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.

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.

Effect of Environment on Fatigue Crack Propagation Behavior of an Al-Cu-Mg Aluminum Alloy

2014 ◽  
Vol 1004-1005 ◽  
pp. 142-147
Author(s):  
Ming Liu ◽  
Kun Zhang ◽  
Sheng Long Dai ◽  
Guo Ai Li ◽  
Min Hao ◽  
...  
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Fatigue Crack Growth Rate ◽  
Fatigue Crack Propagation Behavior ◽  
Stress Ratios

The fatigue crack propagation behaviors of an Al-Cu-Mg alloy are investigated in different environments and with varying stress ratios. Fatigue experiments are carried out via a fatigue crack growth rate test in laboratory air, a 3.5% (mass fraction) NaCl solution and a tank seeper. The results show that a corrosion environment has an obvious influence on the fatigue crack growth rate, and the degrees of influence of the two different corrosive environments are basically identical. When the stress ratio is R = 0.5 and 0.06 with a decrease of the stress intensity factor, the difference in the crack propagation rates for the corrosion and air environments gradually increases. However, the corrosion acceleration in each stage of crack propagation is obvious while R=−1.

Study on Fatigue Crack Propagation at Negative Stress Ratio in 2A12 Aluminum Alloy

2011 ◽  
Vol 335-336 ◽  
pp. 809-812
Author(s):  
Shi Gang Bai ◽  
Jia Zhen Zhang ◽  
Yu Sha
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Stress Ratio ◽  
Compressive Loading ◽  
Stress Cycle ◽  
Made In

This paper intends to get compressive loading effect on fatigue crack growth of 2A12 aluminum alloy. The fatigue crack propagation tests at negative stress ratio R=-0.5, -1and -2 were made in different applied compressive loading. The result showed that the effect of the compressive loading part of the applied stress cycle on fatigue crack growth rate in 2A12 aluminum alloy at negative stress ratio can not be omitted.

Transient Fatigue Crack-Growth Behavior and Damage Zones in Zr-Based Bulk Metallic Glass

2003 ◽  
Vol 806 ◽  
Author(s):  
Peter A. Hess ◽  
Reinhold H. Dauskardt
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Crack Closure ◽  
Growth Rates ◽  
Fatigue Loading ◽  
Structural Applications ◽  
Crack Growth Rates

ABSTRACTFatigue crack propagation mechanisms of bulk metallic glasses (BMGs) are not well understood, limiting their use in safety-critical structural applications particularly where complex fatigue loading may occur. Accordingly, the present study examines the effects of variable amplitude fatigue loading associated with block loading and tensile overloads on fatigue crack-growth rates in a Zr-based BMG. Crack growth studies were conducted on compact tension specimens using computer control of the applied stress intensity range, ΔK. Fatigue crack closure loads, which represent the initial contact of mating crack surfaces during the unloading cycle, were continuously monitored during testing. Abrupt drops in ΔK were found to significantly decrease fatigue crack-growth rates far below equilibrium values, arresting growth completely at a ΔK twice the nominal fatigue threshold ΔKTH. Conversely, an abrupt increase in ΔK was found to accelerate fatigue crack-growth rates. The effects of roughness-induced crack closure were assessed and found to be consistent with the suppression or acceleration of growth rates. However, in order to fully explain the observed transient growth rate response, other mechanisms that may be related to the fatigue mechanism itself were also considered. Specifically, the nature of the fatigue crack tip damage zone was also investigated. As BMGs lack distributed plasticity at low temperatures, the plastic zone differs greatly from that seen in ductile crystalline materials, and its role in fatigue crack propagation mechanisms is examined.

Definition of Fatigue Crack Growth Thresholds for Ferritic Steels in Fitness-for-Service Codes

2018 ◽  
Author(s):  
Kunio Hasegawa ◽  
Bohumir Strnadel
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Stress Ratio ◽  
Fatigue Tests ◽  
Ferritic Steels ◽  
Stress Ratios ◽  
Definition Of ◽  
Crack Growth Rates

Fatigue crack growth rates are expressed as a function of the stress intensity factor ranges. The fatigue crack growth thresholds are important characteristics of fatigue crack growth assessment for the integrity of structural components. Almost all materials used in these fatigue tests are ferritic steels. As a result, the reference fatigue crack growth rates and the fatigue crack growth thresholds for ferritic steels were established as rules and they were provided by many fitness-for-service (FFS) codes. However, the thresholds are not well defined in the range of negative stress ratio. There are two types of thresholds under the negative stress ratio. That is, constant thresholds and increment of thresholds with decreasing stress ratios. The objective of this paper is to introduce the thresholds provided by FFS codes and to analyze the thresholds using crack closure. In addition, based on the experimental data, definition of the threshold is discussed to apply to FFS codes. Finally, threshold for ferritic steels under the entirely condition of stress ratio is proposed to the ASME Code Section XI.

Fatigue-Crack Propagation in Steels of Various Yield Strengths

1971 ◽  
Vol 93 (4) ◽  
pp. 1190-1196 ◽  
Author(s):  
J. M. Barsom
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Growth Rates ◽  
Structural Steels ◽  
Martensitic Steels ◽  
The Relationship ◽  
Crack Growth Rates

The useful life of highly constrained welded structures subjected to cyclic loads often depends on the crack-propagation behavior of the material. Thus, to predict the service life of many structures and to establish safe inspection intervals, an understanding of the rate of fatigue-crack propagation in steel is required. Accordingly, an investigation was conducted to determine the fatigue-crack-growth rates in structural steels ranging in yield strength from 36 to 191 ksi; for this study, wedge-opening-loading (WOL) specimens were used. The tests were conducted at room temperature in an air environment, and the results were compared with published fatigue-crack-growth data for steels having similar yield strengths. The results showed that the primary factor affecting fatigue-crack-growth rates in structural steels is the applied stress-intensity-factor range, ΔKI, and that conservative estimates of fatigue-crack growth per cycle of loading, da/dN, for martensitic steels are obtained from the relationship dadN=0.66×10−8(ΔKI)2.25 where a is in inches and ΔKI is in ksi in. Similarly, the data showed that conservative estimates of da/dN for ferrite-pearlite steels are obtained from the relationship dadN=3.6×10−10(ΔKI)3 As indicated in these equations, the fatigue-crack-growth rates were higher for martensitic steels than for ferrite-pearlite steels. The data also showed that the fatigue-crack growth per cycle accelerated for all the steels, and that this transition from the above relationships to increased rates occurred when the crack-opening-displacement range, Δδ, which is a measure of the strain range at the crack tip, reaches a critical value. The fatigue-rate transition in martensitic steels occurred when Δδ was about 1.6 × 10−3 in. However, the fatigue-rate transition in ferrite-pearlite steels occurred at a Δδ value slightly higher than 1.6 × 10−3 in. A model based on micro structural considerations is presented, which accounts for these differences in the fatigue-crack-growth behavior between martensitic and ferrite-pearlite steels.

Fatigue Crack Propagation at Negative Stress Ratio in 2A12 Aluminum Alloy

2010 ◽  
Vol 146-147 ◽  
pp. 185-188 ◽  
Author(s):  
Yu Sha ◽  
Shi Gang Bai ◽  
Jia Zhen Zhang
Keyword(s):  
Growth Rate ◽  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Stress Ratio ◽  
Compressive Loading ◽  
Loading Effect

Fatigue crack propagation tests in the Paris region were performed in order to get compressive loading effect on fatigue crack growth at negative stress ratio (R) in 2A12 aluminum alloy. The results of the tests showed that the effect of the compressive loading part of the applied stress cycle on fatigue crack growth rate da/dN in 2A12 aluminum alloy at negative stress ratio can not be omitted. The fatigue crack growth rate at R<0 was more than that at R>0 under the same range of stress intensity factor Kmax. The da/dN is the function of Kmax and stress ratio R. The promoting effect has an increase trend with the increase of the absolute value of the negative stress ratio R. Then a model involved compressive loading effect on fatigue crack propagation at negative stress was obtained. The model has been obtained good agreements with the experimental data.

Analysis on Fatigue Crack Growth Rates Under a Wide Range of Stress Ratios

1986 ◽  
Vol 108 (2) ◽  
pp. 209-213 ◽  
Author(s):  
M. Kurihara ◽  
A. Katoh ◽  
M. Kawahara
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Stress Ratio ◽  
Crack Opening ◽  
Wide Range ◽  
Stress Ratios ◽  
Crack Opening Stress ◽  
Crack Growth Rates

In the present study, a series of fatigue crack growth tests were carried out in order to examine the effects of stress ratio R upon crack growth rates, together with the crack closure behaviors. Fatigue tests were conducted with center-notched specimens of two kinds of pressure vessel steels (500 MPa class and 800 MPa class) under cyclic axial loading in various stress ratios R ranging from −5 to +0.8. Crack opening stress levels were determined by the unloading elastic compliance method. An expression of fatigue crack growth rates under a wide range of stress ratios was proposed, taking into account the relationship between stress ratio R and crack opening stress ratio U. The crack growth behaviors near the threshold conditions were also discussed.

Fatigue Crack Growth in Flow Formed INCONEL 718

2016 ◽  
Vol 879 ◽  
pp. 374-379
Author(s):  
Costa Coleman ◽  
Martin R. Bache ◽  
Carl Boettcher
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Growth Rates ◽  
Inconel 718 ◽  
Longitudinal Direction ◽  
Test Pieces ◽  
Crack Growth Rates

Fatigue crack propagation has been measured in flow formed Inconel 718 (IN718). Test pieces were extracted from a flow formed tubular structure in the longitudinal direction, retaining the tube curvature across their width. Crack growth rates (da/dN) were measured at 20, 300, and 400oC. For comparison, tests were repeated on specimens with an identical geometry but machined from conventionally forged IN718. Detailed metallurgy of the flow formed material is presented.

Fatigue Crack Propagation in A533B Steels—Metallographic and Fractographic Analyses

1979 ◽  
Vol 101 (2) ◽  
pp. 155-164 ◽  
Author(s):  
A. D. Wilson
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Nonmetallic Inclusion ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Growth Rates ◽  
Electron Microscopic ◽  
Alloy Plate ◽  
Crack Growth Rates

Metallographic and fractographic analyses are performed on A533B low alloy plate steels made by three steelmaking practices. The fatigue crack growth rates of these steels had been previously established in all six possible testing orientations. By using quantitative image analysis to quantify the nonmetallic inclusion structures of these steels, graphical and statistical correlations were established between the two material constants of the fatigue crack growth rate equation and various inclusion parameters. The average area of an inclusion on the metallographic cross section corresponding to the plane of fracture was found to be the best single parameter for establishing a correlation applying to all testing orientations. Scanning electron microscopic investigations of the fracture surfaces of the fatigue crack propagation specimens indicated that the inclusions (Type II manganese sulfides and alumina galaxies) exerted a predominant effect on the fatigue crack propagation behavior. Both studies provide additional evidence that the differences in fatigue crack growth rates between and within the steels of this investigation can be a result of the nonmetallic inclusion structures of the materials.

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