Crack Paths 2009

critical cross

section

a)

b)

(2)

(1)

(3)

Figure 5. Fatigue testing machine (a) and testingbar (b)

Computational Analysis

A stress and deformation field in the critical cross section of the bar has been

determined numerically using FEM-programcode Abaqus [7]. The FE-model shown in

Fig. 6a and loading pattern shown in Fig. 6c have been used in computational analysis.

In the next steep, the fatigue analysis has been performed using FE-Safe program code

[8]. The fatigue analysis is based on strain-life method (-N), where Coffin-Manson

relationship with Morrow mean stress correction is used to determine the number of

stress cycles Ni required for the fatigue crack initiation [9]:

m f ) ' (   



  c f f b f N N ) 2 ( ' 2   



(4)

2

E

where  is the true strain range, m is the mean stress and E, f’, f’, b and c are

material parameters described in previous sections.

Fmax=880 k N

F

rigid

time

bolt

bar

F min =88 k N

c)

b)

a)

force F

Figure 6. Numerical model (a), initial crack (b) and loading pattern (c)

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