NASA-TN-D-5390-1969 Effect of stress ratio on fatigue-crack growth in 7075-T6 and 2024-T3 aluminum-alloy specimens《应力比对7075-T6和2024-T3铝合金样品疲劳裂缝扩展的影响》.pdf

1、NASAo_|ZI.,-,-ZTECHNICAL NOTE NASA TN D-5390EFFECTONINALUMINUM-ALLOYOF STRESS RATIOFATIGUE-CRACK GROWTH7075-T6 AND 2024-T3SPECIMENSby C. Michael HudsonLangley Research CenterLangley Station, Hampton, Va.NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. AUGUST 1969Provided by IHSNot for

2、 ResaleNo reproduction or networking permitted without license from IHS-,-,-,1Provided by IHS Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-1. Report No. 2. Government Accession No.NASA TN D-53904. Title and SubtitleEFFECTOF STRESSRATIO ON FATIGUE-CRACKGROWTHIN 7

3、075-T6AND 2024-T3ALUMINUM-ALLOYSPECIMENS3. Recipients Catalog No.Performing Organization Name and AddressNASA Langley Research CenterHampton, Va. 23365Sponsoring Agency Name and AddressNational Aeronautics and SpaceAdministrationWashington, D.C. 20546S. Report DateAugust19696. Performing Organizatio

4、n Code7. Author(s) 8. Performing Organization Report No.C. Michael Hudson L-66629. 10. Work Unit No.126-14-15-01-23111. Contract or Grant No.13. Type of Report and Period CoveredTechnical Note14. Sponsoring Agency Code15. Supplementary Notes16. AbstractAxial-load fatigue-crack-growthtests were condu

5、cted on 12-inch-wide (305-ram)sheet specimensmadeof 7075-T6and 2024-T3aluminum alloy. These tests were madeat stress ratios R (ratio of the minimumstress to the maximum stress) ranging from -1.0 to 0.8 and at maximum stress levels ranging from 5 to50 ksi (34 to 340 MN/m21 to study the effectsof stre

6、ss ratio on fatigue-crack growth.The experimental results were analyzed by using the stress-intensify method. For a given positivestress ratio, the fatigue-crack-growthrate was a single-valued function of the stress-intensity range forboth 7075-T6and 2024-T3aluminum alloys. For R - 0 the crack-growt

7、h rates varied systematically with Rfor both materials; the higher stress ratios produced higher rates of fatigue-crack growth for a given stress-intensity range.Fatigue cracks in the 7075-T6aluminum alloy grew at the same rates in all tests with R - 0the crack-growth rates varied systematically wit

8、h R for both materials; the higherstress ratios produced higher rates of fatigue-crack growth for a given stress-intensityrange.Fatigue cracks in the 7075-T6 aluminum alloy grew at the same rates in all testswith R -0.- The fatigue-crack-growth data from the tests with R = 0 arepresented in figure 3

9、 as plots of rate as a function of the stress-intensity range Ak.For a given positive stress ratio, rate was a single-valued function of Ak for both7075-T6 and 2024-T3 alloys. Crack-growth rates varied systematically with R forboth materials; the higher stress ratios produced higher rates of fatigue

10、-crack growthfor a given value of Ak.Data for R =_-0.Rote,nm/cy cle19Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-.z 0I0idsin./cycle165io-+D I0 0I0005 I0Ak,MN/m 3/220I3OIA/OOOSymbolO0R00.330.50.7i I15 20Ak,ksi-in I/225I3O(b) _24-T3 alloy.Figure3.-

11、 Concruded.4OI5-I04I0Rote,nm/cycle,d200I3520Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Rate,in./cycle10-110-210-310-4-51010-6I0A kj MN/m3/220 3O 4OI ! e |80oo00o o0o oo o000 0006-I05-I04o! I I I i I J5 10 15 20 25 30 35-I03I02I0Ak, ksi-in 1/2Fig

12、ure 4.- Variation of fatigue-crack-growth rate with Ak for R 0 in 7075-T6 alloy.Rate,nm/cycle21Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-3i0-4I0Rote,in./cycleid 515s-I0IL_k,MN/m 3/220!3OIIIIIt IIklaQ/0SSymbolDLoading frequency30cpm (0.5 Hz)820

13、cpm(13.7 Hz)(_7 0 I ! i | i I I 5 I0 15 20 25 30 35_k,ksi-in i/240!5-I04I0Rate,nm/cycle3I02-I0I0Figure 5.- Variation of fatigue-crack-growth rate with 6k for R = -1 in 2024-T3 alloy. (Data are for two loading frequencies.)22Provided by IHSNot for ResaleNo reproduction or networking permitted without

14、 license from IHS-,-,-ld3jO “4Rate,in./cycleio-5io-6Llk, MN/m 3/2I0 20 30 40I I I 1QDQr_Qr_O _aa 0s_ g- _ o%a _aOG_( _ SymboloOo0000(3t3t_m0000Rm-I00-7 i I i I I I JI0 0 5 I0 15 20 25 30 355-I04I0Rate,n m/cycle,d2-IO-I0Ak, ksi-in 1/2Figure 6.- Variation of fatigue-crack-growthrate with Ak for R = 0

15、and R = -1 in 2024-T3alloy.23Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-iO-I10 -2iO -_Role,in./cycle10 -4iO -510 -6iO -I10 -2i0 -_Rate,in./cycle10 .4iO -5Ak ,MN/m 3s2I0 20 30 4o o0 OR_O oo00OR=O.5Ak ,MN/m 3/2_o 29 30 40 OA k,M N/m 3/z,o zo _oR=0

16、.33 /AAiR=0.7 R-O.Bi I i I-o s ,o ,5 20 _s 3o _:so-_-% ,s 2o 25 so sso s ,o is 20 J5 3o _5Ak, ksi-in _/2 Ak,ksi-in w2 Ak, ksi-in V2(a) 7075-T6 alloy.Figure l.- Correlation of experimental fatigue-crack-growth rates at various stress ratios with Formans equation (ref. 2).40lo,o5Role,nm/cyciei3I0,d,o“

17、io_Rolenm/cyc e,o“,o3,o24Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-10-3Id“Rate,in./cycleId _Id“Rate,in./cycleiO-5Ak,M N/rn 3/2IO 20 30 400R=O ooiR=O.5Ak,MN/m 3/zIO 20, iR=0.33I I I I I IR =0.7,oRate,nm/cycle(b) 2024-T3alloy.Figure 7.- Concluded

18、.03,O_IOI II0 15 20 25 30 35Ak,ksi-inii,o_Rate,nm/cycleio_IO25Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-iO-IIO-2iO-_Rote,in. / cycl_iO-_IO-“,Ak ,MNlrn 3/2I0 20 30o oR_Oo_ oErdog ans equation -_-IOIO-I1i0“_ I R = O. 5| o i0-_ oRote, _ _in/cycle1

19、0-410-5i/Id60 5 I0 15 20 25Ak,ksi-in V2400Ak ,MN/m 3/zI0 20 3OR=O2OOR=0.75 IO 1_5- 2_OAk,ksi-in I/240 0 I0/k k, MN/m 3/220R=O.3330R=O.84O6IO3;0 35 0 25 3_0 35 0 30 355 IO 15 20 25A k,ksi-in I/25I0Rote,nm/cycle4I0(a) 7075-T6 alloy.Figure 8.- Correlation of experimental fatigue-crack-growth rates at various stress ratios with Erdogans equation (ref. 3).3IO2IO6IO5IORate,nm / cycle4IOio2IO26Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-