Modeling High Crack Growth Rates under Variable Amplitude Loading

2009 ◽  
pp. 214-214-20 ◽  
Author(s):  
DJ Dougherty ◽  
AU de Koning ◽  
BM Hillberry
Keyword(s):  
Crack Growth ◽  
Growth Rates ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
High Crack ◽  
Crack Growth Rates

Prediction of Fatigue Crack Growth of Aged Hardening Al-Alloys under Variable Amplitude Loading

2014 ◽  
Vol 891-892 ◽  
pp. 1729-1735
Author(s):  
Mustapha Benachour ◽  
Boumedienne Zeggai ◽  
Nadjia Benachour ◽  
Mohamed Benguediab ◽  
Abdelkader Belmokhtar
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Al Alloys ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
R Ratio ◽  
Single Overload ◽  
Crack Growth Rates

In this investigation, variable amplitude loading effect was studied on aged hardening Al-alloys in series 2000 and 7000. Generalised Willenborg model was used in order to show loading interaction effects (overload effects). Variable amplitude loading under different form of spectrum has affected highly the fatigue life and fatigue crack growth rates. Fatigue lives were increased and fatigue crack growth rates (FCGRs) were decreased in increasing of overload ratio in single overload case. In application of overload band, the fatigue lives and FCGRs were affected by band overload and R-ratio of them when level in FCGRs was increased.

Small Scale Sour Fatigue Testing With Dense Phase Gases

2012 ◽  
Author(s):  
Weiwei Yu ◽  
Pedro M. Vargas ◽  
Ben Crowder ◽  
Sam Mishael ◽  
Ramgopal Thodla
Keyword(s):  
Growth Rate ◽  
High Pressure ◽  
Water Content ◽  
Crack Growth ◽  
Growth Rates ◽  
Fatigue Performance ◽  
Small Scale ◽  
Dense Phase ◽  
High Crack ◽  
Crack Growth Rates

One way generally accepted by industry to evaluate the effect of sour environment on fatigue performance of girth welds is by small scale testing in sour brines. These tests are commonly done at room temperature and pressure and therefore can only contain a maximum of 14.7psia of H2S in a gaseous phase. In comparison, very little has been published about fatigue performance in sour environments where negligible amounts or no water is present. Such condition can be found for pipelines serving in a “dry” sour environment (H2S and other gases in dense phase) with high H2S concentration. This paper documents both small scale fatigue crack growth rate (FCGR) tests and S-N fatigue tests in a dense phase sour environment with ultra-low water content and high H2S concentration under high pressure. Fatigue life reduction factors were calculated from FCGR approach (with the name crack growth acceleration factor, CGAF) and S-N approach (with the name knockdown factor), respectively. Industry understanding today is that water is necessary for accelerating fatigue crack growth. Quite opposite to the expected effect of water content on crack growth, even ultra-low water content (<450ppm) resulted in high crack growth rates. Crack growth rates were comparable among tests with various water contents, all ultra low. Through limited testing, no temperature dependency on crack growth rate was identified. It is postulated that hydrogen dissociation due to high pressure and high concentration may be the cause for high crack growth rates on the absence of water. Small scale S-N tests on smooth specimens reveal that fatigue performance in ultra-low-water sour environments is the same as in air. We find that the dry gas environment dose not attack the metal surface preserving the fatigue performance.

scholarly journals Fatigue Behaviour in Fine Grained Aluminium Alloys

2006 ◽  
Vol 519-521 ◽  
pp. 1077-1082 ◽  
Author(s):  
L.J. Venning ◽  
I. Sinclair ◽  
P.A.S. Reed
Keyword(s):  
Crack Growth ◽  
Growth Rates ◽  
Volume Fraction ◽  
High Volume ◽  
Fatigue Behaviour ◽  
Production Method ◽  
Fracture Surface Roughness ◽  
Fine Grained ◽  
High Crack ◽  
Crack Growth Rates

The effects of alloy production method on microstructure and hence fatigue crack growth rate and fracture mechanism have been examined for a variety of fine-grained/high dispersoid Al-Li-Mg-Zr and Al-Li-Cu-Mg-Zr alloys. Microstructures have been assessed by scanning and transmission electron microcopy, together with electron back scattered diffraction pattern assessment. In these fine-grained/high dispersoid materials, high crack growth rates are seen in comparison to the traditional DC cast alloys, excepting a material with high volume fraction of shearable precipitate. The effects of fracture surface roughness and closure levels in determining crack growth rates has been assessed.

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