Fatigue damage of ultrafine-grain copper in very-high cycle fatigue region

2011 ◽  
Vol 528 (22-23) ◽  
pp. 7036-7040 ◽  
Author(s):  
P. Lukáš ◽  
L. Kunz ◽  
L. Navrátilová ◽  
O. Bokůvka
Keyword(s):  
Fatigue Damage ◽  
High Cycle Fatigue ◽  
Ultrafine Grain ◽  
Cycle Fatigue ◽  
Very High Cycle Fatigue ◽  
Very High

The Influence of Microstructure Heterogeneities on the Very High Cycle Fatigue Behavior of Duplex Stainless Steel

2016 ◽  
Vol 258 ◽  
pp. 255-258
Author(s):  
Ulrich Krupp ◽  
Marcus Söker ◽  
Tina Waurischk ◽  
Alexander Giertler ◽  
Benjamin Dönges ◽  
...  
Keyword(s):  
Fatigue Damage ◽  
High Cycle Fatigue ◽  
Fatigue Behavior ◽  
Ion Beam ◽  
Cyclic Plasticity ◽  
Cycle Fatigue ◽  
Heterogeneous Distribution ◽  
Very High Cycle Fatigue ◽  
Structural Applications ◽  
Very High

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.

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

2014 ◽  
Vol 783-786 ◽  
pp. 2266-2271 ◽  
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.

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

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.

scholarly journals Usability of Ultrasonic Frequency Testing for Rapid Generation of High and Very High Cycle Fatigue Data

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2245
Author(s):  
Michael Fitzka ◽  
Bernd M. Schönbauer ◽  
Robert K. Rhein ◽  
Niloofar Sanaei ◽  
Shahab Zekriardehani ◽  
...  
Keyword(s):  
Strain Rate ◽  
High Cycle Fatigue ◽  
Fatigue Properties ◽  
Ultrasonic Frequency ◽  
Cycle Fatigue ◽  
Reinforced Polymer ◽  
Very High Cycle Fatigue ◽  
Ultrasonic Fatigue ◽  
Fibre Reinforced Polymer ◽  
Very High

Ultrasonic fatigue testing is an increasingly used method to study the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) properties of materials. Specimens are cycled at an ultrasonic frequency, which leads to a drastic reduction of testing times. This work focused on summarising the current understanding, based on literature data and original work, whether and how fatigue properties measured with ultrasonic and conventional equipment are comparable. Aluminium alloys are not strain-rate sensitive. A weaker influence of air humidity at ultrasonic frequencies may lead to prolonged lifetimes in some alloys, and tests in high humidity or distilled water can better approximate environmental conditions at low frequencies. High-strength steels are insensitive to the cycling frequency. Strain rate sensitivity of ferrite causes prolonged lifetimes in those steels that show crack initiation in the ferritic phase. Austenitic stainless steels are less prone to frequency effects. Fatigue properties of titanium alloys and nickel alloys are insensitive to testing frequency. Limited data for magnesium alloys and graphite suggest no frequency influence. Ultrasonic fatigue tests of a glass fibre-reinforced polymer delivered comparable lifetimes to servo-hydraulic tests, suggesting that high-frequency testing is, in principle, applicable to fibre-reinforced polymer composites. The use of equipment with closed-loop control of vibration amplitude and resonance frequency is strongly advised since this guarantees high accuracy and reproducibility of ultrasonic tests. Pulsed loading and appropriate cooling serve to avoid specimen heating.

scholarly journals On the determination of the bending fatigue strength in and above the very high cycle fatigue regime of shot-peened gears

2021 ◽  
Author(s):  
D. Fuchs ◽  
S. Schurer ◽  
T. Tobie ◽  
K. Stahl
Keyword(s):  
Fatigue Strength ◽  
High Cycle Fatigue ◽  
Load Carrying Capacity ◽  
Cycle Fatigue ◽  
Bending Fatigue ◽  
Very High Cycle Fatigue ◽  
Bending Load ◽  
Load Carrying ◽  
Bending Fatigue Strength ◽  
Very High

AbstractDemands on modern gearboxes are constantly increasing, for example to comply with lightweight design goals or new CO2 thresholds. Normally, to increase performance requires making gearboxes and powertrains more robust. However, this increases the weight of a standard gearbox. The two trends therefore seem contradictory. To satisfy both of these goals, gears in gearboxes can be shot-peened to introduce high compressive residual stresses and improve their bending fatigue strength. To determine a gear’s tooth root bending fatigue strength, experiments are conducted up to a defined number of load cycles in the high cycle fatigue range. However, investigations of shot-peened gears have revealed tooth root fracture damage initiated at non-metallic inclusions in and above the very high cycle fatigue range. This means that a further reduction in bending load carrying capacity has to be expected at higher load cycles, something which is not covered under current standard testing conditions. The question is whether there is a significant decrease in the bending load carrying capacity and, also, if pulsating tests conducted at higher load cycles—or even tests on the FZG back-to-back test rig—are necessary to determine a proper endurance fatigue limit for shot-peened gears. This paper examines these questions.

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