scholarly journals The linear-elastic Theory of Critical Distances to estimate high-cycle fatigue strength of notched metallic materials at elevated temperatures

2014 ◽  
Vol 38 (6) ◽  
pp. 629-640 ◽  
Author(s):  
R. Louks ◽  
L. Susmel
Keyword(s):  
Fatigue Strength ◽  
High Cycle Fatigue ◽  
Elevated Temperatures ◽  
Elastic Theory ◽  
Metallic Materials ◽  
Cycle Fatigue ◽  
Linear Elastic ◽  
Linear Elastic Theory

OS1514 High-Cycle Fatigue Strength of Modified 9Cr-1Mo Steel at Elevated Temperatures

2013 ◽  
Vol 2013 (0) ◽  
pp. _OS1514-1_-_OS1514-3_
Author(s):  
Motoyuki OCHI ◽  
Ken SUZUKI ◽  
Isamu NONAKA ◽  
Hideo MIURA
Keyword(s):  
Fatigue Strength ◽  
High Cycle Fatigue ◽  
Elevated Temperatures ◽  
Cycle Fatigue

Elucidation of the High Cycle Fatigue Damage Mechanism of Modified 9Cr-1Mo Steel at Elevated Temperature

2015 ◽  
Author(s):  
Takuya Murakoshi ◽  
Motoyuki Ochi ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Fatigue Strength ◽  
High Cycle Fatigue ◽  
Elevated Temperatures ◽  
Surface Hardness ◽  
Diffraction Method ◽  
Fatigue Loading ◽  
Damage Mechanism ◽  
Fatigue Tests ◽  
Electron Back Scatter Diffraction ◽  
Cycle Fatigue

Modified 9Cr-1Mo steel is one of the heat-resistant steels developed for steam generator in a FBR (Fast Breeder Reactor). When it is used in a FBR, the lifetime of the steel under HCF (High Cycle Fatigue) and V-HCF (Very-High Cycle Fatigue) caused by flow-induced vibration has to be considered for assuring its long-term reliability up to 1011 cycles. Since previous studies showed that the fatigue limit did not appear up to 108 cycles, it is necessary to investigate the fatigue strength of this alloy in cycles higher than 108 cycles. In this study, in order to clarify high cycle fatigue strength and fracture mechanism of the modified 9Cr-1Mo steel, the change of the lath martensitic strengthening structure was observed in detail on the surface of specimens fractured by rotary bending fatigue tests by using EBSD (Electron Back-Scatter Diffraction) method. The Kernel Average Misorientation (KAM) value obtained from the EBSD analysis was used for the quantitative evaluation of the change of the lath martensitic texture. It was found that the average KAM values clearly decreased on the surface areas of the fractured specimens after the application of 107-108 cycles of fatigue loading at temperatures higher than 550°C. This result indicates that degradation of the lath martensitic texture occurred around the surface of specimens tested at the temperature higher than 550°C. In order to quantitatively evaluate the decrease of its strength, a hardness test was performed at room temperature by using a nanoindentation method. It was confirmed that the surface hardness of specimens decreased drastically in the specimens fractured at temperatures higher than 550°C. From these results, it was concluded that the effective 0.2%-proof stress decreased during the fatigue tests by the degradation of the lath martensitic texture caused by the fatigue loading at elevated temperatures. Further analyses are indispensable for explicating the damage mechanism more in detail.

High Cycle Fatigue Properties of Modified 9Cr-1Mo Steel at Elevated Temperatures

2012 ◽  
Author(s):  
Yoshiaki Matsumori ◽  
Jumpei Nemoto ◽  
Yuji Ichikawa ◽  
Isamu Nonaka ◽  
Hideo Miura
Keyword(s):  
Fatigue Strength ◽  
Fatigue Limit ◽  
Room Temperature ◽  
Structural Reliability ◽  
High Cycle Fatigue ◽  
Elevated Temperatures ◽  
Fatigue Behavior ◽  
Cyclic Softening ◽  
Fatigue Properties ◽  
Cycle Fatigue

Since high-cycle fatigue loads is applied to the pipes in various energy and chemical plants due to the vibration and frequent temperature change of fluid in the pipes, the high-cycle fatigue behavior of the alloys used for pipes should be understood quantitatively in the structural reliability design of the pipes. The purpose of this study, therefore, is to clarify the high-cycle fatigue strength and fracture mechanism of the modified 9Cr-1Mo steel at temperatures higher than 400°C. This material is one of the effective candidates for the pipes in fast breeder demonstration reactor systems. A rotating bending fatigue test was applied to samples at 50 Hz in air. The stress waveform was sinusoidal and the stress ratio was fixed at −1. The fatigue limit was observed at room temperature and it was about 420 MPa. This value was lower than the 0.2% proof stress of this alloy by about 60 MPa. This decrease can be attributed to the cyclic softening of this material. The limited cycles at knee point was about 8×105 cycles. All fracture was initiated from a single surface crack and no inclusion-induced fracture was observed in the fracture surface by SEM. Thus, the high-cycle fatigue design based on the fatigue limit may be applicable to the modified 9Cr-1Mo steel at room temperature. The fatigue limit of about 350 MPa was also observed at 400°C, and it appeared at about 107 cycles, while it appeared at around 106 cycles at room temperature. Thus, it was confirmed that the fatigue strength of this alloy decrease with temperature. However, the fatigue limit didn’t appear at 550°C up to 108 cycles. The fatigue limit may disappear in this alloy at 550°C. It is very important, therefore, to evaluate the ultra-high cycle fatigue strength of this alloy at temperatures higher than 400°C.

Notch Fatigue and Fracture Mechanics of Austempered Ductile Irons

2010 ◽  
Vol 457 ◽  
pp. 181-186 ◽  
Author(s):  
Bruno Atzori ◽  
Franco Bonollo ◽  
Giovanni Meneghetti
Keyword(s):  
Fatigue Strength ◽  
Fracture Mechanics ◽  
High Cycle Fatigue ◽  
Peak Stress ◽  
Fatigue Behaviour ◽  
Cycle Fatigue ◽  
Elastic Peak ◽  
Linear Elastic ◽  
Design Engineers ◽  
Notch Tip

In this paper the fatigue characterization of an austempered ductile iron (ADI) is presented. The aim of the work is to provide design engineers involved in fatigue assessments with an engineering tool suitable to deal with notches of different severity. Classically, U-notches are divided into blunt notches and sharp notches. The former are characterized by large notch tip radii such that the high cycle fatigue strength is controlled by the elastic peak stress, i.e. by the elastic stress concentration factor. The latter are characterized by reduced notch tip radii such that the effective stress which controls the high cycle fatigue strength is significantly lower than the elastic peak stress and their behaviour become similar to that of a crack having the same length. Blunt notches are assessed according to the classical Notch Mechanics principles, while sharp notches are treated with the Linear Elastic Fracture Mechanics approach. After presenting the classical Frost diagram which highlights the different fatigue behaviour of sharp and blunt notches, fatigue test results generated from notches of different severity are presented as well as a synthesis in a diagram able to account for short cracks/notches, long cracks, sharp notches and blunt notches.

High Cycle Fatigue Strength of Modified 9Cr-1Mo Steel at Elevated Temperatures

2014 ◽  
Author(s):  
Motoyuki Ochi ◽  
Ken Suzuki ◽  
Isamu Nonaka ◽  
Hideo Miura
Keyword(s):  
Fatigue Strength ◽  
Fatigue Limit ◽  
Room Temperature ◽  
High Cycle Fatigue ◽  
Elevated Temperatures ◽  
Fatigue Loading ◽  
Bending Test ◽  
Cycle Fatigue ◽  
Intergranular Cracking

In order to clarify the characteristics of high-cycle fatigue of the modified 9Cr-1Mo steel, a high temperature rotary bending test was carried out. As a result, the fatigue strength of this alloy decreased monotonically at elevated temperatures. It decreased from 440 MPa at room temperature to about 350 MPa at 400°C. This decrease of the fatigue strength was attributed to the temperature dependence of the yielding strength of this alloy. The fatigue limit appeared near 107 cycles at 400°C, whereas it appeared around 106 cycles at room temperature. The most important result is that the fatigue limit disappeared up to 108 cycles at temperatures higher than 500°C. Thus, the number of cycles at which the fatigue limit appeared shifted to higher cycles with increasing the testing temperature. Clear striation was observed in the stable crack growth region on the fracture surface of all the specimen tested at room temperature, 400°C, 500°C, 550°C, and 600°C. Intergranular cracking, which have been observed in creep-fatigue tests, was not observed. Since the estimated operating temperature of FBR is 550°C, it is very important to consider this fatigue strength in the structural and reliability design of the modified 9Cr-1Mo steel. In this study, the change of crystallinity of this alloy under fatigue loading was also analyzed by applying an EBSD method. The image quality (IQ) value obtained from the analysis was used for the quantitative evaluation of the crystallinity in the area where an electron beam of 20 nm in diameter was irradiated. The quality of the atomic alignment was found to degrade under the cyclic loading, and a crack started to occur on the surface of the alloy when the quality of the atomic alignment decreased to a certain critical value.

scholarly journals A multiaxial prediction equation of low/medium/high cycle fatigue life of metallic materials for plain and notch components

2021 ◽  
Author(s):  
xiangqiao yan
Keyword(s):  
Experimental Data ◽  
Fatigue Life ◽  
High Cycle Fatigue ◽  
Prediction Equation ◽  
Elastic Analysis ◽  
Metallic Materials ◽  
Cycle Fatigue ◽  
Linear Elastic ◽  
Mechanical Quantity ◽  
Stress Invariant

In this paper, it is important to illustrate that, for the LCF of metallic materials, a “stress quantity” calculated based on the linear-elastic analysis of the studied component is taken to be a mechanical quantity, S, to establish a relation of the mechanical quantity, S, to the fatigue life, N, is practicable. Based on the practicability, a prediction equation, for a low/medium/high cycle fatigue life assessment of metallic materials, is proposed. The prediction equation is a stress invariant based one, in which the computation of stress invariant is on the basis of the linear-elastic analysis of the studied component. Using experimental data of plain specimens reported in literature, it is proved that the prediction equation is both accurate and high efficient. In addition, the prediction equation in conjunction with the Theory of Critical Distances and linear-elastic notch mechanics are combined to establish the fatigue life estimation equation of the notched components. Finally, using experimental data of the fatigue life of 16MnR steel, validation verification of the notch fatigue life prediction equation is given.

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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