Effect of Hydrogen Gas on the Growth of Small Fatigue Crack in JIS-SCM435

2014 ◽  
Vol 891-892 ◽  
pp. 942-947
Author(s):  
Hisatake Itoga ◽  
Hisao Matsunaga ◽  
Saburo Matsuoka
Keyword(s):  
Fatigue Crack ◽  
Crack Growth ◽  
Ambient Air ◽  
Compact Tension ◽  
Fatigue Tests ◽  
Hydrogen Gas ◽  
Small Crack ◽  
Strain Intensity ◽  
Small Fatigue Crack ◽  
Small Cracks

The fatigue crack growth (FCG) from a small hole in a low alloy steel JIS-SCM435 round bar was investigated using tension-compression fatigue tests in 0.7 MPa hydrogen gas and ambient air. In the higher FCG rate regime (e.g. da/dN > 108 m/cycle), FCG was accelerated in hydrogen gas compared to in air. On the other hand, in the lower FCG rate regime (e.g. da/dN < 108 m/cycle), FCG in hydrogen was rather slower than that in air. There was no noticeable difference in fatigue limits between these two atmospheres. The FCG in the respective atmospheres showed a typical small crack behavior, i.e. the da/dN for small cracks were much greater than those for large cracks obtained by compact tension (CT) specimen when they were compared at the same ΔK level. In order to unify such a discrepancy of FCG behavior between small crack and large crack, the strain intensity factor range ΔKε was adopted. As a result, the da/dN data for various crack sizes was gathered in a narrow band, i.e. the small crack effect was successfully evaluated with the strain intensity. Moreover, the crack growth life was predicted based on the da/dN-ΔKε relation. The reproduced S-N curve showed a conservative agreement with the fatigue life obtained by experiments.

The Effect of Microstructure on the Hydrogen-Assisted Fatigue of Pipeline Steels

2013 ◽  
Author(s):  
Andrew J. Slifka ◽  
Elizabeth S. Drexler ◽  
Douglas G. Stalheim ◽  
Robert L. Amaro ◽  
Damian S. Lauria ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
High Pressures ◽  
Load Ratio ◽  
Fatigue Tests ◽  
Hydrogen Gas ◽  
The Other ◽  
Stress Intensity Factor Range ◽  
Pipeline Steels

Tests on the fatigue crack growth rate were conducted on four pipeline steels, two of grade API 5L-X52 and two API 5L-X70. One X52 material was manufactured in the mid-1960s and the other was manufactured in 2011. The two X70 materials had a similar vintage and chemistry, but the microstructure differs. The fatigue tests were performed in 5.5 and 34 MPa pressurized hydrogen gas, at 1 Hz and (load ratio) R = 0.5. At high pressures of hydrogen and high values of the stress intensity factor range (ΔK) there is no difference in the fatigue crack growth rates (da/dN), regardless of strength or microstructure. At low values of ΔK, however, significant differences in the da/dN are observed. The older X52 material has a ferrite-pearlite microstructure; whereas, the modern X52 has a mixture of polygonal and acicular ferrites. The X70 materials are both predominantly polygonal ferrite, but one has small amounts (∼5%) of upper bainite, and the other has small amounts of pearlite (<2%) and acicular ferrite (∼5%). We discuss the fatigue test results with respect to the different microstructures, with particular emphasis on the low ΔK regime.

scholarly journals Microstructurally small fatigue crack growth rates in aluminium alloys for developing improved predictive models

2018 ◽  
Vol 165 ◽  
pp. 13004
Author(s):  
Madeleine Burchill ◽  
Simon Barter ◽  
Lok Hin Chan ◽  
Michael Jones
Keyword(s):  
Fatigue Crack ◽  
Crack Growth ◽  
Growth Rates ◽  
Small Crack ◽  
Fatigue Crack Nucleation ◽  
Standard Material ◽  
Growth Phenomenon ◽  
Small Cracks ◽  
Small Crack Growth ◽  
Crack Growth Rates

The fatigue or durability life of a few critical structural metallic components often sets the safe and/or economic useful life of a military airframe. In the case of aluminium airframe components, growth rates, at or soon after fatigue crack nucleation are being driven by near threshold local cyclic stress intensities and thus are very low. Standard crack growth rate data is usually generated from large cracks, and therefore do not represent the growth of small cracks (typically <1mm). Discussed here is an innovative test and analysis technique to measure the growth rates of small cracks growing as the result of stress intensities just above the cyclic growth threshold. Using post-test quantitative fractographic examination of fatigue crack surfaces from a series of 7XXX test coupons, crack growth rates and observations of related growth phenomenon in the threshold region have been made. To better predict small crack growth rates under a range of aircraft loading spectra a method by which standard material data models could be adapted is proposed. Early results suggest that for small cracks this method could be useful in informing engineers on the relative severity of various spectra and leading to more accurate predictions of small crack growth rates which can dominate the fatigue life of airframe components.

Analysis of Small Fatigue Crack in Al-Mg-Si Aluminum Alloy

2014 ◽  
Vol 794-796 ◽  
pp. 313-318 ◽  
Author(s):  
Takahiro Shikama ◽  
Shinji Yoshihara ◽  
Yoshimasa Takahashi ◽  
Hiroshi Noguchi
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Crack Growth ◽  
Fatigue Limit ◽  
Electron Back Scatter Diffraction ◽  
Small Crack ◽  
Small Fatigue Crack ◽  
Knee Point ◽  
Small Crack Growth ◽  
Diffraction Patterns

In general, aluminum alloy does not exhibit distinct fatigue limit (knee point) in the S-N diagram. The growth of a small fatigue crack of precipitation-hardened Al-Mg-Si system alloy (6061-T6) was investigated to clarify the mechanism of non-appearance of distinct fatigue limit (knee point) in the S-N diagram. The small crack was analysed in detail by replica method, scanning electron microscope (SEM), and Electron Back Scatter Diffraction Patterns (EBSD). On the other hand, the existence of distinct fatigue limit (knee point) of new developed aluminum alloy by adding excess Mg to the 6061 alloy was found. In this study, the resistance of small crack growth of the developed alloy was compared with standard 6061 alloy. It was revealed that the resistance of crack growth of new developed alloy was higher than that of standard 6061 alloy in short crack region (l<1.0 mm).

An Experiment of Fatigue Crack Growth under Different R-Ratio for 2024-T4 Aluminum Alloy

2011 ◽  
Vol 66-68 ◽  
pp. 1477-1482 ◽  
Author(s):  
Guang Yang ◽  
Zeng Liang Gao ◽  
Feng Xu ◽  
Xiao Gui Wang
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Great Influence ◽  
Ambient Air ◽  
Compact Tension ◽  
Growth Region ◽  
Paris Law ◽  
Growth Experiments

The fatigue crack growth tests of compact tension (CT) specimens of 2024-T4 aluminum alloy were conducted under constant amplitude loading with differentR-ratios, 0.05, 0.1, 0.5, 0.75, respectively. The thickness of the specimen is 3.8mm. All the fatigue crack growth experiments were carried out in ambient air without a pre-crack. The early crack growth region reflects the influence of the notch. An optical reading micrometer with a magnification of 40 was used to measure the crack length. The size of the notch together with the loading conditions has a great influence on the early crack growth within the notch influenced region. Beyond the notch influenced zone, the stable fatigue crack growth is reached and can be characterized by the Paris law. The experimental results indicate that fatigue crack growth rate increases with theR-ratio for a given stress intensity factor amplitude.

Fatigue Crack Propagation Mechanisms of Long and Small Cracks in Al-Si-Mg and Al-Mg Cast Alloys

2009 ◽  
Vol 618-619 ◽  
pp. 563-574 ◽  
Author(s):  
Diana A. Lados
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Volume Fraction ◽  
Damage Threshold ◽  
Compact Tension ◽  
Threshold Behaviour ◽  
Eutectic Si ◽  
Cast Alloys ◽  
Small Cracks

Fatigue crack growth of long and small cracks was investigated for various Al-Si-Mg and Al-Mg cast alloys. Low residual stress was ensured during processing to concentrate on microstructural effects on crack growth. Compact tension and single edge tension specimens were fatigue crack growth tested at room temperature and stress ratio, R = 0.1. Microstructure related mechanisms were used to explain the near-threshold behaviour and crack growth response in Regions II and III for each material considering relevant microstructural features such as SDAS, grain size, and volume fraction and morphology of eutectic Si. Threshold behaviour of long cracks is attributed to closure-dependent mechanisms. In Regions II and III, the changes in crack growth mechanisms were explained through correlations between the extent of the plastic zone ahead of the crack tip and material-specific microstructural damage. Threshold behaviour of small cracks is explained through closure-independent mechanisms, specifically through the barrier effects of controlling microstructural characteristics specific to each material. Recommendations for integrating materials knowledge in structural design for fatigue performance are given.

Corrosion-Fatigue Crack Growth in Age-Hardened Al Alloys: Examples of Failures and Explanations for Fractographic Observations

2014 ◽  
Vol 891-892 ◽  
pp. 248-253 ◽  
Author(s):  
Rohan Byrnes ◽  
Noel Goldsmith ◽  
Mark Knop ◽  
Stan Lynch
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Corrosion Fatigue ◽  
Compact Tension ◽  
Al Alloys ◽  
Corrosion Fatigue Crack ◽  
Crack Tips ◽  
Corrosion Fatigue Crack Growth ◽  
Additional Support

The characteristics of corrosion-fatigue in age-hardened Al alloys, e.g. brittle striations on cleavage-like facets, are described, with reference to two examples of component failure. Mechanisms of corrosion fatigue (and explanations for fracture-surface features) are then reviewed. New observations of corrosion-fatigue crack growth for 7050-T7451 alloy compact-tension specimens tested in aqueous environments using a constant (intermediate) ΔK value but different cycle frequencies are then described and discussed. These observations provide additional support for a hydrogen-embrittlement process involving adsorption-induced dislocation-emission from crack tips.

scholarly journals Small Fatigue Crack Growth Mechanisms and Interfacial Stability in Cold-Spray 6061 Aluminum Alloys and Coatings

2018 ◽  
Vol 49 (12) ◽  
pp. 6509-6520 ◽  
Author(s):  
Anastasios G. Gavras ◽  
Diana A. Lados ◽  
Victor K. Champagne ◽  
Robert J. Warren ◽  
Dileep Singh
Keyword(s):  
Fatigue Crack ◽  
Aluminum Alloys ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Cold Spray ◽  
Interfacial Stability ◽  
Growth Mechanisms ◽  
Small Fatigue Crack
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