Fatigue Crack-growth and Crack Closure Behavior of Aluminum Alloy 7050 and 9310 Steel Over a Wide Range in Load Ratios Using Compression Pre-cracking Test Methods PDF Download
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Author: Talal Mehdi Senhaji
Publisher:
ISBN:
Category :
Languages : en
Pages : 58
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Book Description
Fatigue-crack-growth-rate tests were conducted on compact tension specimens made of 7050-T7451 aluminum alloy and 9310 steel. Compact tension specimens were tested over a wide range of load ratios (0.1 ≤ R ≤ 0.9) to generate crack-growth-rate data from threshold to near fracture. Three methods were used to generate near threshold data. A crack-closure analysis was performed on both materials using the FASTRAN crack-closure model. The crack-growth-rate data for each material correlated very well and each collapsed onto a nearly unique curve in the low- and mid-rate regimes using the strip-yield model in the FASTRAN life-prediction code. For the 7050 alloy, a constraint factor of a = 1.8 was required, while for the 9310 steel a = 2.5 worked very well in correlating the test data over a very wide range in R values and rates from threshold to near fracture.
Author: Talal Mehdi Senhaji
Publisher:
ISBN:
Category :
Languages : en
Pages : 58
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Book Description
Fatigue-crack-growth-rate tests were conducted on compact tension specimens made of 7050-T7451 aluminum alloy and 9310 steel. Compact tension specimens were tested over a wide range of load ratios (0.1 ≤ R ≤ 0.9) to generate crack-growth-rate data from threshold to near fracture. Three methods were used to generate near threshold data. A crack-closure analysis was performed on both materials using the FASTRAN crack-closure model. The crack-growth-rate data for each material correlated very well and each collapsed onto a nearly unique curve in the low- and mid-rate regimes using the strip-yield model in the FASTRAN life-prediction code. For the 7050 alloy, a constraint factor of a = 1.8 was required, while for the 9310 steel a = 2.5 worked very well in correlating the test data over a very wide range in R values and rates from threshold to near fracture.
Author: J. C. Newman
Publisher:
ISBN:
Category : Crack closure
Languages : en
Pages : 16
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Author:
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ISBN:
Category :
Languages : en
Pages : 12
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Book Description
Author: John J. Ruschau
Publisher:
ISBN:
Category : Aluminum
Languages : en
Pages : 15
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Book Description
The scope of this paper is to determine the fatigue-crack growth rates in the near-threshold regime for both an aluminum and titanium alloy using the compression precracking constant-amplitude (CPCA) test method on compact specimens. Tests were conducted over a wide range of stress ratios (R=Pmin/Pmax=0.1 to 0.9). Results were compared with threshold and near-threshold data generated on the same materials using the ASTM E647, "Standard Test Method for Measurement of Fatigue Crack Growth Rates," load-shedding test procedure. On the 7075-T651 alloy, very little difference was observed in threshold values between the load-shedding and CPCA test methods. In contrast, the titanium alloy (Ti-6Al-4V) showed very large differences between the CPCA and load-shedding test results in the near-threshold and threshold regimes for the low stress ratios. Results under high R conditions (R>=0.7) agreed well between the two-threshold test methods for both materials. On the titanium alloy, the load-shedding test method also produced a specimen width effect on near-threshold behavior, whereas the CPCA test method produced results that were independent of specimen width and produced "steady-state" constant-amplitude data in the near-threshold regime, after the crack had grown several compressive plastic-zone sizes.
Author: KK. Chan
Publisher:
ISBN:
Category : Aluminum forging
Languages : en
Pages : 19
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Book Description
The crack-opening stress was measured using a strain gage technique on 7050 aluminum alloy, under constant amplitude and repeated overload. The behavior of crack-opening stress predicted by Newman's FASTRAN-II is consistent with the experimental results for repeated overload. It is also found that the FASTRAN-II program is capable of predicting crack growth on the 7050-T76 aluminum plate and 7050-T7452 aluminum hand forging under complex simulated flight loading which contains a significant number of compression cycles.
Author: J. C. Newman (Jr)
Publisher:
ISBN:
Category :
Languages : en
Pages : 52
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Author: DK. Chen
Publisher:
ISBN:
Category : Aluminum alloys
Languages : en
Pages : 14
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Book Description
Modified pre-cracked compact specimens of 2024-T3 and 7075-T6 aluminum alloys were subjected to four different overload patterns followed by subsequent constant-amplitude steady-state loading with R=Plmin/lmax equal to 0, -1/2, -1, and -2. The overload patterns were tension, compression-tension, tension-compression, and compression. Cyclic loading with negative stress ratio, R, drastically reduced crack-growth retardation. The higher the negative R ratio the greater the reduction in retardation. Overload ratios, OLR =Phmax/Plmax, ranging from 2.0 to 3.0 were used. For compression overloads, the OLR ranged from -2.0 to -4.0. High compression overloading was detrimental and dependent upon subsequent R ratio loading. Substantial fracture surface abrasion near the mid-thickness occurred for higher negative R ratios. Striations were not readily found in this region, however, they were quite evident near the edges, which indicated crack closure was greater near the mid-thickness. The 2024-T3 gave better crack growth life than 7075-T6 in some loading conditions, while the opposite was true for other loadings. The results indicate negative R ratio must be considered in retardation models and that retardation life cannot be modeled based solely on overload plastic zone sizes.
Author: Rodney L. Wilkinson
Publisher:
ISBN:
Category : Aluminum alloys
Languages : en
Pages : 68
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Book Description
Changes in the crack growth behavior of 7075-T651 aluminum specimens which has been exposed to temperatures between 150 degrees and 355 degrees F (66 deg and 179 deg C) were evaluated. Specimens were fatigue tested at room temperature under flight-by-flight loading conditions. Results from these tests were then compared with data from the baseline (as received) material. Exposure to 250 deg F (121 deg C) or more produced a definite increase in speciment life, apparently due to a decrease in crack growth rates.
Author: William T. Riddell
Publisher:
ISBN:
Category : Aluminum alloys
Languages : en
Pages : 24
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Author: EP. Phillips
Publisher:
ISBN:
Category : Aluminum alloys
Languages : en
Pages : 11
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Book Description
Crack opening loads were determined in load-shedding fatigue crack growth threshold tests on 2024-T3 aluminum alloy at stress ratios R of -2, -1, 0, 0.33, 0.5, and 0.7. The effects of load-shedding procedure and rate were investigated. Values of threshold ?K were found to vary significantly with R, whereas values of threshold effective ?K did not. That is, the variation of threshold ?K with R was almost completely explained by accounting for the measured variation in crack opening load behavior with R. The load-shedding guidelines of ASTM Test Method for Measurement of Fatigue Crack Growth (E 647) produced a threshold ?K value for R = 0.7 that was in agreement with the value determined using a procedure that should minimize closure effects (constant-Kmax, increasing-Kmin test). At both R = 0 and R = 0.7, high load-shedding rates produced high values of threshold ?K caused by large closure effects.
