Creep-fatigue life prediction in terms of nucleation and growth of fatigue crack and creep cavities
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0 0 45 90 Fig. 13--Comparison of CMTP predictions (/72 yield function) and experimental data (e) for various metals displaying the texture components indicated. (--4--) Taylorassumption;( t3 ) KochendSrfermodel. (a) Copper with a strong {100}(001) texture/3 (b) Iron single crystal sheet: {100}(011) orientation.19 (c) Cold rolled and annealed low C steel: {100}(012) orientation.35 (d) Iron single crystal sheet: {l12}(1T0) orientation.'9 (e) Cold rolled and annealedlow C steel: {411}(14g) orientation.35
with experimentally determined R(O) curves. These are displayed in Figure 16, where the work of Ito et al. 27 is displayed, and in Figure 17, where the results of Parni~re 19are shown. It is evident from Figure 16(c) that the sharp R-value variation is accurately predicted. However, in the case of the other steels, the CMTP predictions underestimate the amplitudes of the R(O) curves, although the positions of the R extrema are well reproduced. The relative inability of the present yield functions to reproduce the full extent of the R-variations can be readily explained by their smooth nature I 1 4 - - VOLUME 19A, JANUARY 1988
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Fig. 1 4 - - R ( 0 ) curves for the f o l l o w i n g rolled sheets: (a) C u - R , (b) 5 pet Z n - R , (c) C u - 2 0 pet Z n - R , (d) Cu-P, (e) Cu-5 pet Zn-P, ( f ) 20 pet Zn-P, (g) Cu-F, (h) Cu-5 pet Zn-F, and (i) C u - 2 0 pet Z n - E E x p e r i m e n t a l R - v a l u e s taken f r o m Ref. 18. ( o o ) Fj (n = m = 1.5) a n d ( tJ [] ) F2 criteria used with the K o c h e n d 6 r f e r model. texture d a t a used are those reported in Ref. 18.
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(see Figures 7 through 10), which leads to reduced fluctuations in strain rate through the normality rule. By contrast, in crystallographic calculations,12 the R-value variations are frequently too pronounced. The results published by Stephens, 2~ Kallend and Davies, 28'29and Svensson 3~ on yield stress measurements pertaining to cold rolled and annealed sheet are shown in Figures 18 through 20, respectively. The CMTP calculatio
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