A physically based fatigue damage model for simulating three-dimensional stress states in composites under very high cycle fatigue loading

As being used for structural applications, where a high corrosion resistance is required, the fatigue behavior of duplex stainless steels (DSS) is governed by the partition of cyclic plasticity to the two phases, ferrite and austenite, respectively. Under very high cycle fatigue (VHCF) loading conditions, the heterogeneous distribution of crystallographic misorientations between neighboring grains and phases yields to a pronounced scatter in fatigue life, ranging from 1 million to 1 billion cycles for nearly the same stress amplitude. In addition, the relevant damage mechanisms depend strongly on the atmosphere. Stress corrosion cracking in NaCl-containing atmosphere causes a pronounced decrease in the VHCF life. By means of ultrasonic fatigue testing at 20kHz in combination with high resolution scanning electron microscopy, electron back-scattered diffraction (EBSD), focused ion beam milling (FIB) and synchrotron tomography, the microstructure heterogeneities were quantified and correlated with local fatigue damage. It has been shown that the fatigue process is rather complex, involving redistribution of residual stresses and three-dimensional barrier effects of the various interfaces. The application of a 2D/3D finite element model allows a qualitative prediction of the fatigue-damage process in DSS that is controlled by stochastic local microstructure arrangements.

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PSBs and Non-Propagation of Small Surface and Interior Cracks in Polycrystalline Copper

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.592-593.777 ◽

2013 ◽

Vol 592-593 ◽

pp. 777-780 ◽

Cited By ~ 1

Author(s):

Stefanie E. Stanzl-Tschegg ◽

Bernd M. Schönbauer

Keyword(s):

High Cycle Fatigue ◽

Fatigue Loading ◽

Cycle Fatigue ◽

Lower Stress ◽

Small Surface ◽

Loading Method ◽

Very High Cycle Fatigue ◽

Small Cracks ◽

Number Of Cycles ◽

Very High

PSB formation and its relevance for an eventual fatigue limit of polycrystalline electrolytic copper was studied in the very-high cycle fatigue regime with the ultrasound fatigue loading method. PSBs are formed at much lower stress/strain amplitudes than reported in earlier literature, if a high enough number of cycles is applied. Fatigue fracture takes place at approximately 50% higher amplitudes than needed for PSB formation, which is likewise in contrast to former literature results. Non-propagation of small cracks, originating from intrusions or PSB-induced non-propagating grain-boundary cracks are made responsible for this different material response.

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Nonlinear dynamics and stages of damage of Ti6Al4V and Ti45Nb titanium alloys in very high cycle fatigue

PNRPU Mechanics Bulletin ◽

10.15593/perm.mech/2020.2.12 ◽

2020 ◽

pp. 145-153

Author(s):

M. V Bannikov ◽

V. A Oborin ◽

D. A Bilalov ◽

O. B Naimark

Keyword(s):

Titanium Alloys ◽

High Cycle Fatigue ◽

Three Dimensional ◽

Fatigue Properties ◽

Experimental Program ◽

Cycle Fatigue ◽

Very High Cycle Fatigue ◽

Number Of Cycles ◽

Radial Shear Rolling ◽

Very High

The paper presents an experimental methodology aimed at evaluating a very-high cycle resource for aviation titanium alloys Vt-6 (Ti6Al4V) and Ti45Nb for medical applications with different microstructures (large-crystal and submicrocrystalline ones). The submicrocrystalline (SMC) state was obtained by an intensive plastic deformation realized in two ways: the three-dimensional forging for Ti45Nb and radial-shear rolling for Ti6Al4V. The experimental program tests high-cycle and very-high-cycle loading (number of cycles 107-109) realized using the in situ determination method of the accumulation of the irreversible fatigue damage by analyzing nonlinear forms of feedback in a closed system ultrasonic fatigue setup. This makes it possible to establish the connection of the microscopic fatigue mechanisms with the model views and consider the stages of the damage development based on the nonlinear kinetics of the defect accumulation under cyclic loading in high- and gigacycle fatigue modes. We established various relations between changes in the amplitude of the second harmonic of vibrations of the free end of the samples with different internal structures, which are associated with the mechanisms of stress relaxation and damage accumulation. The grain size reduction in Ti45Nb alloy by the three-dimensional forging improved the fatigue properties by 1.3-1.5 times, whereas for VT-6 alloy, the radial-shear rolling method could not increase the fatigue properties in the very high cycle fatigue range, which may be caused by the presence of large residual internal stresses. Based on the scale parameters obtained earlier from the fracture surface morphology and the relations established in this work, the kinetic equations for the origin and growth of fatigue cracks in the gigacycle loading range will be constructed. This equation, based on the empirical power parameters related to the structure of the material, will allow us to determine the number of cycles for the origin of an internal crack and its growth to the surface.

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FE Modeling of FRP-Concrete Interface for very High Cycle Fatigue Behavior

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.577-578.165 ◽

2013 ◽

Vol 577-578 ◽

pp. 165-168 ◽

Cited By ~ 1

Author(s):

M. Mahal ◽

T. Blanksvärd ◽

B. Täljsten

Keyword(s):

Fatigue Damage ◽

High Cycle Fatigue ◽

Fatigue Behavior ◽

Three Dimensional ◽

Fatigue Loading ◽

Cycle Fatigue ◽

Finite Element Program ◽

Element Program ◽

Three Dimensional Finite Element ◽

Concrete Interface

The fatigue damage of FRP-concrete interface is a major problem in strengthened structures subjected to fatigue loading. The available FRP-concrete interface models published in the literature usually deal with fracture mechanism approach, which is unsuitable for high cycle fatigue damage. In this study, a constitutive micro model is developed for FRP-concrete interface for high cycle fatigue and incorporated into a three dimensional finite-element program. Numerical analysis of a double lap joint is carried out, and the results show that the proposed model is reasonably accurate.

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Microstructural Characterization of Fatigue Damage of CFRP in the Very High Cycle Fatigue Regime

Advanced Composites for Aerospace, Marine, and Land Applications II ◽

10.1007/978-3-319-48141-8_25 ◽

2015 ◽

pp. 325-334

Author(s):

Daniel Backe ◽

Frank Balle ◽

Dietmar Eifler

Keyword(s):

Fatigue Damage ◽

High Cycle Fatigue ◽

Microstructural Characterization ◽

Cycle Fatigue ◽

Very High Cycle Fatigue ◽

Very High

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On Fatigue Crack Initiation in the Matrix in Very High Cycle Fatigue Regime

Materials Science Forum ◽

10.4028/www.scientific.net/msf.783-786.2266 ◽

2014 ◽

Vol 783-786 ◽

pp. 2266-2271 ◽

Cited By ~ 1

Author(s):

Guo Cai Chai

Keyword(s):

Fatigue Crack ◽

Crack Initiation ◽

Fatigue Damage ◽

Strain Localization ◽

High Cycle Fatigue ◽

High Strain ◽

Fatigue Crack Initiation ◽

Cycle Fatigue ◽

Very High Cycle Fatigue ◽

Very High

In very high cycle fatigue, VHCF, regime, fatigue crack initiation can occur at subsurface defects such as inclusion or subsurface non-defect (matrix) origin. This paper provides a study on the fatigue crack initiation mechanisms at subsurface non-defect (matrix) origin in two metallic materials using electron backscatter diffraction and electron channeling contrast imaging. The results show that the strains in the material in the VHCF regime were highly localized, where the local maximum strain is greatly higher than the average strain value. This high strain localization can lead to the formation of fine grain zone and also fatigue damage or fatigue crack initiation at grain boundaries or twin boundaries by impingement cracking. High strain localization is caused by strain accumulation of each very small loading, and also increases the local hardness of the material. This may start quasi-cleavage crack origin, and consequently the formation of subsurface fatigue crack initiations. The results also show that fatigue damage and crack initiation mechanisms in the VHCF regime can be different in different metals due to the mechanisms for local plasticity exhaustion.

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Micro Mechanical Behaviors and Damage in Nickel Base Alloy and Steels during Very High Cycle Fatigue

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.258.506 ◽

2016 ◽

Vol 258 ◽

pp. 506-513

Author(s):

Guo Cai Chai

Keyword(s):

Fatigue Damage ◽

High Cycle Fatigue ◽

Base Alloy ◽

Fatigue Crack Initiation ◽

Cycle Fatigue ◽

Nickel Base Alloy ◽

Very High Cycle Fatigue ◽

Nickel Base ◽

Cyclic Plastic Deformation ◽

Very High

Fatigue damage in a metallic material during very high cycle fatigue can strongly be correlated to the microstructure. This paper provides a review and a discussion on the micro damage behaviors in a nickel base alloy and three steels during very high cycle fatigue using micro plasticity and material mechanics. The results show that cyclic plastic deformation in these materials can occur very locally even with an applied stress that is much lower than the yield strength. The fatigue damage occurs mainly at grain or twin boundaries due to local impingement and interaction of slip bands and these boundaries. The crystallographic properties, Schmid factors and orientations of grain and boundaries have very important roles to the fatigue damage. Subsurface fatigue crack initiation in the matrix is one of the mechanisms for very high cycle fatigue. In the fine granular area, high plastic strain localization and cyclic plastic deformation can lead to dislocation annihilation and consequently formation of vacancies, or eventually nanopores at the subcell boundary that leads to fatigue crack initiation and propagation.

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