at the same time. At the final stage of fatigue there was quick weakening of the material which proceeded till its destruction. The growth of amplitude εac resulted in reducing the number of cycles till the destruction stage.

An Experimental Study on Low Cycle Fatigue of Inconel 617 Super Alloy

2006 ◽  
Vol 306-308 ◽  
pp. 163-168 ◽  
Author(s):  
Jae Hoon Kim ◽  
Duck Hoi Kim ◽  
Young Shin Lee ◽  
Young Jin Choi ◽  
Hyun Soo Kim ◽  
...  
Keyword(s):  
Strain Energy ◽  
Low Cycle Fatigue ◽  
Cyclic Hardening ◽  
Fatigue Tests ◽  
Cyclic Behavior ◽  
Cycle Fatigue ◽  
Inconel 617 ◽  
Number Of Cycles ◽  
Cycles To Failure ◽  
Super Alloy

Low cycle fatigue tests are performed on the Inconel 617 super alloy that be used for structural material of hot gas casing for gas turbine. The relations between strain energy density and number of cycles to failure are examined in order to predict the low cycle fatigue life of Inconel 617 super alloy. The lives predicted by strain energy methods are found to coincide with experimental data and results obtained from the Coffin-Manson method. And, the cyclic behavior of the Inconel 617 super alloy is characterized by cyclic hardening with increasing number of cycles.

About Fatigue Tests End Criterion in Elevated Temperatures

2014 ◽  
Vol 598 ◽  
pp. 153-159 ◽  
Author(s):  
Stanisław Mroziński ◽  
Michał Piotrowski
Keyword(s):  
Elevated Temperature ◽  
Experimental Verification ◽  
Elevated Temperatures ◽  
Low Cycle Fatigue ◽  
Analytical Description ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Quantitative Criterion ◽  
Metal Materials ◽  
Number Of Cycles

In this paper there has been presented a new quantitative criterion of the end of a low-cycle fatigue test conducted in the conditions of fixed amplitude loads. In this criterion there is used an analytical description of the parameters of the hysteresis loop and the number of cycles till the fracture. The conducted experimental verification of this criterion enabled to obtain satisfactory results. In the paper it has been stated that the presented criterion can have a special application in the case of tests of metal materials in an elevated temperature.

scholarly journals Investigating the Interaction between Persistent Slip Bands and Surface Hard Coatings via Crystal Plasticity Simulations

Crystals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1012
Author(s):  
Mohammad S. Dodaran ◽  
Jian Wang ◽  
Nima Shamsaei ◽  
Shuai Shao
Keyword(s):  
Crystal Plasticity ◽  
Coating Thickness ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Hard Coatings ◽  
Fatigue Performance ◽  
Shear Stresses ◽  
Cycle Fatigue ◽  
Slip Bands ◽  
Persistent Slip Bands

Fatigue cracks often initiate from the surface extrusion/intrusions formed due to the operation of persistent slip bands (PSBs). Suppression of these surface topographical features by hard surface coatings can significantly extend fatigue lives under lower stress amplitudes (i.e., high cycle fatigue), while cracks initiate early in the coating or in the coating–substrate interface under higher stress amplitudes (i.e., low cycle fatigue), deteriorating the fatigue performance. However, both beneficial and detrimental effects of the coatings appear to be affected by the coating–substrate material combination and coating thickness. A quantitative understanding of the role of these factors in the fatigue performance of materials is still lacking. In this study, crystal plasticity simulations were employed to elucidate the dependence of the coating’s effects on two factors—i.e., the coating thickness and loading amplitudes. The results revealed that the thicker coatings more effectively suppress the operation of the PSBs, but generate higher tensile and shear stresses, normal and parallel to the interfaces, respectively, promoting interfacial delamination. The tensile stresses parallel to the interface within the coating, which favors coating fracture, are not sensitive to the coating thickness.

TEM Study of Microstructure Changes, Formation and Distribution of Slip Bands in Austenitic Steels after Low-Cycle Fatigue (LCF) Deformation - II

2015 ◽  
Vol 665 ◽  
pp. 141-144
Author(s):  
Tamaz Eterashvili ◽  
T. Dzigrashvili ◽  
M. Vardosanidze
Keyword(s):  
Plastic Deformation ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Austenitic Steels ◽  
Cycle Fatigue ◽  
Localized Deformation ◽  
Microstructure Changes ◽  
Slip Bands ◽  
Micro Deformation ◽  
Number Of Cycles

The microstructure changes, development of micro plastic deformation and formation and distribution of slip bands were studied. It is shown that development of micro deformation during LCF depends on loading conditions (amplitude and number of cycles) and microstructureIt is shown that as non-localized as well as localized micro plastic deformation takes place because of structural inhomogeneity. Supposedly, the localized deformation is related to the sites of internal stress concentration accumulated during the LCF.The effect of microstructure of structural steels on the rate of local cyclic deformation, leading to nucleation and growth of slip bands of fatigue cracks, was studied. The interaction of slip bands with precipitates, grain boundaries and low-angle boundaries were also analyzed.The sites of nucleation of primary and secondary slip bands were identified, and the following aspects were considered: 1. the possibility of microcrack nucleation on (or in) slip bands, 2. The kind of slip bands the slip bands may nucleate in, 3. The potential sites (except the slip bands) and reasons of nanocrack formation are specified.

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