Fatigue Crack Paths 2003

E l a v l E Z a V Z

Figure 2. Componentof stress in

Figure 1. Uniformdisplacement

polar coordinate‘

load condition.

F O R M U L A TOIFOT NH EP R O B L E M

As already done in several papers, the general problem of investigation of the stress

field in dissimilar media can be approached by eigenfunction [1] to determine the

singularity character of the extensional stress near crack tip.

Starting from a short crack length departing from a free edge, it has been simulated a

crack growth by artificially cutting the material with a very thin blade, Whose stress

singularities have been analysed in all steps and finally stress intensity factor was

evaluated. In this work it has been determined also the crack length at which the stress

field is too different from that of homogeneoussemi-infinite plates, represented by

Irwin equations [2]:

1

19

19

319

19

19

319

O'XI

-K1-cos—-1 — s e n — - s e n——K H - s e n —2-+ c o s — ~ c o s——o'0

\IZIr-r

2

2

2

2

2

2

1

19

19

319

19

19

319

(l)

O'yI

~ K I ' C O S —l + s e n — - s e n+—K H - S € n — ' C 0 S — ' C 0 S —

V27r-r

2

2

2

2

2

2

1'

I 1 xy 1211-1

- K 1 - s e n 2 - c o s Q - c o s fi + K H - c o s 2 l — s e n é ~ s e n fi

2

2

2

2

2

2

and the dependence of this critical length on the geometry aspect ratio a/hl (Fig. 2) is

also investigated. To do this we have considered three different configurations of

bimaterial joint with three different h1/h2 value: 1/3, 1, 3. For all geometry, w h e na/hl

I1 the stress field can be expressed according with K.Y. Lin e J. W. Mar[3]. The use of