scholarly journals A CRITICAL DEPTH CRITERION FOR THE EVALUATION OF LONG-LIFE FATIGUE STRENGTH UNDER MULTIAXIAL LOADING AND A STRESS GRADIENT

Fracture 84 ◽  
1984 ◽  
pp. 1887-1894 ◽  
Author(s):  
J.F. Flavenot ◽  
N. Skalli
Keyword(s):  
Fatigue Strength ◽  
Stress Gradient ◽  
Multiaxial Loading ◽  
Critical Depth ◽  
Long Life

Fatigue Strength Assessment of a Structure Considering Corrosion Wastage and Corrosion Fatigue

2018 ◽  
Author(s):  
Norio Yamamoto ◽  
Tomohiro Sugimoto ◽  
Kinya Ishibashi
Keyword(s):  
Fatigue Crack ◽  
Fatigue Strength ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Corrosion Fatigue ◽  
Life Assessment ◽  
Actual State ◽  
Corrosive Environment ◽  
Corrosion Fatigue Crack ◽  
Long Life

It is known that the fatigue strength decreases in corrosive environment and many experiments were carried out to comprehend the decrease in fatigue strength in corrosive environment. In order to comprehend the actual state, a cycle speed of fatigue test loads should correspond to a wave frequency. Therefore, an experiment in the long life region is practically difficult, then the corrosion fatigue data available for the life assessment of the structure is quite limited. In this study, the fatigue strength of the welded joints in long life service was evaluated according to the calculations of corrosion fatigue crack propagation subjected to the random loadings which followed an exponential distribution. In the crack propagation calculations, the progress of corrosion wastage from the plate surface and the resultant stress increase were considered simultaneously. In the high stress and the short life region, the decrease in fatigue strength due to the accelerated crack propagation in corrosive environment was dominant because the progress of corrosion wastage was little. On the other hand, in the low stress and the long life region, the decrease in fatigue strength became dull as longer the fatigue life because the corrosion fatigue crack propagation was suppressed by the corrosion wastage, but after that the fatigue strength showed the precipitous decrease due to the increase in stress resulted by the progress of corrosion wastage.

scholarly journals Long-Life Fatigue of Carburized 12Cr2Ni Alloy Steel: Evaluation of Failure Characteristic and Prediction of Fatigue Strength

Metals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 1006 ◽  
Author(s):  
Hailong Deng ◽  
Qichen Liu ◽  
Hang Liu ◽  
Huan Yu
Keyword(s):  
Fatigue Strength ◽  
Fatigue Limit ◽  
Alloy Steel ◽  
Extreme Values ◽  
Crack Size ◽  
Point Of View ◽  
Statistical Point ◽  
Surface Failure ◽  
Material Hardness ◽  
Long Life

In this study, the fatigue failure behaviors of carburized 12Cr2Ni alloy steel were examined in the long-life regime between 104 and 108 cycles with about 100 Hz under R = 0. Results showed that this alloy steel exhibited the double S-N characteristics with surface failure and interior failure. From a statistical point of view, the correlation coefficient further proved that the fine granular area (FGA) governed the fatigue performance of carburized 12Cr2Ni alloy steel. Based on the generalized extreme values (GEV) distribution and test data, the predicted maximum defect size was about 23.4 μm. Considering the effect of tensile limit, material hardness, and crack size characteristics, the fatigue strength prediction model under stress ratio of 0 could be established. The predicted fatigue limit for carburized 12Cr2Ni alloy steel at 108 cycles under R = 0 was 507.86 MPa, and the prediction error of fatigue limit was within 0.04. Therefore, the results were extremely accurate.

The Influence of Notch Geometric Size in the Fatigue Strength of Steel

2014 ◽  
Vol 602-605 ◽  
pp. 167-171
Author(s):  
Yong Zhuang Yuan
Keyword(s):  
Fatigue Strength ◽  
Fatigue Behavior ◽  
Stress Gradient ◽  
Fatigue Crack Initiation ◽  
Estimation Method ◽  
Size Factor ◽  
Linear Elastic ◽  
Factor Effect ◽  
Geometric Size ◽  
Elastic Fracture

The fatigue behavior of notch specimens has been investigated in this manuscript. It is shown that notch geometric size has apparent effect for fatigue strength of specimens. The blunt notch is used in test. It is concluded that geometric size effect depends on the stress gradient and can be estimated with the help of the linear elastic fracture mechanics. The influence of notch size for fatigue strength can be explained with geometric factor. The plastic strain play an important role in fatigue crack initiation with notch gets sharper reach certain magnitude limit, and fatigue strength is lower than the predicted by geometric size factor effect. The method does not apply fatigue strength of the sharper notch. Another estimation method shall be used to that kind of notches.

Effect of Specimen Size and Preparation on the Fatigue Strength of a Plain Carbon Steel Tested in Rotating Bending and in Torsion

1970 ◽  
Vol 185 (1) ◽  
pp. 655-664 ◽  
Author(s):  
D. A. Kelly ◽  
J. L. M. Morrison
Keyword(s):  
Fatigue Strength ◽  
Size Effect ◽  
Stress Gradient ◽  
Plain Carbon Steel ◽  
Specimen Preparation ◽  
Minimum Diameter ◽  
Heat Treated ◽  
High Fatigue ◽  
Extensive Test ◽  
Rotating Bending

A survey of the literature indicates that, in the presence of a stress gradient, the fatigue strength of large components is generally less than the fatigue limit exhibited by small specimens of similar material. In some cases the ‘size effect’ reported is of alarming proportions. However, a closer examination of the literature and the results of some exploratory tests in rotating bending suggest that the effects observed may not be attributable simply to size but may also be dependent on the final stages of specimen preparation. An extensive test programme carried out on notch-free 0·32 C steel specimens, ranging in minimum diameter from 0·05 to 05 in in torsion and from 0·05 to 1·6 in in bending, provides results showing four main features. As other workers have found, very small specimens have generally high fatigue limits and as-polished specimens have higher fatigue limits than as-heat-treated specimens. For specimens that were normalized, carefully machined and polished, then stress-relieved and finally lightly repolished, the fatigue strength shows a significant increase as the diameter decreases, the maximum increases being about 15 per cent in torsion and 20 per cent in bending. For specimens finally stress-relieved the size effect, over the ranges from 0·25 in diameter upwards, is negligible.

scholarly journals Ability of multiaxial fatigue criteria accounting for stress gradient effect for surface defective material

2018 ◽  
Vol 165 ◽  
pp. 22032
Author(s):  
Wichian Niamchaona ◽  
Fabienne Pennec ◽  
Kévin Tihay ◽  
Michel Duchet ◽  
Bastien Weber ◽  
...  
Keyword(s):  
Fatigue Strength ◽  
Surface Defects ◽  
Stress Gradient ◽  
High Stress ◽  
High Strength Steels ◽  
Fatigue Behaviour ◽  
Multiaxial Fatigue ◽  
Integral Approach ◽  
Manufacturing Defects ◽  
Material Fatigue

New high strength steels are widely used nowadays in many industrial areas as in automotive industry. These steels are more resistant and provide higher fatigue limits than latter ones but they are also more sensible to small defects. Natural defects that outcome from metallurgy (as shrinkage, inclusion, void) are not considered in this study. We focus on small manufacturing defects such as cutting edge defects generated by punching or other surface defects due to stamping. These defects are harmful on the material fatigue behaviour due to high stress concentration at defects root. They also generate stress gradient that is beneficial from the fatigue strength point of view. This study focusses on the stress gradient (it does not account for the size effect) from cylindrical defect on specimen edge. Practically a normal stress gradient is added in multiaxial fatigue criteria formulation. Both critical plane approach and integral approach are involved in the present study. This gradient is calculated from stress states at defects root by using FEM. Criteria fatigue function at N cycles is used to assess the material fatigue strength. Obviously multiaxial fatigue criteria accounting for stress gradient give more precise fatigue functions than criteria that do not consider the gradient influence.

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