Crack Paths 2012

E X P E R I M E N TR AE SLU L T S

The photos shown in Fig. 2 are an example of the typical morphology of interior crack

initiation for V H C Fregime of TT180specimens subjected to R B loading, for which the

dimensions are: 2ainc=35.3Pm, 2aFGA=66.3Pm, and 2afisheye=206.2Pm. Since R B loading

leads to the largest stress at specimen surface, the crack initiation of fish-eye almost

formed underneath the surface and grew towards the surface then transformed into the

next stage of crack growth. For U L fatigue of axial loading, the sites for interior crack

initiation were almost randomly distributed in the cross-section.

surface

a

b

Vmax=808

Figure 2. S E Mphotos showing fractography of a TT180specimen (RB-4),

MPa, Nf=1.79u10 7; (a) crack initiation region with whole fish-eye morphology, and

(b) enlargement showing F G Asurrounding the crack origin.

123400

T T 1 8 0RB, SInut r 5 UL u T 5 U I t N u m b eorf Cyclesto Failure

700

750

800

850 900 950

178901200

180 RB, F G A 180 RB, Fisheye

150 UL, F G A 150 UL, Fisheye

Estimated value:

'KFGA=5.5MPa*m1/2

104 105 106 107 600

108

109 1010

M a x i m uStmress, M P a

Figure 3. Fatigue test results for two

Figure 4. F G Aand fish-eye sizes versus

groups of specimens.

applied maximumstress.

Table 1 lists the measurement data of the characteristic dimensions for crack

initiation of the two groups of specimens together with the values of the applied

907