ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN ANN ARBOR. MICH. FIFTH PROGRESS REPORT TO MATERIALS LABORATORY WRIGHT AIR DEVELOPMENT CENTER ON EFFECT OF PRIOR CREEP ON MECHANICAL PROPERTIES OF AIRCRAFT STRUCTURAL METALS by J, V. Gluck H, Ro Voorhees J. W, Freeman Pr:ject 2498 Air Force Contract Nco, AF33'61.6)-3368 Task No. 73605 Februa.rv 9,.1957

SUMMAR Y This report covers progress under Contract AF33(616)13368 for the period from October 21, 1956 to February 9, 1957 on a study of the effects of prior creep on the short-time mechanical properties of three aircraft structural metals. The materials under study include: 2024-T86 aluminum alloy; Cl110M titanium alloy; and 17-7PH precipitation hardening stainless steel., During the period covered by this report a draft report summarizing the work accomplished during the first year of the contract was written for submission to the Wright Air Development Center. In addition, a brief paper outlining the scope of the investigation and including some preliminary results was presented at the Florida Conference on High-Speed Aerodynamics and Structures held at Gainsville, Florida, January 22 - 24, 1957. Work accomplished during this period after the completion of the summary report included the establishment of a sampling procedure for the C110M titarniurnm alloy, preliminary tensile tests of C-110M at room temperature and initial creep tests at 700' and 800'F for this material, The Investigation of the 17-7PH(TH 1050 condition) was continued to c(over the effects of variable amounts of total deformation in 100 hours at 800' or 9C00F on the subsequent room temperature tensile properties, The data indicate that.n.r:eased amounts of total deformation up to 2, 25 percent result in increased strengths,, However, the principal strengthening effect comes from the exposu:re to temperature alone,

INTRODUCTION This report, the fifth progress report issued under Air Force Contract No, AF33(616)-3368, covers the period from October 21, 1956 to February 9, 1957, The purpose of the investigation is to study the effects of elevated temperature prior-creep exposure on the mechanical properties of three aircraft structural sheet alloys The materials and temperature ranged under investigation incllude: 1. Aluminum alloy 2024-T86 at 350, 400', and 500'F 2, Titanium alloy C-110M at 6500, 700', and 800'F 3, Stainless steel 17 7PH(TH 1050 condition) at 600', 800' and 900F Both stressed and d unstressed exposures are to be carried out for times,f 10, 50, cr 100 hours. The stressed exposures are to be carried out to 0, 5,.1 0, 2, 0, and 3, 0 percent total deformation where practicable, The total deformation is defif.ned as all deformatiomn, elastic and plastic, occurring during the application of the load and during the creep of the specimen at the testing stress and temperature, Fol.lowing these specified exposures, the materials are to be evaluated with respect to the following properties at both room temperature and the temperature of prir creep exposuire shortdtime tensile properties; short-time compression. properties; tens iNon-impact strength; and hardness at room temperature, Metal.lur gical studies will be carried out where significant effects are noted to explain their c as. aS e. The test stresses for the nominal exposure conditions a:re determ.:ined ~rom cu.rves of stress versus time for a given total deformation, established for each material at each testing temperature, Replicate exposure tests were run for many of the conditions in order to ensure generality of the results, The basis for compariscon is to be the normal properties of the unexposed material established through 9 or 10 tests.of samples chosen randomly from the various sheets of material,,

2 The test materials were procured as approximately 0, 064- ipch thick sheets, The test direction for the aluminum and stainless steel was specified to be the direction crosswise to the sheet rolling direction, while the titanium alloy is to be tested parallel to the rolling direction. The choice of testing direction was determined by a desire to test each material in its weaker direction, The alumir~*m alloy 2024-T86 was furnished by the manufacturer in the cold worked and artifically aged condition, while the titanium alloy C-110M was furnished as hot rolled and annealed. The stainless steel 17=7PH was treated to the TH1050 condition at the University, This treatment consists of aging first at 1400' and then at 1050~TF In the initial contract the principal test effort was assigned to the evaluation of the aluminum alloy, Test Material, Specimen Preparation, Test Equipment and Procedures Inasmuch as the test materials, specimen preparation, equipment, and proocedures have been previously discussed in progress reports as they have been developed, this material will not be repeated here, A complete discussion of these topics has been included in the First Summary Report to be issued shortly, One new topic, that of the sampling procedure for the C-110M titanium alloy, wiil be discussed since it is outside the scope of the First Summary Reports Sanmpling Procedure for C-11OM The sampling procedure for the C -110M titanium alloy was designed to permit the most economical utilization of the material consistent with the specification that it be tested parallel to the sheet rolling direction, Three sheets were arbitrarily selected to be tested. The sheets chosen were all 90 inches long; two were 3 iinches wide, and the third was 34 inches wide, The general sampling scheme for an individual sheet is shown in Figure l,

3 Each sheet was divided into one-inch wide strips running the length of the sheet. For the initial tests of the unexposed properties, strips, 1, 5, 9, etc, as indicated in Figure 1, were subdivided to provide a repeating sampling pattern over both the width and length of the sheet. The remainder of the strips were reserved for blanks for the specimens to be subjected to exposure prior to testing, Over the 90inch length of the sheet, four sections or quarters of length were laid out, One end was designated the "A" end and its subsections labeled AA and AB, while the other end was designated the "C" end and its subsections labeled CC and CD, An individual specimen is identified by a number sequence designating the sheet number, section number, and strip number, RESULTS AND DISCUSSION Tensile Tests of C-110M Titanium Alloy Tensile tests at room temperature were completed on nine specimens of the Cl110M titanium alloy. Three specimens each were tested from the three sheets arbitrara.y selected for exposure tests on this material. The results of these tests are summarized in Table 1. Also included in this table are the manufacturer's repo(rted properties for this heat, The data indicate that the properties of the material are fairly consistent from sheet to sheet, The scatter in properties within individual sheets is about the same as the over-all scatter, with the exception that the yield strength values fo_ sheet 1 are a trifle lower than the values from sheets 2 and 3, Also included in Table 1 are the manufacturer's reported properties for this heat and the typical properties for this material as given in the Rem~Cru Data Sheet on C-110M dated November 1, 1955,.

4 The manufacturer's reported properties for this heat show a slightly higher strength and lower ductility than those determined at the University of Michigan, In addition, the spread between the tensile and yield strength was slightly less than found in the tests at the University. Both sets of actual test results for this particular heat of material appear to well exceed the typical values reported in the Product Data Sheet on C-llOM, This i.ncreased strength was accompanied by no essential sci ri'ice of ductility, Creep Tests of C110M Titanium Alloy Creep tests have been initiated on samples of the C11 0M titanium alloy in order to determine the stresses necessary for the attainment of the desired total deformations in the time periods at the temperatures specified for stressed expc suo;re tests, The temperatures of testing include 650*, 700', and 800'F and total deformations from 0, 5 to 3 percent are to be covered for 10, 50, or 100 hour%, Two tests have been completed to date at 800' and one test at 700'Fo The data are summarized in Table 2, The stresses used so far appear to be within the range desired for the stressed exposure tests. The 10,000 psi test at 800*F showed a continually decreasing creep rate with time over the entire time of testi.ngsomre 300 hours, The 25,000 psi test at 800'F reached a steady creep rate at abl i.t 70 h cu. rs, St;ressed Exposure Tests of 17~7PH Prev.di(cus reports have contained the results of tests of the effects of st:essed expos ore to 2 percent total deformation in 100 hours at temperaturesbetween 600' and 900eF on the subsequent room temperature tensile properties of 17 7PH(TH1Q050 C(,ondition),, The tests indicated that such exposuresresulted in increased tensile and yield strength, with the maximum effect occurring at about 800"850QF. Some test results are now available covering exposure for 100 hou-rs at 800' or 9001F to a range of deformations prior to room temperature tensWlle tests, These data are summarized in Table 3 and plotted in Figure 2,

5 The indicated effects are: 1, Exposure to temperature alone (I zero deformation ordinate of Figure 2) increased tensile and yield strengths and reduced elongation. 2, A prior deformation of 0, 5 percent apparently reduced the increase in strength arising from unstressed exposure. 3, The tensile and yield strengths were of the same order of magnitude and possibly increased with increasing prior deformation for deformations larger than 0. 5 percent. It is difficult, however, to be sure of the trends and magnitude of the effects due to the erratic changes with increasing deformation indicated by the data, 4, Additional exposures of specimens with subsequent tests at room temperature seem necessary to check both the trends and the maximum and minimum as indicated by the apparently erratic properties obtained to date, 5, The data obtained to date indicate no consistent difference in tensile and yield strengths for stressed exposure at 800' and 900F., Elongations, however, were consistently higher following exposure at 900~F.

TABLE 1 Tensile Test Data at Room Temperature for C11OM Titanium Alloy 0.2% offset Ult, Tensile Yield Strength Elongation Reduction of 6 Spec. No. (psi) (psi) (%//2 in. ) Area (%) E x 10 psi/in, 1A=9T 145,000 140,000 22,0 35 2 16,8 1AB-17T 144, 000 1399000 24.0 32 4 16 0 1C-13T 152,000 144,000 21.5 30,2 16,8 Average 147, 000 141,000 23.5 32,6 16,5 2A-28T 146,000 142,000 20.5 32.0 16 9 2C-5T 146,000 144,000 22,3 29.6 16,8 2C-20T 147,000 143,000 21.7 31.6 16, 4 Average 146,333 143,000 21,5 31.1 16,7 3A-13T 147,000 145,000 21,5 30,8 16 4 3A-34T 151,000 147,000 22.5 33.3 16 6 3C-20T 146,000 142,000 22.7 26.4 15,8 Average 148,000 144,667 22,2 30.1 16.3 Average- 9 146,211 142,889 22.4 31.3 16 5 tests Manufacturers 149,400 147,200 15.0 - reported properties for this heat * Manufacturers 130,000 120,000 15,0 32.0 typical properties for this alloy** * Heat No. A1172600 ** Rem Cru Data Sheet, November 1, 1955

TABLE 2 Creep Test Data for C110M Titanium Alloy Time to Reach Indicated Test Tempo Spec. No. Stress Load. Def. Total Deformation (:_F).. ____ (psi) (%) o. 0.5% 1,0% 2,0% 30 Q% 700 1C-5T 50,000.36 28 107, 5 220 a 800 1A-24T 25,000.182 4 11 27, 5 46. 5 2C-1T 10,000.009 52.5 295, 5 a a ~ test discontinued before reaching the deformation,

TABLE 3 Effect of Prior Creep-Exposure on Tensile Properties of 17-7PH (TH 1050 Conditions) Subsequent Room Temperature Tensile Properties Nominal Exposure Conditions Actual Exposure Conditions Ult. Tensile 0.2% offset Modulus lemp lme Iortal Lef. l —me --- tress Total e Strength Yield Strength Elongation Reduction of (*F) (hr) (%) Spec. No. (hr) (psi) (%) (psi) (psi) (% /2 inches) Area (%) E x 10 psi/in. /in. 800 100 0,. 5 3P-T5 100.0 59,000 0.48 208,000 204,000 3.8 17.6 30.3 100 1.0 3H-T5 100.0 70,000 0.89 220,000 215,000 3.5 14.0 32. 1 100 2.0 2S-T6 102.1 81,000 1.88 227,000 222,000 4.2 15.8 30.2 100 2.0 3P-T1 102.6 81,000 2.12 232,000 229,000 3.5 12.1 29.9 100 3.0 3L-T2 100.0 85,000 2.45 218,000 214,000 2.2 20.2 30. 1 900 100 0.5 3G-T5 100.0 37,000 0.47 204,000 196,000 4.5 17.6 29.2 100 1.0 3A-T4 100.0 46,000 0.95 228,000 220,000 4.5 14.4 30. 1 100 2.0 2R-T1 100.0 49,000 1.55 214,000 209,000 6.5 16.7 29.9 100 2.0 3G-T2 100.0 50,000 2.04 224,000 219,000 4.0 15.2 29.7 100 2.0 1Q-T22 100.1 50,000 2.33 235,000 230,000 4.0 13.1 30.0 100 3.0 3Q-T4 100.0 52,000 2.30 221,000 219,000 5.0 14.9 31.0

Section CD Section CC Section AB Section AA Strip CD1 I ___ DI __C1T I __ AB1 \ AlT No. 09 r C2 A2 E v-^ ____________________C3 A3 5 I C5M2ICCIc C$T A4l AA5M2IAkC AAT JC gA t';rg __________________C6 A6 ^~.~~~~~~~~~~~0 __________________C___________________________________________A7 o, 5 j~~~~~~~~0 ___________________C______________________________A_ C 6A C8 09 P,=r~ C^v 09 C9T |c9M1 |C9C A9 I A9T | A9M| LO ^ _________________________________C10 ____ x ^___________________________________________AH Cd O ^_____________C12 A12 0 ^ 3C I C13T C13M C13 134 I _ A13T I A13 I S ___________________________________________ A1U _______________________ _______________________A 1g 5 ________C16 _______________16 o - CD17T I CC17 AB17T AAl mt c~~~~~~~~~~~~18 l cE PI p______________C19 iA19 CD20 CCT AB20 AA20T C?) A21 O> 0______________C22A22 C23 A23 5 C2[4 c InCc2 C24 I 2T I A24 I A 2LM A24T "S ~~~ ______________________C25 A25 H 0_________________C26 A26 Pg~~~~~~~~~~ _____________ 0C27 A27 L h28d C28MI C28T C28 LBd AL28MI A28T I A2 c3 n__________________ C29 A29 C A30 0b *fI C~__________ C31 A31 ~ g ________________C35A a~ rt- ~ CD36T C36 AB36T AA36 0

TENSILE AND YIELD STRENGTH 240 900'F 230 * ~\ \/ / ~ Tensile Yield.o / St e Strength S gJ~ \A/ a Unexposed 200 \ / -l —-- 800F-100 hours d Unexposed ELONGATION 0 800F-100 hours 5 # * 900-F-100 hours 0 0 0.5 1.0 1.5 2.0 2.5 Prior Total Deformation - percent Figure 2. - Tensile Properties of 17-7PH(TH 1050) at Room Temperature After 100 Hours Prior Creep at 800' or 900F. 0 0, 5 i, 0 i, 5 2, \ k,A'~~~fe \0 / or Stir reng th St~ rengthF