1、METAL STRENGTH CHARACTERISTICS AT TWO STAGES OF FATIGUE FAILURE AND DIFFERENT TEST BASES M.Ya.Galperin UDC 539.431.043.3 It has been shown in 1-5 that when the fatigue failure process is divided into two stages it is possible to make a more complete characterization of the strength properties of met
2、als used for making machine com-ponents and supporting elements of structures.The random overloadings occurring in metallic components in operation due to variable loads often lead-in the presence of fatigue macrocracks(even of relatively small size)-to serious fractures and break-downs.Therefore it
3、 is necessary in strength calculations to determine the durabilities and strength limits of the metals used not only at the final stage of failure but also at the stage of fatigue macrocracK formation.In order to clarify the difference in the fatigue characteristics of structural metals relative to
4、cycles and failure stresses when the fatigue failure process is divided into two stages the results of large-scale bend-ing tests of rectangular section testpieces of types 45 and St.3kp steels and type AV aluminum alloy have been used together with data from 6 for round-section testpieces of high-s
5、trength nodular graphite cast iron.The mechanical properties of these materials are shown in Table 1.In order to study the fatigue failure relations on full-sized testpieces of noncircular cross section,the tests were carried out using rectangular sectioned beams of width b 24 mm and height h=90 mm.
6、The dis-tance L between the supports was 700 mm(Fig.la).In the selection of the metal for this part of the investiga-tion static tests were made in axial tension of the testpieces of type 45 steel from five different melts,dH=10 mm,/working=5dH)cut along the rolling direction from plates of cross se
7、ction 25 100 mm.The results obtained showed that as the hardness of the metal changed there was a marked change of the strength and plastic properties(Fig.2).800 C-&L;IJ J50-I e f Fig.1.Sketches of testpieces.Translated from Problemy Prochnosti,No.5,pp.22-35,May,1978.Original article submitted Octob
8、er 18,1976.518 0039-2316/78/1005-0518507.50?9 1979 Plenum Publishing Corporation TABLE 1.Mechanical Properties of the Materials Investigated*Testpiece material Type 45steel(strip,25x 100 ram),melt 142 Type 45 steel(strip,25 100 mm),melt 145 Type 45 steel(sheet,=11.7 ram),melt 369 TypeSt.3kp steel(st
9、rip,4 30 ram)melt 6534 Type AV luminum alloy(testpiece cut from com-ponent)High-strength nodular graphite cast iron(bars of diam.85-90 mm and length 400 ram)Condition of materml kgfnam kgf/mm As supplied The same Formed profile Cast in sand molds 35,5 39,3 39,4 29,4 31,5$52,0$66,0 74,5 73,3 43,9 34,
10、5 83,0,%23,0 19,0 15,5 33,0 I 14,0 2,3,%|3,1 9,18,:12,t7r Strength limit ofsmh test-t I piece(No-/10 dH=7.52 2,9 187 30,0 5,5 217 31,4 4,8 217 33,5 9,4 121-,95 13.2 1,32 0,43 277 27,0*Each value was determined as the mean from five or more testpieces.?9*Testpiece cut out transverse to roiling direct
11、ion.r ield point.*Pure bending with rotation.45 J5 i/,0 b,kgf I mm z I w,.4r-&O5 35 20 30 5 185 I95 275 215 HB,kgf/mm 2 Fig.2.Mechanical properties of type 45 steel strip(section 25 x 100 mm)of five different melts as a function of surface hardness HB.The beams(testpieces)for fatigue testing were pr
12、epared from metal plates of the two melts 142 and 145(see Table 1)which from the static test results(see Fig.2)differed the most in the hardness value(I-IB=187 and HB=217 kgf/mm2).The middle parts of the working sections of the beams were ground.Beam testing with repeated bending in the plane of gre
13、atest rigidity was carried out on a model ZDM-Pu-100t hydraulic pulsing machine with an asymmetry coefficient min/ma x=0.11 and a loading frequency of 300 cycles/min.Testpieces with unmachined(black)surface were made from plate(5=11.7 mm)of type 45 steel 519 TABLE 2.Mean Values,Standard Deviations,a
14、nd Coefficients of Variation of the Fail-ure Stresses(or strength limits)for Testpieces of the Materials Investigated at Various Test Bases(s.I.=strength limit)Characteristics determined(1.kgf/mm2 S(%)s.1.kgf/mmZ v(8.)L,%(%)s.1.kgf/mmZ S(a)s.l.,kgf/mm 2 v(%)s.L,%;_,kgf/mm2 S f kgf/mm 2 V_ 1,%kg f/mm
15、z S._ 1,kgf/mm z VE_t,%kg f/mmz S 2?9.-1 kgf/mm V_l,%(s.1.,kg f/mm Sal s.1.kg f/mm V60 s.L%a-t,kg f/mmz S_l,kgf/mm z V_,%_pkgf/mm z SE_,kgf/mm s VF_g%Test bass Nb,cycles,o.I 4.,o.I,o,I,.,o I,o,o,o.m B w B 44.0 1,9 4,3 22,5 25,2 0,75 0,8 3,3 3,2 AIuminum alloy AV 14,1 10,8 _ 16,7 1,7 1,0 _ 1,4 12,1 9
16、,3 _ 8,4 w m Type 45 steel,melt 142 24,3 23,0 24,8 23,3 0,26 0,30 0,34 0,38 1,I 1,3 1,4 1,6 b-24 ram;21,4 21,6 0,40 0,43 t,9 2,0 h=90mm;r=120;aa-l,0)20,8 20,0 21,0 20,2 0,43 0,38 0,44 0,44 2.1 1,9 2,1 2,2 D D Type 45 steel,melt 145(5=24 ram;h=90ram;r=120 ram;%1,0)26,9 23.0 22.i 21,0 28.2 23,2 22,3 21.3 0.71 0,54 0,50 0.42 0,86 0,48 0,45 0,43 2,6 2,3 2,3 2,0 3,0 2,1 2,0 2,0 Type 45 steel,melt 369 h=5=l 1,7mm;r=62,5mm aal,0)43,2 34,9 28,0 25,8 22,7 47,4 38,3 30,I 27,1 23,7 3,3 3,7 3,3 3,0 2,7 1,9
