1、- NASA TECHNICAL NOTE d 00 Ih c I n z NASA TN D-1584-ii I EVALUATION OF THE INFLUENCE OF LOAD RANDOMIZATION AND OF GROUND-AIR-GROUND CYCLES ON FATIGUE LIFE by Eugene C. Naumann Langley Research Center Langley Station, Hampton, Va. NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. OCTOB
2、ER 1964 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-ERRATA NASA Technical Note D-1584 EVALUATION OF THE IIWLUENCE OF LOAD RANDOMIZATION AND OF GROUND-AIR-GROUND CYCUS ON FATIGUE LIJQ By Eugene C. Nau“ y I- October 1964 (?,. I l*i /,? 6 L-, -I? ap
3、proximately 2:l and 1.25:l were obtained, respectively. Sufficient data are not available to establish reliable relationships between GAG cycle spacing and life. From this it appears that the number of gust cycles used to represent typical flight directly influences the results obtained when the num
4、ber of flights simulated is used as the basis of comparison. Thus, the life obtained in fatigue-evaluation tests can be very misleading if the anticipated service load history is appreciably different from the actual service load history. CONCLUSIONS 0 The results of variable-amplitude axial-load fa
5、tigue tests on edge notched spechens with loads programed to approximate a gust-load spectrum support the following conclusions: 1. The insertion of ground-air-ground cycles (GAG) produced a large decrease in the number of simulated flights when compared with similar tests without the ground-air-gro
6、und cycle. The.numberof flights simulated was found to be influenced as indicated by the following conditions: (a) GAG cycle range -number of flights decreased as GAG range increased the change is much Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
7、greater than anticipated by 1n/N) and (b) degree of load randomization - the decrease in number of flights was greater in random tests than in block tests having GAG cycles with the same range. 2. Ground-air-ground cycle spacing has a definite influence on the fatigue life as measured by the number
8、of flights simulated, whereas no effect was noted on the basis of summation of cycle ratios 3. In tests using random-load sequences, the degree of load randomization present influences the fatigue life; life increases as the degree of the random ization increases. 4. The omission of the lowest load
9、level did not significantly affect the number of flights simulated for tests in which the GAG cycle was introduced. 5. All the trends noted herein can be explained qualitatively by using the concepts of residual stresses and residual-static strength. Langley Research Center, National Aeronautics and
10、 Space Administration, Langley Station, Hampton, Va., July 9, 1964. 20 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-APPENDIX CONVERSION OF U.S. CUSTOMARY UNITS TO SI UNITS The International System of Units (SI) was adopted by the Eleventh General
11、Conference on Weights and Measures, Paris, October 1960, in Resolution No. 12 (ref. 4). Conversion factors required for units used herein are: Length: inches X 0.0254 = Meters (m) Force: pounds X 4.4482216 = Newtons (N) Time: minutes x 60 = Seconds (s) Frequency: cps = Hertz (Hz) Prefixes to indicat
12、e multiples of units are: 106 mega (M) 10-3 milli (m) 21 I Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-REFERENCES 1. Naumann, Eugene C.; Hardrath, Herbert F.; and Guthrie, David E. : Axial-Load Fatigue Tests of 2024-T3and TOE-6 Aluminum-Alloy She
13、et Specimens Under Constant- and Variable-Amplitude Loads. NASA TN D-212, 1959. 2. Naumann, Eugene C.; and Schott, Russell L.: Axial-Load Fatigue Tests Using Loading Schedules Based on Maneuver-Load Statistics. NASA TN D-1253, 1962. 3. Naumann, Eugene C.: Variable-Amplitude Fatigue Tests With Partic
14、ular Attention to the Effects of High and Low Loads. NASA TN D-1522, 1962. 4. Anon.: International System of Units, Resolution No. 12. NASA TT F-200,1964. 5. Neuber, Heinz: Theory of Notch Stresses: Principles for Exact Stress Cal culation. J. W. Edwards (Ann Arbor, Mich.), 1946. 6. Grover, H. J.; B
15、ishop, S. Mj and Jackson, L. R.: Fatigue Strengths of Air craft Materials. Axial-Load Fatigue Tests on Unnotched Sheet Specimens of 24S-T3and 75s-6 Aluminum Alloys and of SAE 4130 Steel. NACA TN 2324, 1951. 7. Grover, H. J.; Hyler, W. S.; Kuhn, Paul; Landers, Charles B.; and Howell, F. M.: Axial-Loa
16、d Fatigue Properties of 24s-T and 75s-TAluminum Alloy as Determined in Several Laboratories. NACA Rep. 1190, 1954. (Supersedes NACA TN 2928.) 8. %ode, Richard V.; and Donely, Philip: Frequency of Occurrence of Atmos pheric Gusts and of Related Loads on Airplane Structures. NACA WR L-121,1944. (Forme
17、rly NACA ARR LkI2l. ) 9. Taussky, Olga; and Todd, John: Generation and Testing of Pseudo-Random Numbers. Symposium on Monte Carlo Methods, John Wiley and Copp, Martin R.: Summary of VGH and V-G Data Obtained From Piston-Engine Transport Airplanes From 1947 to 1958. NASA TN G29, 1959. 11. Anon.: A Te
18、ntative Guide for Fatigue Testing and the Statistical Analysis of Fatigue Data. Special Tech. Pub. No. 9l-A, ASTM, 1958. 12. McEvily, Arthur J., Jr.; Illg, Walter; and Hardrath, Herbert F. : Static Strength of Aluminum-Alloy Specimens Containing Fatigue Cracks. NACA TN 3816, 1956. 13. Hudson, C. Mic
19、hael; and Hardrath, Herbert F.: Investigation of the Effects of Variable-Amplitude Loadings on Fatigue Crack Propagation Patterns. NASA Tm D-1803,1963. 22 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-TABLE I.- TENSIIX PROPERTIES OF ALUMINUM-ALLOY.
20、MATERIALS TESTEB Eats from ref. 73 7075-T6 (152 tests) Property Average Minimum Yield stress (0.2-percent off set) -Inksi. . 75 *50 71 54 In W/m2 . 520.2 492.9 Ultimate tensile strength -Inksi 82.94 In m/m2 . 5719 5 Total elongation (2-inch (5.08-cm) gage length), percent 12.3 2024-T3 (147 tests) Yi
21、eld stress (0.2-percent offset) -Inksi 46.88 In W/m2 . 323 0 Ultimate tensile strength -Inksi. . 72.14 70.27 In m/m2 . 497.0 484.2 Total elongation (2-inch(5.08-cm) gage length), percent 21.6 1 15.0 Maximum 79 - 79 549.8 84.34 582*5 15.0 59.28 408.4 73.44 506.0 25.0 Provided by IHSNot for ResaleNo r
22、eproduction or networking permitted without license from IHS-,-,-TABLE 11.- VARIABLEAMPLITUDE LOAD PROGRAMS APPROXIMATING A GUST-LOAD HISTORY 7075-T6 aluminum-alloy specimens; Slg = 20 ksi (137.8 MN/m2) Load level Representative stress .-ksi m/m2 Relative frequency, cycles n/N per cycle 21.5 148.4 4
23、2.000 0 25.3 174.6 28.7 198.0 32.6 224.9 7,5001,190 175 .00000625 .00006024 .00017241 36.3 250.5 23 .00034482 40.1 276 9 7 2.5 .00067120 43.9 302.9 *5 .00122000 47.5 327.8 .I .00208000 RGAG = 0; GAG cycle Sig to 0 (20 ksi to 0) (137.8 m/m2 to 0) . . . . . . . . . . . . . . . . . .00002000 RGAG = -1/
24、2; GAG cycle SIg to -1/2Slg (20 ksi to -10ksi) (137.8 m/m2 to -68.9 MN/m2). . . . . . . . .00006293 2024-T3 aluminum-alloy specimens; Slg = 17.4 ksi (119.9 MN/m2) - 19.5 134.4 82, ooo 0 22.5 155 0 15, ooo .00000111 25.6 176.4 2,800 .00001370 28.7 197.7 350 .00005411 31.9 219.8 46 .00015391 35 -1 241
25、.8 7.4 .00036216 38.4 264.6 1.6 .00075500 41.5 285 9 35 .00013314 %AG = -1/2; GAG cycle Sig to -1/2Slg (17.4 ksi to -8.7 ksi) (119.9 MN/m2 to -59.9 MN/m2) . . . . . . . .00002325 -.- . .- . . 24 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-TABLE 1
26、11.- RESULTS OF CONSTANT-AMPLITUDE FATIGUE TESTS Specimen Geometric Life, cycles 53,00052, ooo 49,000 40,000 39,00030, ooo mean . . . 43,000 I (b) 7075-T6 aluminum alloy hean= 5 ksi (34.4 MN/m2); -. Specimen B93N2-6 B93N2-1 862-8 862-3 B103N2-7 Geometric mean %a = 20 ksi (137.8 MN/m2U Life, cycles 2
27、0,570 15,650 15,530 15, 090 13,430 . . . 15,890 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-t TABLE IV.- RESULTS OF VARIABLE-AMPLITUDE FATIGUE TESTS ON 7075-T6 ALUMINUM-ALLOY SPECIMEN Elg = 20 ksi (137.8 MN/m2fl (a) Block tests to evaluate possib
28、le machine difference at failure cycles Flights _.-Semiautomatic loading; step 1 omitted; reference 3 B11ON1- 1 142,120 2.54 11,843 B103N1- 9 125,690 2.36 10,474 BllON1- 2 121,450 2.20 10,121 1031-B1OlNl-2 99,170-2Ii.2z 1.85 1.71 8,2648,115 Geometric mean . . . . . . . . 115,700 2.09 9,641 -_ B103N1
29、-3 114,450 1.98 9,5372 Automatic loading; same as reference 3 . -. . _ 1322-6 4 140,900 2.54 11,742 B126N2-4 2 123,035 2.21 10,2531042-5 7 115,759 2.10 9,647B124N2-5 7 115,759 2.10 9,6471372-6 6 115,560 2.06 9,630B13lN2-5 3 115,111 2.01 2x223 Geometric mean . 120,600 2.15 io, 058 26 Provided by IHSN
30、ot for ResaleNo reproduction or networking permitted without license from IHS-,-,-TABLE IT.- RESULTS OF VARIABLE-AMPLITUDE FATIGUE TESTS ON 7075-T6 “UM-ALLOY SPECIMEN - Continued -(b) Random cycle tests to evaluate randomness of random sequence generation method* Specimen Flights Start at card 1 B9N
31、2-3 122-3 92 6 82-5 B14N2-7 B9N2-9 Geometric mean . . Start at B129N2-5 5 BM-7 4 1322-10 51292-10 4 1282-1 5B9N2-7 5102-3 6 Geometric mean . . . . . . . . . . . . Start at Geometric mean . . . . . . . . . . . . Start at -B42-9 6 BlN2-1 4 82-9 4 B42-6 782-9 7su2-9 4 19,89019,55015,23213,49812,41012,3
32、76 0.43 .42 .33 * 29 .27 3 1,5151,4891,162 1,031945 -2% 15,170 0.33 1,158 card 500 19,78819,31219,10815,47015,30013,97413,498 0.43 .42 .42 .34 .33 .30 2.2 1,4981,466 1,4511,1731,160 1,0571,023 16,450 0.36 1,256 card 1000 17,63114,926 1,3691,122 14,75614,75614,75614,722 1,1091,109 1,log1,108 15,225 1,162 card 1500 20,842 20,196 18,25814,21214,212 13,940 1,5921,5441,394 1, 087 1,0871,066 Geometric mean . . . . . . . . . . . . 16,670 1,272 * Highest load level occurs on card 1435. 27 I Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
