Fatigue Crack Paths 2003

Aamea,,(DOB = 0, Adm< 0)}, A a m m ( D O=B-1/2, Adm2 0) = min{Ao'mean(DOB = -1/2

,A6,,, 2 0), Aamea,,(DOB = 1/2, Adm < 0)}, Aamea,,(DOB = 1/2, Adm 2 0) =

min{Aamea,,(DOB = 1/2, Adm2 0), Aamea,,(DOB = -1/2, Adm< 0)}, Aamea,,(DOB = -1/2,

Adm< 0) = Aamea,,(DOB = 1/2, Adm2 0) and A a m m ( D O=B1/2, A G m <0) = Aamea,,(DOB

= -1/2, Adm2 0). This definition means that the compressive load cycle is as damaging

as the tensile load cycle if in both cases the corresponding nominal stress distributions

of stress ranges are the same but opposite. O n this waypredicted meanfatigue strengths,

210mm,in “as welded”condition are presented as 3 Dgraphs in Fig. 2, w h e nT/t = 1 and t

= 25 m m .

O n the basis of all predicted mean fatigue strengths in “as welded condition”, the

theoretical fatigue classes were calculated, Eq. 3, and curve fitted using non-linear

regression analysis with 3rd degree polynomial, Eq. 6.

FATDOB =

f0)

(6)

The theoretical thickness effect correction factor, f(t), is also included in Eq. 6. It is

conservatively assumed, that f(t)=L2L5] 6 , when t 2 25 m mand f(t)=1, when t <

25 m m . The coefficients ADOBJ- corresponding to the certain D O Band exponents a,-, b,

and c,- are presented in Table 2, whenAdm2 0. If Aom< 0, then Am,- = A_1/2,,- and A_1/2,,- =

A101, wherethe in both equation the later terms are the coefficients for A d m2 0.

D O B= i n )

D O B= -0.5, A0,.“ 20 or D O B= 0.5, A0,, < 0

Figure 2. Predicted m e a nfatigue strength, Acme,” (N= 2><106 cycles), in “as

welded”condition, T/t = 1 and t = 25 m m .