1、1II,III1III1i-NATIONAL ADVISORY COMMITTEEFOR AERONAUTICSTECHNICAL NOTENo. 1705EXPERIMENTAL INVESTIGATION OF THE EFFECTS OF PLASTIC FLOWIN A TENSION PANEL WITH A CIRCULAR HOLEBy George E. GriffithLangley Aeronautical LaboratoryLangley Field,Va.=3!WashingtonSeptember 1948. ,-./,(,?,(; I. . Provided b
2、y IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-TECH LIBRARY K.AFB. Nhl.NATIONAL ADVTSORY CmMmCmmIllllllllinlllnl!iulllClJ949bbFm KERommcs!mcmncAL nom no. 1705RVVE3TIGATIOI? OF TEE EFFECTS 0F3?LASTICFLOWR!JATE3!J310HX!MTE L-AC lRCUIAR HOLE ,By George X. Griffi
3、thSeven uniformly Mmepsioned 24S4 tension yane with a central .circuler hole were subjected to various loads in order to study theeffects of plastic flow at the petit of maxhiim stress concentration.The results, Pesented in graphical fq show that, as the amount ofplastic flow increases, the stress c
4、oncentrationfactor is ayprecialilyreduced and the strsdn concentration factor is appreciably increased.Subjecting the panels to 100 repeated loading cycles caused no changea71 to occur t?lths memmlm values of the streflsand strain concentrationfactors.b structuralmenbers= d.iscontinuitiessuch as hol
5、es producestress concentrateions but -theeffects of plastic fluw on such stressconcentrations,esp3ciaUy under releated loads, are not generaldylmown. Because tb localizing of high stresses is %elieved to he theforermmer of failure under reyeated loads (fatiguefaihme), stressconcentrationsme consider
6、ed to %e more serious fi fatigue than instatics.The purpose of the Wesent investigationis to deterndne, for asimple case of stress concentration in a tension panel with a central.hole, the effect of plastic flow in mdi in theplastic range, stress characteristics in general are then quite clifferentf
7、rom strdn characteristics. The discussion is therefore divided intotwo pas, one for elastic behavior, the other for hdastic behavior.In the ffist yert, which is concernedwith elastic action, no distinctionis necessery %etween stmesses and strains; hence it will be unnecessaryto mention slnxdm. h tha
8、t part of the discussion dealing tith plasticaction it is perhapsfor the stmins wereconvertedfrom theseme logical to discuss the strain results ffist,actually measured, whereas the stresses must 30Straim .-ic BehaviwStress concentrationfactor.- The theoretical madmum value of thestress concentration
9、at the edge of a cticular hole in a straiglrttensionmember of inite width is three times the applied uniform stiess(reference1). Coker and Ffion (reference1) regard this velue asapproximately correctwhenever the plste tidth is four or more Wines thehole dismeter, and Timoshenko (reference5) concursw
10、ith this optrdonif the tidth is five or more times the dianeter. Shoe + ratio of yl.atewidth to hole diemeterwas six for the test panels, a theoreticalstress concentrationfactor of 3.00 can be accepted. The value obtainedexperhentaJJy (average of 5 tests durhg the first cycle of loading inthe elasti
11、c range) was 3.08 (2.7 percent higher than the theoreticalvalue). terms of net-section stress, which provides perhaps a moredesirable comparison in dealing with static stress analysis,when theplate width is six ttmes the hole diameter, the theoretical stressconcentrationfactor %ecomes 2.50. The corr
12、esponding eqerhentalvalue (5 tests) was 2.57. Available photoelastic resuLts (referencealso give s that is,the mexinum load in test 6 was greater than in test 5 and consequentlythe strati of test 6 traced the strains of test 5 and extended tohigher strains. The top surface of the fime was then obtai
13、ned bydrawing smoth curves through these test potits. The test results werevery consistent,very little scatter occurring in the test points. : - -y - -,Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA 0. 1705 . 7Fie 7waE obtained by connecting th
14、e strains (or te:t oints)measured whn the load, during the first loading cycle, returned to zero.Figure 7, therefore, reyesents the net amount of stretching or elongationremaining when the panel load has leen released. The over+ll changein strain, as the load varied from a madnumto zerb, would be oM
15、ainin the other tests it is probably quite small.Two sources of error are present in figure 3. The ffist is a slightclifference between the measured strdn for any particular tes%and the strain correspondingto the same maximum lod on the straightMns through the test points as the yanel unloadd. The s
16、eineeffect tothe same degree was experiences in the aary tests hut is not shownin figure 4. This effect is %el.ieve Jarge strains change the originalgage length and the true unit strain is thereby affected. ,.The ranges of sss and strain dqend upon the factors discussedin the foregoing paragraphs. T
17、hese ranges me shown in figure 10. Theactual stress and strain range curves were based on tti experntalresults which led to figures 3 and k in the manner .“, .Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA NO. 1705 uTABLEl.- PA?iEhDIMkKSONS/She
18、etthickness(in.)Gross+ection l?et-sectionsreti exea(Sq in.) (Sq in.)Holediameter(in.)Width(M.)Panel120.0895.0898.0891.08a6.02.08g2.08a23.9983.9984,0003.9993.9983.9983*9992.1442.159!2.1432.1262.1402.1412.u71.7861.8001.78623.9524.o424.0524.oO23.9924.0024.00l*fi21.78456 1+3.41.7647I.: TA131J32.- TEsT S
19、CHEDUIJIAveragen891:0/45.555.065.023.525.530.736.040.845.950.610010010010010010010011111110056 567 7 25.330.636.18 2g.;91:063.741.736.0Z*336.049-, - - _ - _. .Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-12 ACA NO. 170550 1 Theoretical (reference
20、I)40o Electromagnetic gageExperimentalO SR-4 type A-5 gage30 -Stress, o, ksi20 -u- .u u100 I II I I0 2. 4 6 8 10Distance from edge of hole, in.Figure l.- Net-section tensile stress distribution typical of results obtained inelastic range. P= 30 kips; OOv=16.4 ksi.2.52.0Stress 1.5concentrationfactor
21、1.0/0.5Transverse I TIo II 10 2 4 6 8 10Distance from edge of hole, in.figure 2.-Theoretical stress concentration factors (based on average net-section stress) for tensile stress and transverse tensile stressacross the net section. (Reference 1-).- . . -.- - -,- Provided by IHSNot for ResaleNo repro
22、duction or networking permitted without license from IHS-,-,-.13.100.80,.60Panel Iood, kips40200,/ ;oQ 07I I I Io 5 10 D 15 20 25V 30 35 4oxIcj3Stroin, Figure 3.- Stroins measured by the /II/ II/.w,ksi45 “/ /o/. 501 ,02 4 6 8 m ,.-CXstancefrornedge). -. .Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
