Fatigue Microcrack Initiation and Propagation of Aluminum Alloy under Different Stress Level and Stress Ratio

2011 ◽  
Vol 239-242 ◽  
pp. 1495-1500
Author(s):  
Gui Xue Bian ◽  
Yue Liang Chen ◽  
Jian Jun Hu ◽  
Yong Zhang
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Stress Level ◽  
Stress Ratio ◽  
High Stress ◽  
Optical Microscope ◽  
Initiation And Propagation ◽  
Microcrack Initiation ◽  
Stress Ratios ◽  
High Stress Level

The microstructure of fatigue fracture of aluminum alloys under various stresses and stress ratios were studied by optical microscope and scanning electron microscope, and the influences of microstructure features on microcrack initiation and propagation were investigated. The results show that the fatigue microcrack originated from surface or subsurface of specimens. And with the increase of stress ratio, fatigue crack originated from deeper subsurface at the same stress level. With the increase of stress level, fatigue crack originated from shallower subsurface or surface at same stress ratio. There is an increase in crack propagation region as the stress level decreases at the same stress ratio. Increasing of stress ratio, increases crack propagation region under same stress level. Microcrack generally originated from secondary (S phase particles) and larger particles at low stress level and high stress ratio. Microcrack generally originated from larger constituent particles at high stress level and low stress ratio. Microcracks propagation is evidently impeded by grain boundaries at low stress level and high stress ratio.

Influence of Stress Ratio on Fatigue Crack Propagation in TiAl Alloy

2013 ◽  
Vol 457-458 ◽  
pp. 7-10 ◽  
Author(s):  
Rui Cheng Feng ◽  
Zhi Yuan Rui ◽  
Yan Rui Zuo ◽  
Guo Tao Zhang ◽  
Chang Feng Yan
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Stress Ratio ◽  
Tial Alloy ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Fatigue Crack Propagation Rate ◽  
Stress Ratios ◽  
Region Ii

Based on the experiments did by B.K.Parida and T.Nicholas [1], the fatigue crack propagation rate of TiAl alloy under different stress ratios had been tested in order to find out the role of stress ratio and to derive an improved fatigue crack propagation formula for region II(the expansion region) according to Paris formula and to calculate the specific values of the constants in the formula. The experimental results reveal that stress ratio has a significant influence on fatigue crack growth rate.

Influence of Microstructure and Stress Ratio on Fatigue Crack Propagation in TiAl Alloy

2014 ◽  
Vol 881-883 ◽  
pp. 1330-1333 ◽  
Author(s):  
Yan Rui Zuo ◽  
Zhi Yuan Rui ◽  
Rui Cheng Feng ◽  
De Chun Luo ◽  
Chang Feng Yan
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Stress Ratio ◽  
Tial Alloy ◽  
Lamellar Microstructure ◽  
Propagation Resistance ◽  
Crack Propagation Resistance ◽  
Stress Ratios ◽  
Fully Lamellar

Based on the fatigue crack propagation experiments did by A.-L. Gloanec et al., the fatigue crack propagation rates of TiAl alloy of two processing routes, namely casting and PM, and stress ratios had been tested, in order to find out the effects of microstructure and stress ratio. An improved fatigue crack propagation formula for region Ⅱ (the expansion region) was derived according to Paris formula. The specific values of the constants in the formula were calculated. Fatigue crack propagation resistance of nearly fully lamellar microstructure is superior to that of equiaxed γ grain. The experimental results present that both microstructure and stress ratio has a significant influence on fatigue crack growth rate.

Analysis on Fatigue Crack Propagation and Fractography of A7075 Aluminum Alloy

2012 ◽  
Vol 217-219 ◽  
pp. 390-394 ◽  
Author(s):  
Xu Chao ◽  
Shang Lei Yang
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Stress Amplitude ◽  
High Stress ◽  
Great Influence ◽  
Optical Microscope ◽  
Secondary Cracks ◽  
Fatigue Fractography

The fatigue fractography and surface of A7075 aluminum alloy was investigated by means of optical microscope, scanning electron microscope and technology of metallurgic replica. The results show that the fatigue crack generally initiated in the surface or near the surface of the sample area, such as hole and inclusion. The crack propagation regions under high stress amplitude was characterized by furrow and hollow, and obviously presented fine ripple vein. While lots of fatigue striations and sidesteps with the holes and secondary cracks generated in the crack propagation regions of low stress amplitude. Fatigue transient breaking area is a mixed fracture of brittle and ductile fracture. In the fatigue crack propagation stage, with the increasing of cycle times, secondary cracks gradually merged into primary crack on the path of crack propagation. The dislocation of crack tip,grain boundaries and different grain orientations have great influence on the path of crack growth, which can make cracks bending.

Fatigue Properties of Casting TC4 Alloys Treated by Hot Isostatic Pressing

2011 ◽  
Vol 197-198 ◽  
pp. 1668-1673
Author(s):  
Yu Hong Yao ◽  
Xiao Feng Shangguan ◽  
Jiang Nan Liu ◽  
Zheng Pin Wang ◽  
Jian Feng Wei
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Growth Rates ◽  
Stress Ratio ◽  
Fatigue Properties ◽  
Stress Ratios ◽  
Crack Growth Rates

With the aircraft structure design criterion from traditional static strength design to damage tolerance design and with the independent research and development of new-type civil turbofan regional aircraft and the implement of the plan to develop the country's own large passenger jets in China, it is essential to do some researches on casting TC4 alloys for the lack of the data of fatigue properties. The detail fatigue rating cut-off (DFRcutoff) values of casting TC4 alloys are measured and calculated by double dots method, the thresholds in fatigue crack propagation and the fatigue crack growth rates at different stress ratios are studied and the fatigue fracture at different stress ratios are observed by scanning electron microscopy. The results show that DFRcutoff value by double-dot method is 375.83 Mpa. The thresholds of fatigue crack propagation decrease with the increase of the stress ratio, whereas the fatigue crack growth rates increase with the increment of the stress ratio and the relationship curves between fatigue crack propagation rates and the stress intensity factor range have been obtained. Moreover, SEM observations indicate that the fatigue trips become wide with the increasing of the stress ratio.

Fatigue Properties for Micro-Sized Ni-P Amorphous Alloy Specimens

1999 ◽  
Vol 605 ◽  
Author(s):  
S. Maekawa ◽  
K. Takashima ◽  
M. Shimojo ◽  
Y Higo ◽  
M. V Swain
Keyword(s):  
Fatigue Crack ◽  
Amorphous Alloy ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Stress Ratio ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Stress Intensity Factor Range ◽  
Fatigue Crack Propagation Rate ◽  
Stress Ratios

AbstractFatigue crack propagation tests at different stress ratios of 0.1 and 0.5 have been performed on microsized Ni-P amorphous alloy specimens to investigate the influence of stress ratio in the crack growth properties of microsized materials. The specimens tested were cantileverbeam-type with dimensions of 10 × 12 × 50 νm3 prepared by focused ion beam machining. Notches with a depth of 3 [m were introduced in all specimens. The entire set of fatigue tests as performed using a newly developed fatigue testing machine in air at room temperature. Fine stripes deduced to be striations were observed on the fatigue fracture surface. Careful measurements of the striation spacings were made. Fatigue crack propagation rate, that is striation spacing, is plotted as a function stress intensity factor range. Fatigue crack propagation rate at stress-ratios of 0.1 and 0.5 in microsized Ni-P amorphous alloy specimens are given by da/dN ∼ 1.3 × 10−8 ΔK;1.16 and da/dN ∼ 3.7 × 10−8 ΔK0.5, respectively. At a given ΔK, crack propagation rate at a stress ratio of 0.5 was higher than that at 0.1. It is considered that a decrease in crack propagation rate at stress ratio of 0.1 is due to adecrease in effective stress intensity factor range ΔKeff, by the effect of crack closure.

scholarly journals Effects of Shot-Peening and Stress Ratio on the Fatigue Crack Propagation of AL 7475-T7351 Specimens

2018 ◽  
Author(s):  
Natália Ferreira ◽  
Pedro Antunes ◽  
José A. M. Ferreira ◽  
José D. M. Costa ◽  
Carlos Capela
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Shot Peening ◽  
Stress Ratio ◽  
Stress Ratios ◽  
Crack Growth Rates ◽  
Hardness Values

Shot peening is an attractive technique for fatigue enhanced performance of metallic components, because it promotes crack initiation retardation and later crack growth. Engineering design based on fatigue crack propagation predictions applying the principles of fracture mechanics is commonly used in aluminum structures for aerospace engineering. The main purpose of present work was to analyze the effect of shot peening on the fatigue crack propagation of the 7475 aluminum alloy, under both constant amplitude loading and periodical overload blocks. The tests were performed on 4 and 8 mm thickness specimen's with stress ratios of 0.05 and 0.4. The analysis of the shot-peened surface showed a small increase of the micro-hardness values, due to the plastic deformations imposed by shot peening. The beneficial effect of surface peening on fatigue crack growth rates is quite limited to an increasing near the threshold. The specimens’ thickness has only marginal influence on the crack propagation, in opposite to the stress ratio. Periodic overload blocks of 300 cycles promotes a reduction of the fatigue crack growth rate for both intervals of 7,500 and 15,000 cycles.

Description of Small Fatigue Crack Propagation in ODS Steel

2014 ◽  
Vol 891-892 ◽  
pp. 911-916
Author(s):  
Pavel Hutař ◽  
Ivo Kuběna ◽  
Miroslav Šmíd ◽  
Martin Ševčík ◽  
Tomáš Kruml ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Fatigue Testing ◽  
Low Cycle Fatigue ◽  
High Stress ◽  
Oxide Dispersion Strengthened ◽  
Ods Steel ◽  
Small Fatigue Crack ◽  
Propagation Law

The oxide dispersion strengthened (ODS) steels are widely studied as possible candidate material for fission and fusion technology. Due to application of the ODS materials, mainly low cycle fatigue is important. Therefore, small crack initiation and propagation for rather high stress amplitude are in focus. The main aim of the presented work is description of the small fatigue crack propagation for ODS-EUROFER steel. Due to limited quantity of ODS steel special miniaturized cylindrical specimens for fatigue testing were designed. Crack propagation law based on plastic part of J-integral is presented and applied for mentioned material. The resulting fatigue crack propagation rates for ODS-EUROFER steel and EUROFER 97 are compared and discussed.

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