Fatigue Crack Paths 2003

N U M E R I CSAILM U L A T I O NFF A T I G UCE R A CGKR O W T H

For the numerical simulation of fatigue crack growth under plane Mixed Mode-loading

several Finite-Element and Boundary-Element programs do exist. Within the scope of

this paper the program FRANC/FAM,whose program architecture is illustrated in

Figure 7, will be presented. In this program system the fatigue crack growth is realised

by an incremental crack propagation, which is controlled by the stress intensities at the

crack tip. The program takes into account the crack growth rate curve da/dN = f(ΔKV)

as well as the fracture mechanical limits ΔKth and ΔKC [9-11].

GEOMETRY,DESIGN

M A T E R I A L PROP T ES SERVICE L O A D B O U N D A R Y CONDITIONS C O N T R O L D A T A

F R A N C / F A M

initialmesh,thicknes, s rter cracks

FINITE- E L E M E N T ANALYSIS Fmax, R

E,ν, Rp0.2, ΔKth, ΔKIc a, C, m

da/dN(ΔKv), ac

vx,vy

Nend,Nmax, Δa0

A U T O M A T I C A D A P T A T I O N O FT H EF EM E S H

P R E P R O C E S S I N G O S T P R O C E S I N G S I M U L A T I O N

F R A C T U R E

M E C H A N I C A L

E V A L U A T I O N

STRESSESA N D STRAINS

F R A C T U RME C H . PROPERTIES

G E O M E T R Y D A T A

F A T I G U E D A T A

σij, σv, ux, uy

KI, KII, Kv, ϕ0

coordinates of c ack tip(s)

ΔKv(a), a(N), N p ,

Figure 7. Finite-Element program for the simulation of fatigue crack growth.

The first simulation example for this program is a knee-lever, whose loading with a

cyclic force F(t) and displacements restraints can be gathered from Figure 8a. If only

crack (a) is located in the knee-lever, this crack sharply kinks at the beginning of the

simulation. In the following the crack grows slightly curved towards the border (Figure

8b). Before the kinking of the crack, a Mixed Modeloading situation with a high Mode

II-portion at the crack tip is given. This high Mode II-portion is reduced during the

simulation, before it increases again in the very near of the border. If only crack (c) is

located in the knee-lever, the crack path shown in Figure 8c will develop. At the end of

the simulation the knee-lever fails by instable crack growth under pure ModeI-loading.

If otherwise all three cracks (a), (b) and (c) are arranged in the knee-lever, so only crack

(b) and crack (c) will grow, whereby the shortest crack (b) is subjected to the highest