1、NASA TECHNICAL NOTE v cr) cr) N ti z c NASA TN D-2331 - FATIGUE-CRACK PROPAGATION IN SEVERAL TITANIUM AND AND ONE SUPERALLOY STAINLESS-STEEL ALLOYS Langley Research Center Langley Station, Hampton, Va. + NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. OCTOBER 1964 5 Provided by IHSNo
2、t for ResaleNo reproduction or networking permitted without license from IHS-,-,-1 TECH LIBRARY KAFB, NM I Illill Ill11 111ll lllll I1ll1 Mll11111111 0077545 FATIGUE-CRACK PROPAGATION IN SEVERAL TITANIUM AND STAINLESS-STEEL ALLOYS AND ONE SUPERALLOY By C. Michael Hudson Langley Research Center Langl
3、ey Station, Hampton, Va. NATIONAL AERONAUTICS AND SPACE ADMINISTRATION _ For sale by the Office of Technical Services, Deportment of Commerce, Woshington, D.C. 20230 - Price $0.75 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-FATIGUE-CRACK PROPAGAT
4、ION IN SENERAL TITANIUM AND STAINLESS-STEEL ALLOYS AND ONE SUPERALLOY By C. Michael Hudson SUMMARY Axial-load fatigue-crack-propagation tests were conducted on 8-inch-wide (20.3-cm) sheet specimens made of Ti-4Al-Po-lV (Aged), Ti-6U-4V (Annealed) , and Ti-8Al-lMo-lV (Triplex Annealed) titanium alloy
5、s, AM 350 (20-percent CRT) , AM 350 (Double Aged), PH 14-8Mo (SRH 950), PH 15-7Mo (TH 1050), and AIS1 301 (50-percent CR) stainless steels, and Rene 41 (Condition B). Tests were run at 800 F (300 K), 50 F (5610 K), and, in some cases, -logo F (195O K) to deter- mine the effect of temperature on the
6、fatigue-crack-propagation characteristics a of each material. The materials are ranked according to their resistance to fatigue-crack propagation, and Ti-8Al-lMo-lV (Triplex Annealed) appeared to be the most resist- ant over the temperature range of the investigation. Special apparatus developed for
7、 the elevated- and cryogenic-temperature studies are described herein. INTRODUCTION The elevated temperatures associated with aircraft flying at a Mach number of approximately 2.5 and faster precludes the use of aluminum alloys for struc- tural components. Consequently, aircraft designers must turn
8、to more heat- resistant materials with which they have had little aircraft-design experience. Important to the selection of these materials is their resistance to fatigue- crack propagation and the effect of temperature on this resistance. Designers know that fatigue cracks will probably form in the
9、ir aircraft structures, and consequently they must select materials having high resistance to crack growth in order to minimize the danger of fatigue failure. An investigation has been undertaken to evaluate the crack-propagation char- acteristics of nine materials suitable for use at elevated tempe
10、ratures. This investigation included tests of the nine materials at room temperature of 80 F (300 K) and at elevated temperature of 550 (SIo K) . the effects of temperature on fatigue-crack growth, two of the materials were To evaluate further Provided by IHSNot for ResaleNo reproduction or networki
11、ng permitted without license from IHS-,-,-tested at the cryogenic temperature of -109 F (195 K). ducted at positive mean stresses on sheet specimens made of five stainless steels, three titanium alloys, and one superalloy. Tests have been con- The present paper presents the experimental results of t
12、his study. Included are effects of temperature on crack propagation in each material and a relative ranking of each material with respect to resistance to crack growth at each test temperature. All physical properties in this paper are given in both U.S. Customary Units and the International System
13、of Units. An appendix is included to explain the relationship between the two systems. E Youngs modulus, ksi or giganewtons/meter2 ( GN/m2) e total elongation in 2-inch- (3.08-cm) gage length, percent N number of cycles R ratio of minimum stress to maximum stress Sa s, 0, aY X one-half of total leng
14、th of central symmetrical crack, inches or alternating stress amplitude, ksi or meganewtons/meter2 ( MN/m2 ) mean stress, ksi or meganewtons/meter* (MI?/m2) ultimate tensile strength, ksi or meganewtons/meter2 ( MN/m2) yield strength (0.2-percent off set), ksi or meganewtons/meter2 (MN/m2) centimete
15、rs (cm) SPECIMENS AND TESTS Specimens The five stainless steels, three titanium alloys, and one superalloy studied in this investigation are listed as follows: AIS1 301 (50-percent Cold Rolled - eR) AM 350 (20-percent Cold Rolled and Tempered - CRT) AM 350 (Double Aged - DA) PH 15-“0 (TH 1050) 2 Pro
16、vided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-PH 14-8Mo (SFB 950) Re consequently, the cutting proc- ess was believed to have little effect upon the material surrounding the notch. The heat gener- A reference grid (fig. 2) was photographically printed
17、 on the surface of the specimen to mark intervals in the path of the crack. This reference grid Figure 2.- Grid used to mark intervals in crack path. 6 Notch LCen t ral L-63-4299.1 Grid spacing is 0.05 in. (1.27 mm). afforded ready observation of the crack front and provided a crack-growth path free
18、 of mechanical defects which might affect normal crack propagation. adopting the photographic reference grid, it was determined by metallographic examinations and tensile tests on specimens bearing the grid that the grid had no detrimental effects upon the materials at 550 F (561O K). Before Testing
19、 Equipment Axial-load fatigue-testing equipment used in this investigation included a subresonant machine, a hydraulic machine, and a combination hydraulic and sub- resonant machine. The subresonant machine had an operating frequency of 1800 cpm, a load capacity of ?20,000 pounds (+89 m), and cycle-
20、counter reading in units of 100 clycles. The hydraulic machine had an operating frequency of Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1200 cpm, a load capacity of 100,000 pounds (445 kN), and a cycle-counter reading in units of 100 cycles. As
21、a hydraulic unit, the combination machine had an operating frequency of 50 cpm, a load capacity of 132,000 pounds (587 kN), and a cycle-counter reading in units of 1 cycle. As a subresonant unit this machine had an operating frequency of 820 cpm for the specimens used (a func- tion of the natural fr
22、equency of the system), a load capacity of 110,000 pounds (489 kN), and a counter reading in units of 100 cycles. machines is further described in references 1, 2, and 3, respectively. Each of these testing Loads were monitored continuously by measuring the output of a strain-gage bridge cemented to
23、 a weigh bar in series with the specimen. sion was approximately k1 percent. Heat-deflecting baffles were used for ther- mal protection of the weigh bars on the 20,000-pound (89-k) and the 100,000- pound (445-kN) testing machines. In the combination testing machine, no thermal protection was require
24、d for the weigh bars because of the horizontal arrangement of the bar with respect to the heating furnace. Monitoring preci- Special apparatus was developed to conduct the elevated-temperature tests (fig. 3). Three 1/2-inch-thick (l.27-cm) graphite blocks were placed in contact 7 Carbon Block -Heati
25、ng Slab Pressure Plote Pressure Screw Steel Fromework -Viewing Slot -Specimen Location L-65-9528.1 Figure 3.- Elevated-temperature-test apparatus. with the specimens. Go were placed on the observation side, one above and the other below the region of crack growth. A 1/2-inch (1.27-cm) gap was used t
26、o provide an unobstructed view of the growing crack. The third block was located on the opposite surface of the specimen immediately adjacent to the crack-growth region. Adjacent to each graphite block was a ceramic heating slab and an insulating pressure plate, in that order. A steel framework havi
27、ng an observation cutout was used to hold the components in position during testing. The components were held against the specimen by three machine screws which jammed against the asbes- tos pressure plate. The screws were carefully tightened to insure thermal contact without introducing significant
28、 friction forces. The surfaces of each component were machine ground until 90-percent contact was obtained between the surfaces of adjacent components and between the graphite and the specimens. A chromel-alumel control thermo- couple was spot welded in the pro- jected crack path near the edge of th
29、e specimen. In preliminary tests, the temperature variation across the width of the specimen using an edge control point was found to be less than k5O F (k3O K). 5 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Temperature control was maintained wit
30、hin f2O F (+lo K) in the 550 F (561O K) tests by a controller recorder which regulated current through a satu- rable reactor. The 60-cycle single-phase a-c controller operated on 208 volts. The equipment used to conduct the cryogenic-temperature tests is shown in figure 4. Solid blocks of dry ice we
31、re mounted in the same steel framework used .- Pressure Plate -Pressure Screw Steel Framework -Viewing Slot - L-65-9529 .1 L-63-9530 (a) Steelwork with dry ice installed. (b) Insulating box installed. Figure 4.- Cryogenic-temperature-test apparatus. for the furnace. surface in the same manner as the
32、 heating components. The temperature was con- trolled by the temperature of the dryice and was found to vary less than +2O F (+lo K) across the width of the specimen. The average temperature was found to vary less than +5O F (*3O K) during the course of a test. The sublimation rate of the dry ice wa
33、s satisfactorily controlled by insulating the entire cooling 6 These dry-ice blocks were held directly against the specimen Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-apparatus from circulating air drafts. Frost buildup on the specimen surface w
34、as controlled by periodically spraying the specimen with ethyl alcohol. In all the room-temperature tests and in the elevated- and cryogenic- temperature tests in which compressive loadings were applied, two lubricated guides similar to those described in reference 4 were used to prevent buckling an
35、d out-of-plane vibrations. Light oil was used to lubricate the surfaces of the specimen and of the guides in the room-temperature and cryogenic-temperature tests. In the elevated-temperature tests dry molybdenum disulfide was used for the lubricant. One of the two plates contained a 1/2-inch-wide (1
36、.27-ma) cutout across the width of the plate to allow visual observation of the region of the crack. In the room- and cryogenic-temperature tests, a clear Plexiglas insert was fitted into the cutout to prevent buckling in the observation region. In the elevated-temperature tests, a pyrex insert was
37、used for this purpose. Test Procedure Constant-amplitude axial-load fatigue tests were conducted under positive mean stresses of 40 ksi (276 MN/m*) for the stainless steels and Re 41 was slightly lower at elevated temperature than at room temperature. The crack-propagation curves for AISI 3Ol and AM
38、 350 (20-percent CRT) in of 20 ksi (138 MN/m2) and higher, the figures 5 and 6 indicate that, for cracks grew much faster at elevated temperature than at room temperature. For Sa slightly faster at room temperature than at elevated temperature. No explana- tion for this small reversal in resistance
39、to crack growth can currently be offered. The decreased resistance at elevated temperature at the higher stress levels may be attributed to the deterioration of tensile properties at that temperature. Sa of 10 ksi (68 MN/m2) and 5 ksi (34 MN/m2) cracks in these two materials grew The crack-propagati
40、on curves for AM 350 (DA), PH 15-Mo, FH 14-8M0, and Re + c m - aJ 0.5 1 0 0 L 0 0 - - Sa = 20 ksi ( I38 MN/m21 Sa = 5 ksi (35 MN/m21 - 8OoF ( 300K) 55O0F(56l0K1 -I 80F ( 300K I _ -2.5 2.0 -I .5 .o 0.5 0 81 11 I 101 I 03 I 05 I 07 N. cycles ,I 101 i2e5 Sa = 40 ksi (276 MN/m21 S50F( 56 I OK1 - Sa = IO
41、 ksi (69 MN/m2) 12.5 I I N. cvcles N. cvcles ; IT w C aJ m - Y 0 0 L 0 Figure 5.- Fatigue crack-propagation curves for AIS1 301 (50-percent CR). S, = 40 ksi (276 MN/m2). 9 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I .o C ._ S +. m 5 0.5 - Y 0 0
42、 L 0 0 I .o C ._ C +. m c _“ 0.5 Y 0 0 L 0 0 Sa = 60 ksi (414 MN/m2) sa = 20 ksi (138 MN/m2) I I ,I-,I 81 1 +. IJI - Y 0 0 0.5 2.5 2.0 ; 0 S +. 1.5 W - Y .o 0 L 0 0.5 0 2.5. 2.0 . E 0 .c m C W I .5 - - 1.0 Y 0 L 0 D.5 n 0 I 101 I 03 I 05 I 07 N. cvcles Figure 6.- Fatigue crack-propagation curves for
43、 AM 350 (20-percent CRT). S, = 40 ksi (276 MN/m2). 10 .- . . . -I Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I .o - - 60F(300K) 550F( 56 I OK) c ._ 2.0 ; 1.5 c- + m c D -1.0 - 1 0 0 L -0.5 “ m 6 0.5 - Y 0 0 L 0 C + c m - - 0.5 1 “ L 0 0 0 Sa = 6
44、0 ksl (414 MN/m21 I I I I I I .o C C + C m - 0.5 1 “ L 0 0 L 1 L Sa = 20 ksi ( 138 MN/mz) 1 L S, = 40 ksi (276 MN/m2) ,I I1 I I 1 I 1 I 101 I 03 I 05 I 07 N. cycles -I 2.0 ; q I I I I I I lo I 1 2.5 Sa = 10 ksi (69 MN/m2) 80F( 550aF( II II L N. cycles Sa = 5 ksi (35 MN/m2) I 101 I 03 N. 72.5 - 2.0 0
45、 0.5 I 07 ,I I I 05 cvcles Figure 7.- Fatigue crack-propagation curves for AM 350 (DA). S, = 40 ksi (276 MN/m2). 11 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I .0 C ._ S + m k 0.5 - Y 0 0 L 0 c .c c + m 0 0 L “ Y 0 I .o .- - 0 0.5 Sa = 60 ksi (
46、414 MN/vJ r - Sa = IO ksi (59 MN/m2) -2.5 - 2 .0 - 1.c 0 - 0.5 I ,I ,I ,I ti IO - S, = 20 ksi (138 MN/m2) 80F(3000K1 55OoF ( 56 I OK) - I L_LIl L S5OoF (56 I OK). - - 0 So = 40 ksi (276 MN/m21 -2.5 -2.0 -I .5 I .0 0.5 2.5 2.0 . E 1.5 C 0 - 1.0 Y 0 L 0 1.5 0 0 I ,I ,I ,I ,I 11 N. cycles 0 S * m c 0 -
47、 Y o L 0 Figure 8.- Fatigue crack-propagation curves for PH 15-7Mo (TR 1050). S, = 40 ksi (276 MN/m2). 12 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I .o c ._ C + m c - 0 0.5 1 0 0 L 0 0 I .o C + m c w 0.5 0 1 0 L U 0 1 Sa = 60 ksi I414 MN/m2) -
48、 Sa = 20 ksi 138 MN/) -105F( 195:K) - ttOF(300 Kl 55OOF ( 56 I K 1 101 I 03 I 05 107 , 101 I 03 I 05 I 07 1 2.5 Sa = 40 ksi (276 MN/m2) -109F( 195K) 8OoF( 300K) 550F(56loKl -. 3 C BOF( 300K) - Oe5 * 55O0F(56l0K) 550F ( 56 I OK I -1.0 0 0 L 1 0 0 0.5 ._ r + m I .O r Sa = IO ksi (69 MN/m21 - C ._ + r m 0 0.5 - - 55OoF( 56 IK) C 80F( 300K) - - Y 0 L 0 0 I I I I I I - sa = 5 ksi (35 MN/mz) -2.5 -2.0 ; 0 r w -1.5 al 550F( 80F( 300KI 56 IKI - Y -1.0 g L 0 -0.5 I ,I I 1 I I 0 N. cycles N. cycles E 0 Y 0 0 L u I 101 I 03
