1、RESEARCH MEMORANDUM ADDITIONAL FATIGUE TESTS ON EFFECTS OF DESIGN DETAILS IN 355-T6 SAND-CAST ALUMINUM ALLOY By I. D. Eaton and John A. Youra Aluminum Company of America Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA RM 53L22 RATIONAL ADVISORY
2、CCMMITTEE FOR AERONAUIICS c RxmARcH mMoRANDuM Y . ADDITIGT!MLFATIGUETESTS ONEEFlX!IS OF DESIGNDETAILS IN 3556 SAND-C ALUMINN my By I. D. Eaton and John A. Youra SUMMARY Additional static and fatigue tests were made on aluminmalloy 355T6 sand-cast specimens. Direct-stress fatigue tests were made on p
3、late-type specimens with a single l-inch-disme terlas-cast cored hole and on specimens in which the cored hole was reamed to lz-inch diameter. In addition, direct-stress fatigue tests were made on 0.300-inch-diameter specimens, with various degrees of porosity, machined from the butt ends of plate-
4、type specimens. Comparisons are made with the results of earlier tests, on plate-type specimens with variations in desie details such as bosses and ribs, given in NACA Technical Note 239. Within the range of stresses used, there were no significant differ- ences in the fatigue strengths of sand-cast
5、 specimens with a l-inch- diameter cored hole when tested with the hole in the as-cast condition or with the hole enlarged l/16 of an inch in diameter by reamfng. When the results of tests on the specimens with a l-inch-diameter cored hole are ccxnpared with results, from the previous investigation,
6、 for specimens in which a small cast boss was removed and a l-inch-diameter hole drilled and reamed in the center of the plate-type specimen there is found to be no significant difference in the results except for a slight difference in the static strengths. The direct-stress fatigue test results on
7、 O-300-inch-diameter round polished specimens indicate no correlation between the fatigue strengths developed and visual porosity ratings. IXLRODUCTION In July of 191 the Aluminum Research Laboratories of the Aluminum Company of America reported in reference 1 direct-stress fatigue test results for
8、plate-type specimens in 355-6 sand-cast aluminum alloy with variations in design details including bosses, with and without centrally Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2 NACA RM 5X22 located holes, and longitudinal and transverse ribs.
9、Following the pres- entation of the results from this early investigation, some interest was shown in a comparison of the fatigue strengths of the plate-type specimen with a reamed open hole, as used in the initial investigation, with a new specimen in which the open hole was cored and thus had enti
10、rely as-cast surfaces. In addition, the question arose as to the effects of various degrees of porosity on the fatigue strength of the plate-type specimens of the initial investigation. Reported herein are results of the addi- tional direct-stress fatigue tests on: (1) a plate-type specfmen with cor
11、ed centrally located hole and (2) 0.300-inch-diameter round polished speckens with various degrees of porosity. The objects of this investigation were: (1) to compare the static and direct-stress fatigue strengths of plate-type specimens, of 355-T6 aluminum sand-cast alloy, having a centrally locate
12、d cored hole with the corre- sponding data from reference 1 for similar specimens with other types of design details such as bosses and ribs; (2) to study the effects of the conditions at the rim of an open hole by comparing the strengths of speci- mens with: (a) a cored hole (type IB), (b) a hole i
13、n which the cylindrical surface was machined by reaming (type lB-1) and, (c) a hole in which both the cylindrical surface and a narrow rim on both faces of the specimen were machined (type 1); and (3) to study the effects of porosity on the fatigue strengths of 0.300-inch-diameter specimens taken fr
14、om the grip ends of the plate-type specimens tested. This work was done by the Aluminum Company of America and has been made available to the National Advisory Committee for Aeronautics for publication because of its general interest. MATERIAL AND SPECIMENS The plate-t;ype fatigue specimen with the
15、l-inch-diameter cored hole, one of the new specimen types used in this investigation, is shown in figure 1. The second new type was obtained by reaming the cored hole to a diameter of 1A inches. 16 These specimens were cast at Alcoas Cleveland Works using the basic pattern previously described in re
16、ference 1. The mechanical properties of the 355-T6 aluminum-alloy sand-cast material as determined at Cleveland on separately cast test bars are shown in table I along with the mechanical properties of the material used in preparing the specimens for the earlier tests. The mechanical properties are
17、found to be in good agreement with the average properties for the several lots of material used in the previous investigation. These properties are found to exceed the specffied values and are in good agreement with typical values given in reference 2 and are in general agreement with Federal Specif
18、ications QQ-A-6Ol-a. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA RM 53L22 3 As was the case for the specimens in the previous investigation, these specimens were radiographed at the Cleveland Works and only those found to be generally sound
19、were submitted for test. Figure 2 shows the three conditions at the edge of an open hole studied, namely, (1) plain cored hole (type X3), (2) reamed hole In plate with as-cast surfaces (type m-l), and (3) reamed hole, machined surfaces (type 1, boss machined flush with plate previous to reaming hole
20、). The 0.3OC-inch-diameter round polished direct-stress fatigue speci- mens Fllustrated in figure 3 were machined from the butt ends of the plsrte-type specimens. Twenty-four spectiens were obtained framthe butt ends of a specfmen which had not been previously tested because of mis- registry of the
21、design detail. The location of these specimens is shown in figure 4. Four additional specimens were obtained from each end of several plate-type specimens which had SCXIE fatigue test history. In each case, the plate-type specimen had tithstood a considerable number of cycles at a low stress (based
22、on the minimum area of the test section) tithout failure. As can be seen in figure 5, which illustrates the loca- tion of the small specimens WI-thin the butt ends, spews A and B were taken from a section of the butt end beyond the keyway through which the load was transferred and thus should not ha
23、ve been subjected to any significant stress cycles during the fatigue testing of the plate-type specimen. Even though the small specimens C and D were taken from por- tions of the butt end which had been subjected to a cyclic stress, it is believed that the stresses were so smaU that the behavior of
24、 these speci- mens would show no effect of the previous stress history. As wUl be seen later, the results for specimens taken from these two locations (speci- mens C and D) gave fatigue test results which were consistent with the results of specimens taken from nonstressed material (specimens A and
25、B). PROCEDURE One static and five fatigue tests were made on specimens of the type shown in figure lwith a l-inch-diameter cored hole (type IB). In addi- tion, three fatigue tests were made on specimens in which the cored hole had been reamed to l that is, the fatigue strength reduction factors are
26、lower for the 355-T6 sand castings than for the rolled bar. The results of static and fatigue tests on 0.300-inch-diameter round polished specimens machined from butt ends of plate-type specimens are given in table V. Included in the table are the porosity ratings based on visual observation of the
27、machined surfaces of the specimens. The results of fatigue tests at zero stress ratio are plotted in fig- ure 8. In this figure, the results have been separated according to the porosity rating of the individual specimens and a band of results is shown which encloses all the test results. Study of t
28、hese test results shows that no one of the following criteria gives consistently high or low results in the band of results shown: (1) porosity rating, (2) indi- vidual plate-type specimens from which the round specimens were obtained, (3) location of specJmen within the butt end, or (4) direction o
29、f the axis of the round specimen with respect to the longitudinal axis of the plate-type specimen. It can be seen in figure 8 that there fs no correlation between the porosity ratings and fatigue strengths of the specimens. For any of the porosity ratings for which a reasonable number of specimens w
30、ere tested itcan be seen that the results cover the major portion, if not all, of the band of results shown. Further, specimens having the greatest degree of porosity helped to define the upper limit of the band of results and other specimens having a slight porosity rating, which is classed as next
31、 to the least porosity, helped to define both the lower and upper limits of the band. In figure 8, the specimens obtained from the butt ends of the plate- type specimen which had no previous stress history are indicated by solid symbols. It can be seen that the results of these specimens extend from
32、 the lower l fartypes 2to 6 imluaive, eectionteknet. edge of boss tx rib. b trees comratiotl faztor aquxla ratio of temile St- cf sepmtely cast test bare to that; cu plate-type 6pec*n. %aLutim 6pedml type; all other6 repm-teu ia ref. 1. -I- I I . . . 1 Provided by IHSNot for ResaleNo reproduction or
33、 networking permitted without license from IHS-,-,-I , . TABLE III RCATIC ANI PATIm TEEE l3WJDTS OF 355-T6 AIimmud-ALLOYW-CAsrPIATE SPECPIENS ElmziG AN -RCED HOLE AT (I!EWER OF TEST !3IX!l!ION NOlIlhil iic+xd. 1 Namhal stress,b P/A, 3pecim3-i conaitlon, lb msxirmrm Psi cycles to lo 57,500 57,500 0 3
34、2,460 static D-l A-l -55 ;,5g m,53$ 0 0 1”9 464 14,400 Through central boll A-2 170 removed A-3 la D-4 li -1 - - - - - IIF STATIC TESTS NUMBER OF CYCLES TO RUJFIE 1 1 c oi 108 9 F Figure 7.- Direct-stress fatigue test results on 355“T6 alumina alloy sand-cast SpeCFraens. Plate specimens with single
35、open hole. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I , , , IO 10“ lo“ Figure 8.- Direct-stress fatigue teat results for 355T6 sad-cast aluminum aaY. ERecta of variation in prosi-. Btress ratio LI E = 0. Provided by IHSNot for ResaleNo reprodu
36、ction or networking permitted without license from IHS-,-,-03 MAMETW TES SPEWEN FOR OETALS SEE FIG 3) / I I I 1111 i I BAND OF AXIAL FATIGUE TEST RBUTS F22 L-92099 .gure l.l.- Typical fatigue fracture of sand-cast specimen with unreinforced open hole. (As-cast hole shown.) NACA-Langley - a-10-64 - se0 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
