scholarly journals Effect of Carburizing and Nitriding on Fatigue Properties of 18Cr2Ni4WA Steel in Very High Cycle Fatigue Regime

2021 ◽  
Vol 45 (3) ◽  
pp. 207-215
Author(s):  
Zhenduo Sun ◽  
Dongbo Hou ◽  
Wei Li
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
High Cycle Fatigue ◽  
Fatigue Properties ◽  
Cycle Fatigue ◽  
Internal Defect ◽  
Surface Fatigue ◽  
Very High Cycle Fatigue ◽  
The Relationship ◽  
Very High

The work aims to study the influence of carburizing and nitriding on fatigue properties of 18Cr2Ni4WA high strength steel in very high cycle fatigue regime. Very high cycle fatigue tests were carried out on 18Cr2Ni4WA Steel after carburizing and nitriding respectively. The micro morphology of fatigue fracture was observed by scanning electron microscope, the failure mode and failure mechanism were discussed. The relationship between fatigue life and defect size, FGA size, fish eye size of fracture was analyzed. The characteristic size of defects is evaluated by Gumbel, Weibull and GEV distribution functions, and a modified Akiniwa fatigue life prediction model considering the relationship between FGA size and inclusion size was established. The results showed that, nitriding and carburizing treatment improve the surface fatigue limit of the steel. The fatigue life decreases with the increase of internal defect size and FGA size. After carburizing and nitriding treatment, the internal fatigue strength of the specimen decreases slightly. When the failure probability is 99%, the internal defect sizes of nitrided specimens calculated by Weibull, Gumbel and GEV distributions are 141.5 μm, 148.4 μm and 211.7 μm respectively. The calculated internal defect sizes of carburized specimens are 47 μm, 67.8 μm and 40 μm respectively. Compared with the experimental data, the fatigue strength predicted by GEV is the most appropriate. carburizing and nitriding treatment can improve the surface fatigue strength of 18Cr2Ni4WA steel, but slightly reduce the internal fatigue strength. The prediction result of the new model is conservative when the failure probability is 99%, which is suitable for engineering application.

The Effects of Specimen Size on the Very High Cycle Fatigue Properties of FV520B-I

2015 ◽  
Author(s):  
Ming Zhang ◽  
Weiqiang Wang ◽  
Aiju Li
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
High Cycle Fatigue ◽  
Specimen Size ◽  
Fatigue Properties ◽  
Test Results ◽  
Cycle Fatigue ◽  
Very High Cycle Fatigue ◽  
Heat Effects ◽  
Very High

The authors researched the effects of specimen size on the very high cycle fatigue properties of FV520B-I through ultrasonic fatigue testing. The test results showed that the very high cycle fatigue mechanism was not changed and the fatigue properties declined as the specimen size increased. The S-N curve moved downward and the fatigue life decreased under the same stress level maybe due to the heat effects of large specimens in tests. The fatigue strength and the fatigue life were predicted by relevant models. The prediction of fatigue strength was close to test result, and the prediction of fatigue life was less effective compared with the previous prediction of small size specimen test results.

Evaluation of Very High Cycle Fatigue Properties of Low Temperature Nitrided Ti-6Al-4V Alloy Using Ultrasonic Testing Technology

2015 ◽  
Vol 664 ◽  
pp. 118-127 ◽  
Author(s):  
Shoichi Kikuchi ◽  
Stefan Heinz ◽  
Dietmar Eifler ◽  
Yuta Nakamura ◽  
Akira Ueno
Keyword(s):  
Fatigue Life ◽  
Low Temperature ◽  
Fatigue Fracture ◽  
Ultrasonic Testing ◽  
High Cycle Fatigue ◽  
Fatigue Properties ◽  
Ti Alloy ◽  
Cycle Fatigue ◽  
Very High Cycle Fatigue ◽  
Very High

Fatigue tests were carried out at the stress ratio R = -1 using a 20 kHz ultrasonic testing facility to investigate the effects of low temperature nitriding on the fatigue properties of Ti-6Al-4V alloy in the very high cycle fatigue (VHCF) regime in detail. The oscillation and fatigue behavior of the nitrided Ti-alloy were characterized by measuring parameters like the ultrasonic generator power, the displacement of the specimens and dissipated energy under ultrasonic cyclic load. Moreover, the surface microstructure of the nitrided Ti-alloy was characterized using a micro-Vickers hardness tester, an optical microscope, scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron backscatter diffraction technique (EBSD) to clarify the fatigue fracture mechanism. The Ti-alloy nitrided at the temperature of 873 K showed duplex S-N properties consisting of the respective fracture modes of the surface fracture and the subsurface fracture. The low temperature nitriding reduced the surface fatigue life of Ti-alloy in comparison to the un-nitrided one due to the formation of a brittle titanium nitride (Ti2N), whereas the subsurface fatigue life in the VHCF regime was increased by the low temperature nitriding. In addition, the fatigue fracture mechanisms of the low temperature nitrided Ti-alloy were discussed from viewpoints of fractography and fracture mechanics.

Super Long Life Fatigue Properties of Rail Steel U71Mn and U75V

2013 ◽  
Vol 690-693 ◽  
pp. 1753-1756
Author(s):  
Ze Fu Luo ◽  
Shi Ming Cui ◽  
Yan Zeng Wu ◽  
Qing Yuan Wang
Keyword(s):  
Fatigue Life ◽  
High Cycle Fatigue ◽  
Rail Steel ◽  
Fatigue Behavior ◽  
Test System ◽  
Railway Track ◽  
Fatigue Properties ◽  
Cycle Fatigue ◽  
Very High Cycle Fatigue ◽  
Very High

Railway track steel, U71Mn and U75V were fatigued in this study, with the help of ultrasonic fatigue test system, to investigate the high cycle fatigue life behaviors. The results showed that the fatigue damage still occurs when the fatigue life exceeds 107, and the evolution of S-N curve showed a ladder type. This test showed that the traditional view of fatigue design and life prediction method were unable to meet the requirements of machinery and equipment working in gigacycle fatigue range, very high cycle fatigue behavior of fatigue has become a major challenge for researchers. The scanning electron microscope analysis of crack initiation was performed to clarify the mechanism of very high cycle fatigue failure.

scholarly journals Defect induced cracking and modeling of fatigue strength for an additively manufactured Ti-6Al-4V alloy in very high cycle fatigue regime

2021 ◽  
Author(s):  
Weiqian Chi ◽  
Wenjing Wang ◽  
Chengqi Sun
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Crack Initiation ◽  
Surface Defect ◽  
High Cycle Fatigue ◽  
Projection Area ◽  
Cycle Fatigue ◽  
Very High Cycle Fatigue ◽  
Artificial Surface ◽  
Very High

Additively manufactured (AM) alloy usually inevitably contains defects during manufacturing processor in service. Defects, as a harmful factor, could significantly reduce the fatigue performance of materials. This paper shows that the location and introduced form of defects play an important role in high cycle and very high cycle fatigue (VHCF) behavior of selective laser melting Ti-6Al-4V alloy. The fatigue life descends linearly with stress amplitude for interior defect induced failure. While for artificial surface defect induced failure, the fatigue life descends at first, and then exhibits a plateau region feature. We also observed competition of interior crack initiation with fine granular area feature in VHCF regime. The paper indicates that only the size or the stress intensity factor range of the defect is not an appropriate parameter describing the effect of defect on the fatigue crack initiation. Finally, the effect of artificial surface defect on high cycle and VHCF strength is modeled, i.e. the fatigue strength  σ, fatigue life  N and defect size ( area)  (square root of projection area of defect perpendicular to principal stress direction) is expressed as  σ= CN( area) for  N0 and  σ= CN ( area) for  N≥N , where  C,  a and  n are constants, N  is the number of cycles at the knee point.

scholarly journals Stress Ratio and Notch Effects on the Very High Cycle Fatigue Properties of a Near-Alpha Titanium Alloy

Materials ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 1778 ◽  
Author(s):  
Kun Yang ◽  
Bin Zhong ◽  
Qi Huang ◽  
Chao He ◽  
Zhi-Yong Huang ◽  
...  
Keyword(s):  
Titanium Alloy ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Stress Ratio ◽  
High Cycle Fatigue ◽  
Stress Sensitivity ◽  
Mean Stress ◽  
Cycle Fatigue ◽  
Very High Cycle Fatigue ◽  
Very High

Ultrasonic fatigue tests up to 1010 cycles were performed on a turbine engine titanium alloy (Ti-8Al-1Mo-1V) at the stress ratio (R) of −1 with smooth specimens and at R = −1, 0.1 and 0.5 with notched specimens. As a result, with increase of fatigue life, the source of reduced fatigue life caused by multi-point surface crack initiation changes from crack propagation stage to crack initiation stage in the high cycle fatigue regime. Notch effect further promotes the degeneration of high cycle and very high cycle fatigue strength at R > −1. The bilinear model, extended from the Goodman method, can better estimate the mean stress sensitivity of this titanium alloy. The fatigue mean stress sensitivity and fatigue-creep mean stress sensitivity of this material increased with the increase of fatigue life. The new model, based on the Murakami model, can provide more appropriate predictions for notch fatigue strength.

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.

Effect of Heat Treatment on Very High Cycle Fatigue Properties of TC4

2021 ◽  
Vol 881 ◽  
pp. 3-11
Author(s):  
Bo Han Wang ◽  
Li Cheng ◽  
Xun Chun Bao
Keyword(s):  
Heat Treatment ◽  
High Cycle Fatigue ◽  
Treatment Method ◽  
Fatigue Performance ◽  
Fatigue Properties ◽  
Cycle Fatigue ◽  
Α Phase ◽  
Very High Cycle Fatigue ◽  
Significant Difference ◽  
Very High

The bimodal, equiaxed and Widmanstatten microstructures of TC4 titanium alloy were obtained through different heat treatment processes. The content of primary α phase in the bimodal and equiaxed microstructures was measured to be about 40% and 90%, and the average size was about 9.4μm and 7.9 μm. Three types of microstructure fatigue S-N curves are obtained, which are successively descending type, single-platform descending type and infinite life type. The order of very high cycle fatigue performance is Widmanstatten>equiaxed>bimodal, but the anti-fretting fatigue performance of Widmanstatten is the worst. The grain refinement makes the fatigue performance of the equiaxed better than that of the bimodal. The second process is determined as the best heat treatment method. There is no significant difference in the life of the crack propagation stage. The very high cycle fatigue life mainly depends on the crack initiation stage. In the bimodal and the equiaxed, the crack initiates in the primary α phase of the subsurface, and the crack in the Widmanstatten initiates in the coarse α 'grain boundary of the subsurface.

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