Crack Paths 2012

The fracture resulting from the tests is the cup-cone type, with the special feature of

the threads which generate a fracture surface more asymmetrical, where the one thread’s

height must be surpassed (Fig. 4). On such a surface, there emerged a fibrous zone,

smaller than that in simple tension (compared to the total surface of the fracture), as

well as a more irregularly shaped external ring.

Figure 4. Fracture surface in bolt under monotonic loading.

Fatigue Tests

R-ratio

Wöhler curves were obtained (max-Nf and -Nf) for specimens with bolted joints

subjected to a cyclic load, for constant

and several values of the R-ratio (0, 0.25 and

0.50). They appear in Fig. 5.

700

700

45600

45600

( M P a )

( M P a )

m a x

12300 104

R =00.2550

105

106

R = 0

R=0.25

R=0.50

104

105

106

Nf (cycles)

12300

Nf (cycles)

Figure 5. Wöhler curves:

Vmax-Nf

(left) and 'V-Nf (right).

It can be seen that

max-Nf curves moveto the right whenthe R-ratio increases, whereas

the -Nf curves move to the left. Therefore, fatigue is a biparametric phenomenon,

where the increase of

max or decreases fatigue life. Furthermore, a potential fit was

obtained for the fatigue life, and was the same for all curves, considering both parameters,

1 4 1 2.82 V V '

(1)

2.8210 ˜

f N

max

524