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.

SEM Study of the Influence of Microstructure on Low Cycle Fatigue Crack Growth in Martensitic Steel I

2018 ◽  
Vol 774 ◽  
pp. 96-100 ◽  
Author(s):  
Tamaz Eterashvili ◽  
Temur Dzigrashvili ◽  
M. Vardosanidze
Keyword(s):  
Room Temperature ◽  
Martensitic Steel ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Cycle Fatigue ◽  
Slip Bands ◽  
Sem Study ◽  
Austenite Grains ◽  
Plastic Zones ◽  
The Impact

Distribution of fatigue cracks in chromium martensitic steel after low cycle fatigue (LCF) tests at room temperature has been studied using SEM, and the experimental evidences of localized plastic flow (LPF) are presented. The influence of the location of LPF and the microstructure elements on the trajectory and growth of microcracks is also considered. The dimensions of plastic zones ahead of macrocrack tip as well as at its edges were measured in the process of crack propagation inside of the sample. The processes occurring in plastic zone, particularly ahead of macrocrack tip, were analyzed. Distribution, orientation and the reasons of slip bands’ formation as well as the microstructure elements at which they were nucleated have been studied. The impact of the slip bands’ orientation on the process of macrocrack growth was also analyzed. In addition the interactions of a crack with the boundaries of former austenite grains, martensitic packets, martensitic laths, slip bands and precipitates have been discussed.

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.

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.

Formation of Persistent Slip Band in Fatigued Copper Single Crystals

1982 ◽  
Vol 40 ◽  
pp. 470-471
Author(s):  
N. Y. Jin
Keyword(s):  
Volume Fraction ◽  
Fatigue Cracks ◽  
Wall Structure ◽  
Matrix Structure ◽  
Dislocation Dipole ◽  
Slip Bands ◽  
Persistent Slip Bands ◽  
The Matrix ◽  
Hard Shell ◽  
Copper Single Crystals

Localised plastic deformation in Persistent Slip Bands(PSBs) is a characteristic feature of fatigue in many materials. The dislocation structure in the PSBs contains regularly spaced dislocation dipole walls occupying a volume fraction of around 10%. The remainder of the specimen, the inactive "matrix", contains dislocation veins at a volume fraction of 50% or more. Walls and veins are both separated by regions in which the dislocation density is lower by some orders of magnitude. Since the PSBs offer favorable sites for the initiation of fatigue cracks, the formation of the PSB wall structure is of great interest. Winter has proposed that PSBs form as the result of a transformation of the matrix structure to a regular wall structure, and that the instability occurs among the broad dipoles near the center of a vein rather than in the hard shell surounding the vein as argued by Kulmann-Wilsdorf.

Low-Cycle Fatigue Performance of Buckling Restrained Braces and Assessment of Cumulative Damage under Severe Earthquakes

2018 ◽  
Vol 763 ◽  
pp. 867-874
Author(s):  
Yu Shu Liu ◽  
Ke Peng Chen ◽  
Guo Qiang Li ◽  
Fei Fei Sun
Keyword(s):  
Fatigue Life ◽  
Energy Dissipation ◽  
Structural Reliability ◽  
Low Cycle Fatigue ◽  
Engineering Application ◽  
Fatigue Performance ◽  
Cycle Fatigue ◽  
Variable Amplitude ◽  
Buckling Restrained Braces ◽  
Energy Dissipation Devices

Buckling Restrained Braces (BRBs) are effective energy dissipation devices. The key advantages of BRB are its comparable tensile and compressive behavior and stable energy dissipation capacity. In this paper, low-cycle fatigue performance of domestic BRBs is obtained based on collected experimental data under constant and variable amplitude loadings. The results show that the relationship between fatigue life and strain amplitude satisfies the Mason-Coffin equation. By adopting theory of structural reliability, this paper presents several allowable fatigue life curves with different confidential levels. Besides, Palmgren-Miner method was used for calculating BRB cumulative damages. An allowable damage factor with 95% confidential level is put forward for assessing damage under variable amplitude fatigue. In addition, this paper presents an empirical criterion with rain flow algorithm, which may be used to predict the fracture of BRBs under severe earthquakes and provide theory and method for their engineering application. Finally, the conclusions of the paper were vilified through precise yet conservative prediction of the fatigue failure of BRB.

Low-Cycle Fatigue Behaviour of Gas Turbine Alloys

1974 ◽  
Vol 188 (1) ◽  
pp. 321-328 ◽  
Author(s):  
W. J. Evans ◽  
G. P. Tilly
Keyword(s):  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
High Stress ◽  
Cyclic Creep ◽  
Fatigue Curve ◽  
Fatigue Behaviour ◽  
Material Surface ◽  
Tension Stress ◽  
Cycle Fatigue ◽  
Stress Tests

The low-cycle fatigue characteristics of an 11 per cent chromium steel, two nickel alloys and two titanium alloys have been studied in the range 20° to 500°C. For repeated-tension stress tests on all the materials, there was a sharp break in the stress-endurance curve between 103 and 104 cycles. The high stress failures were attributed to cyclic creep contributing to the development of internal cavities. At lower stresses, failures occurred through the growth of fatigue cracks initiated at the material surface. The whole fatigue curve could be represented by an expression developed from linear damage assumptions. Data for different temperatures and types of stress concentration were correlated by expressing stress as a fraction of the static strength. Repeated-tensile strain cycling data were represented on a stress-endurance diagram and it was shown that they correlated with push-pull stress cycles at high stresses and repeated-tension at low stresses. In general, the compressive phase tended to accentuate cyclic creep so that ductile failures occurred at proportionally lower stresses. Changes in frequency from 1 to 100 cycle/min were shown to have no significant effect on low-cycle fatigue behaviour.

Plastic Slip and Early Stage of Fatigue Damage in Polycrystals: Comparison between Experiments and Crystal Plasticity Finite Elements Simulations

2014 ◽  
Vol 891-892 ◽  
pp. 1711-1716 ◽  
Author(s):  
Loic Signor ◽  
Emmanuel Lacoste ◽  
Patrick Villechaise ◽  
Thomas Ghidossi ◽  
Stephan Courtin
Keyword(s):  
Fatigue Crack ◽  
Finite Elements ◽  
Crack Initiation ◽  
Fatigue Damage ◽  
Crystal Plasticity ◽  
Early Stage ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Plastic Slip

For conventional materials with solid solution, fatigue damage is often related to microplasticity and is largely sensitive to microstructure at different scales concerning dislocations, grains and textures. The present study focuses on slip bands activity and fatigue crack initiation with special attention on the influence of the size, the morphology and the crystal orientation of grains and their neighbours. The local configurations which favour - or prevent - crack initiation are not completely identified. In this work, the identification and the analysis of several crack initiation sites are performed using Scanning Electron Microscopy and Electron Back-Scattered Diffraction. Crystal plasticity finite elements simulation is employed to evaluate local microplasticity at the scale of the grains. One of the originality of this work is the creation of 3D meshes of polycrystalline aggregates corresponding to zones where fatigue cracks have been observed. 3D data obtained by serial-sectioning are used to reconstruct actual microstructure. The role of the plastic slip activity as a driving force for fatigue crack initiation is discussed according to the comparison between experimental observations and simulations. The approach is applied to 316L type austenitic stainless steels under low-cycle fatigue loading.

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