Analysis of Biaxial Fatigue Crack Growth in Microstructure Modeled by Voronoi-Polygon

2007 ◽  
Vol 345-346 ◽  
pp. 211-216 ◽  
Author(s):  
Toshihiko Hoshide ◽  
Yasunori Sata
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Low Cycle Fatigue ◽  
Pure Copper ◽  
Biaxial Stress ◽  
Cracking Behavior ◽  
Adequate Model ◽  
Voronoi Polygon ◽  
Biaxial Fatigue ◽  
Failure Life

Cracking behavior in low cycle fatigue regime depends on the level and the multiaxiality of the applied stress and also on the microstructure. Such a complex cracking behavior affects failure life significantly. More realistic assessments of failure life and integrity require a new appropriate procedure to analyze the crack growth process in multiaxial fatigue. A model of the fatigue process has been proposed to describe the cracking behavior in biaxial stress state. There is, however, no adequate model to present features of material microstructure. In this work, simulations of crack initiation and propagation based on a previous model were carried out in microstructure modeled by using Voronoi-polygon. In a crack initiation analysis, slip-band crack was modeled for the slip system given randomly in each grain composing the modeled microstructure. In modeling crack growth, a competition model between the coalescence growth and the propagation as a single crack was applied. Simulated cracking morphology and failure life were compared with experimental results observed in biaxial fatigue using circumferentially notched specimens of a pure copper, and the applicability of the proposed model was discussed.

Fatigue Crack Initiation and Growth Observation for 316 Stainless Steel Subjected to Equi-Biaxial Cyclic Loading

2015 ◽  
Author(s):  
Satoshi Iida ◽  
Shigeki Abe ◽  
Takao Nakamura ◽  
Masayuki Kamaya
Keyword(s):  
Fatigue Crack ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Equivalent Stress ◽  
Fatigue Crack Initiation ◽  
Biaxial Stress ◽  
Fluid Temperature ◽  
Plant Design ◽  
Cracking Behavior ◽  
Thermal Transients

Fatigue accumulation is one of the ageing phenomena considered in the plant design and maintenance. The degree of fatigue damage is evaluated by cumulative usage factor using design fatigue curve, which is determined from results of uniaxial fatigue tests. The stress caused by thermal transients is generally equibiaxial, not uniaxial. Fluid temperature fluctuation due to changes in plant conditions, such as plant start-up and shutdown, is the primary cause of fatigue damage. For accurate fatigue damage evaluation, it is important to be conducted under equi-biaxial condition. In this study, pressurized disc fatigue test was conducted in order to simulate the cyclic equi-biaxial stress. In order to clarify how the crack initiates and grows under the equi-biaxial stress condition. Cracking behavior was examined by replica observation method. The crack growth rates were identified by the change in the crack length. It was shown that the fatigue crack growth rate under equi-biaxial stress was faster than that under uniaxial stress for the same equivalent stress intensify factor. It was concluded that the reduction in the fatigue life under equi-biaxial stress was brought about by the accelerated crack growth.

Low Cycle Fatigue Crack Initiation of Rotating Structures Under Biaxial Stress States

2009 ◽  
Author(s):  
Chao Zhang
Keyword(s):  
Stress State ◽  
Crack Initiation ◽  
Low Cycle Fatigue ◽  
Cyclic Stress ◽  
Biaxial Stress ◽  
Test Results ◽  
Primary Stress ◽  
Biaxial Stress State ◽  
Fatigue Characteristics ◽  
Stress States

Rotating structures can experience biaxial stress states with a wide range of biaxiality ratios on structure surfaces. Low cycle fatigue (LCF) crack initiation in such conditions demonstrates different fatigue characteristics in terms of crack orientation, fatigue life, etc. The biaxial stress states can be categorized into two types: in-phase and out-of-phase under which fatigue characteristics can be significantly different according to rig test results. This paper presents an investigation of LCF crack initiation under in-phase and out-of-phase biaxial stress states based on rig test results of a nickel alloy. The crack orientations are reviewed and discussed at different stress states. Relations of biaxial LCF life debit factor vs biaxiality ratio are derived (the debit factor is defined as a ratio of the LCF life at a biaxial stress state to the LCF life at corresponding uniaxial stress state which has same cyclic and mean stresses as the primary cyclic and mean stressees of the biaxial stress state). The rig test results showed that the crack orientation is usually normal to the primary stress vector under in-phase biaxial stress states but is inclined to the primary stress vector under out-of-phase stress states. As per the derived biaxial LCF life debit factors, the LCF life was found to be slightly reduced with increasing biaxiality ratios under in-phase biaxial stress states but significantly reduced under out-of-phase biaxial stress states compared with corresponding uniaxial primary stress states. The equivalent cyclic stress fatigue criterion is also employed to theoretically model the biaxial LCF life debit factor under in-phase biaxial stress states. The hydrostatic cyclic stress is included in the equivalent cyclic stress in order to take into account the hydrostatic cyclic pressure effects. The equivalent cyclic stress in the criterion can physically reflect the materials’ ductility reduction under in-phase multiaxial stress states.

Initiation and Growth of Small Fatigue Cracks of Steels Used for Nuclear Power Plants Under Low Cycle Regime

2014 ◽  
Author(s):  
Shota Hasunuma ◽  
Takeshi Ogawa
Keyword(s):  
Fatigue Crack ◽  
Fracture Mechanics ◽  
Crack Initiation ◽  
Crack Growth ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Cycle Fatigue

Low cycle fatigue tests were conducted for carbon steel, STS410, low alloy steel, SFVQ1A, and austenitic stainless steel, SUS316NG, which were used for nuclear power plants, in order to investigate the mechanism of fatigue damage when the plants were subjected to huge seismic loads. In these tests, the surface behavior of fatigue crack initiation and growth was observed in detail using cellulose acetate replicas, while the interior behavior was detected in terms of fracture surface morphology developed by multiple two-step strain amplitude variations with periodical surface removals. Fatigue crack growth rates were evaluated by elasto-plastic fracture mechanics approach. For SFVQ1A and SUS316NG, the fracture mechanics approach is available in order to predict the crack growth life from the metallurgical crack initiation size to the final crack length of the specimens. For STS410, numerous small cracks initiated, grew and coalesced each other on the specimen surface under low cycle fatigue regime.

Biaxial Low Cycle Fatigue of Unaged and Aged 1Cr-1Mo-1/4V Steels at Elevated Temperature

1991 ◽  
Vol 113 (2) ◽  
pp. 244-253 ◽  
Author(s):  
M. Sakane ◽  
M. Ohnami ◽  
M. Sawada
Keyword(s):  
Elevated Temperature ◽  
Low Cycle Fatigue ◽  
Biaxial Stress ◽  
Cycle Fatigue ◽  
Biaxial Strain ◽  
Data Correlation ◽  
Biaxial Fatigue ◽  
Fatigue Data ◽  
Effective Stress Parameter ◽  
Stress Parameters

This paper describes the biaxial low cycle fatigue of unaged and aged 1Cr-1Mo-1/4V rotor steels at 823 K in air. Combined push-pull and reversed torsion tests were carried out on these steels and the biaxial fatigue data were obtained. Aging significantly reduced the hardness of the steel but had no effect on the crack direction in biaxial low cycle fatigue. Aging also had no effect on the data correlation using the biaxial strain parameters, but had a significant effect on the data correlation using the biaxial stress parameters. The change in the effective stress parameter in correlating the biaxial fatigue data due to aging is discussed in connection with the material softening.

Crack Initiation and Growth Analysis by Direct Optical Observation during SSRT in High Temperature Water

CORROSION ◽  
1984 ◽  
Vol 40 (3) ◽  
pp. 120-126 ◽  
Author(s):  
Takashi Kawakubo ◽  
Mamoru Hishida
Keyword(s):  
High Temperature ◽  
Crack Initiation ◽  
Crack Growth ◽  
Optical Observation ◽  
Observation System ◽  
Slow Strain Rate Test ◽  
Cracking Behavior ◽  
High Temperature Water ◽  
Rate Test ◽  
Temperature Water

Abstract The stress corrosion cracking behavior during the slow strain rate test (SSRT) has been investigated in high temperature water. SSRTs were performed on center-notched thin plate specimens of sensitized Type 304 stainless steel. A direct optical observation system consisting of single crystal sapphire windows was employed to separate the SCC into an initiation and a growth stage, and to measure the crack growth rate. Effects of the extension rate, test temperature, and dissolved oxygen concentration on the crack initiation and growth were examined. The crack growth data were analyzed with different variables, including the elastic plastic fracture mechanics parameters. The best interpretation of the crack growth rates is obtained by plotting them vs the time differential of J-integral, which is an estimate of the crack tip deformation rate during SSRT.

Biaxial Low Cycle Fatigue for Notched, Cracked, and Smooth Specimens at High Temperatures

1988 ◽  
Vol 110 (1) ◽  
pp. 48-54 ◽  
Author(s):  
Masao Sakane ◽  
Masateru Ohnami ◽  
Naomi Hamada
Keyword(s):  
Low Cycle Fatigue ◽  
Equivalent Stress ◽  
Torsion Test ◽  
Maximum Principal Stress ◽  
304 Stainless Steel ◽  
Cycle Fatigue ◽  
Failure Data ◽  
Biaxial Fatigue ◽  
Failure Life ◽  
Type 304

Push-pull and reversed torsion tests were carried out for notched, precracked, and smooth hollow cylindrical specimens of type 304 stainless steel at 923K in air. This paper describes the crack direction in the three types of specimens and the parameter that correlates the biaxial low cycle fatigue failure data. All types of specimens, except the smooth specimen in the reversed torsion test, failed by mode I cracking. Failure life of the specimens was discussed in connection with the crack mode. The equivalent stress based on COD could correlate the biaxial fatigue data whereas the Mises’ equivalent stress and the maximum principal stress could not.

Fatigue Life and Fracture Behavior of Micro Size Sn-Ag-Cu Solder Joint

2011 ◽  
Author(s):  
Tashiro Naoki ◽  
Yoshiharu Kariya ◽  
Yoshihiko Kanda
Keyword(s):  
Crack Initiation ◽  
Fracture Behavior ◽  
Low Cycle Fatigue ◽  
Cyclic Strain ◽  
High Energy ◽  
Transgranular Fracture ◽  
Solder Balls ◽  
Complete Failure ◽  
Crack Initiation Life ◽  
Failure Life

The influence of the joint size on low cycle fatigue characteristic of Sn-Ag-Cu has been investigated by a micro size joint specimen fabricated using solder balls. Although the effect of joint size on crack initiation life is not obvious at 298K, the reduction of the joint size changes the cyclic strain hardening nature and the fracture behavior that induces the life reduction at 398K. With a decrease in size, the failure mechanism transforms from a transgranular fracture to an intergranular fracture at the high energy grain boundary that is formed by high angle boundary formation following dynamic recovery in whole of joint. Therefore, the failure life is greatly reduced as a complete failure occurs simultaneously with the crack initiation at the grain boundaries. This is more remarkable at higher temperatures.

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