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 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 Application of a √ area -Approach for Fatigue Assessment of Cast Aluminum Alloys at Elevated Temperature

Metals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 1033 ◽  
Author(s):  
Roman Aigner ◽  
Christian Garb ◽  
Martin Leitner ◽  
Michael Stoschka ◽  
Florian Grün
Keyword(s):  
Elevated Temperature ◽  
Fatigue Strength ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Damage Mechanism ◽  
Cyclic Fatigue ◽  
Fatigue Tests ◽  
Cast Aluminum ◽  
Fatigue Assessment ◽  
Cast Aluminum Alloys

This paper contributes to the effect of elevated temperature on the fatigue strength of common aluminum cast alloys EN AC-46200 and EN AC-45500. The examination covers both static as well as cyclic fatigue investigations to study the damage mechanism of the as-cast and post-heat-treated alloys. The investigated fracture surfaces suggest a change in crack origin at elevated temperature of 150 ∘ C. At room temperature, most fatigue tests reveal shrinkage-based micro pores as their crack initiation, whereas large slipping areas occur at elevated temperature. Finally, a modified a r e a -based fatigue strength model for elevated temperatures is proposed. The original a r e a model was developed by Murakami and uses the square root of the projected area of fatigue fracture-initiating defects to correlate with the fatigue strength at room temperature. The adopted concept reveals a proper fit for the fatigue assessment of cast Al-Si materials at elevated temperatures; in detail, the slope of the original model according to Murakami should be decreased at higher temperatures as the spatial extent of casting imperfections becomes less dominant at elevated temperatures. This goes along with the increased long crack threshold at higher operating temperature conditions.

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

High-Cycle Fatigue Life of AZ31 and AZ61 Magnesium Alloys

2013 ◽  
Vol 211 ◽  
pp. 83-88
Author(s):  
Marek Cieśla
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Magnesium Alloys ◽  
High Cycle Fatigue ◽  
Fatigue Tests ◽  
Test Material ◽  
Cycle Fatigue ◽  
Structural Components ◽  
Asymmetry Coefficient ◽  
Fatigue Fractography

Usefulness of the magnesium alloys for construction of structural components is determined, apart from their low density, by a number of favourable mechanical properties and in the case of their use for components of transport means additionally by good fatigue strength. In this study, 12 mm diameter extruded rods of AZ31 and AZ61 magnesium alloys were used as test material. After extrusion the rods were annealed at a temperature of 400°C, with a 60 min soaking period and subsequent cooling in air. Cylindrical specimens with a diameter of d0 = 8 mm were made for the fatigue test under high-cycle rotary bending conditions with the cycle asymmetry coefficient R = -1. The tests were carried out for a limited fatigue strength range. Examination of microstructure of tested alloys and fatigue fractography were also performed. During the high-cycle fatigue tests it was found that the AZ61 alloy has a longer fatigue life. Based on the obtained results, fatigue life characteristics of the tested materials were drawn up.

scholarly journals Influence of discontinuities on fatigue strength using the example of additively manufactured specimens made of AlSi10Mg

2021 ◽  
Vol 349 ◽  
pp. 02010
Author(s):  
Heinz Thomas Beier ◽  
Patrick Yadegari ◽  
Michael Vormwald
Keyword(s):  
Fatigue Strength ◽  
Fracture Mechanics ◽  
High Cycle Fatigue ◽  
Local Stress ◽  
Local Strain ◽  
Fatigue Tests ◽  
Test Series ◽  
Local Problem ◽  
Cycle Fatigue ◽  
The Common

Fatigue strength is largely affected by the influence of discontinuities: geometric notches like holes and corners in components, surface notches (roughness), pores and inclusions in the material. Therefore fatigue of structures and materials is a local problem and fatigue strength calculations are best carried out using local approaches such as local stress concept, local strain concept or fracture mechanical concepts. In this investigation, the influence of discontinuities on low cycle and high cycle fatigue strength of materials was examined on the example of additively produced material specimens made of aluminium AlSi10Mg by using a fracture mechanics parameter. Results of fatigue tests on hourglass-specimens made from four different series of 3-D printed specimens are presented. The examination of the fracture surfaces revealed that damage always started from pores located near the surface of the specimens. The fractography gave information about geometry, size and position of the crack-causing pores. The influence of such pores on the fatigue strength of the printed aluminium was investigated by using a modification of Murakami’s √area parameter. The common scatter band of the four test series could thus be reduced significantly.

scholarly journals Effect of Aqueous Environment on High Cycle and Very-High-Cycle Fatigue Behavior for a Structural Steel

2011 ◽  
Vol 462-463 ◽  
pp. 355-360
Author(s):  
You Shi Hong ◽  
Gui An Qian
Keyword(s):  
Fatigue Strength ◽  
Structural Steel ◽  
High Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Fatigue Tests ◽  
Aqueous Environment ◽  
Cycle Fatigue ◽  
Very High Cycle Fatigue ◽  
Very High

In this paper, rotary bending fatigue tests for a structural steel were performed in laboratory air, fresh water and 3.5% NaCl aqueous solution, respectively, thus to investigate the influence of environmental media on the fatigue propensity of the steel, especially in high cycle and very-high-cycle fatigue regimes. The results show that the fatigue strength of the steel in water is remarkably degraded compared with the case tested in air, and that the fatigue strength in 3.5% NaCl solution is even lower than that tested in water. The fracture surfaces were examined to reveal fatigue crack initiation and propagation characteristics in air and aqueous environments.

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.

Microstructural properties and mechanical behavior of magnesium/hydroxyapatite biocomposite under static and high cycle fatigue loading

2017 ◽  
Vol 52 (13) ◽  
pp. 1711-1722 ◽  
Author(s):  
AS Sabet ◽  
AH Jabbari ◽  
M Sedighi
Keyword(s):  
High Cycle Fatigue ◽  
Particle Distribution ◽  
Testing Machine ◽  
Hot Extrusion ◽  
Fatigue Loading ◽  
Stir Casting ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Compression Tests ◽  
Tension And Compression

In this study, magnesium/hydroxyapatite biocomposites having 2.5 and 5 wt% of hydroxyapatite have been fabricated using stir casting followed by hot extrusion method. Both microstructural and mechanical behaviors of these composites have been studied, which contain particle distribution, grain size, microhardness, tension, and compression tests. Then, high cycle fatigue tests were performed using a rotating-bending testing machine (under stress ratio of R = −1). The results indicate an acceptable particle distribution and grain refinement in the composites. Also, the microhardness of the composites has been increased in comparison with the pure extruded sample. The yield stress has been enhanced in both tension and compression tests by increasing the amount of reinforcement, while the maximum strain reduced. Moreover, the fabricated biocomposites revealed better overall high cycle fatigue life in comparison to pure Mg, and infinite life (>107 cycles) could be achieved in the composites. Scanning electron microscope images of the fracture surfaces showed that the agglomeration of hydroxyapatite particles is one of the most important criteria for crack initiation in the composites.

scholarly journals Validation of Multiaxial Fatigue Strength Criteria on Specimens from Structural Steel in the High-Cycle Fatigue Region

Materials ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 116
Author(s):  
František Fojtík ◽  
Jan Papuga ◽  
Martin Fusek ◽  
Radim Halama
Keyword(s):  
Fatigue Strength ◽  
Structural Steel ◽  
High Cycle Fatigue ◽  
Fatigue Loading ◽  
Multiaxial Fatigue ◽  
Experimental Results ◽  
Prediction Methods ◽  
Cycle Fatigue ◽  
Strength Criteria

The paper describes results of fatigue strength estimates by selected multiaxial fatigue strength criteria in the region of high-cycle fatigue, and compares them with own experimental results obtained on hollow specimens made from ČSN 41 1523 structural steel. The specimens were loaded by various combinations of load channels comprising push–pull, torsion, bending and inner and outer pressures. The prediction methods were validated on fatigue strengths at seven different numbers of cycles spanning from 100,000 to 10,000,000 cycles. No substantial deviation of results based on the selected lifetime was observed. The PCRN method and the QCP method provide best results compared with other assessed methods. The results of the MMP criterion that allows users to evaluate the multiaxial fatigue loading quickly are also of interest because the method provides results only slightly worse than the two best performing solutions.

Sign in / Sign up

Export Citation Format

Share Document