Issue 37

M. Kurek et alii, Frattura ed Integrità Strutturale, 37 (2016) 221-227; DOI: 10.3221/IGF-ESIS.37.29

Therefore, the scatter can be determined as follows:

E

T 10 

(17)

Fig. 2 shows the relationship between the scatter value T and the angle  , for two selected materials.

0

-10

-20

-30

0.1261

B

K

-40

(a)

(b)

-50

-60

0

5 10 15 20 25 30 35 40 45

0

5 10 15 20 25 30 35 40 45  , o

 , 0

Figure 1: Dependence of the parameter B on (a) the angle  and (b) K value for 10HNAP steel.

25

10

(a)

(b)

9

20

8

7

15

6

T

T

10

5

4

5

X: 45 Y: 2.128

3

0

2

0

5 10 15 20 25 30 35 40 45

0

5 10 15 20 25 30 35 40 45

 0

 0

Figure 2: Relationship between the scatter T and the angle  for: (a) 10 HNAP steel [10]; (b) PA4 aluminum alloy [11].

Scatters are computed only for experimental tests under combined bending and torsion. The angle  corresponding to the minimum scatter value is registered for each examined material and listed in Table 1. The present authors propose a new expression for  :

   

   

   

   

a  

( 3 1 5.22 fi a N

)

   

 



arcctg

N

2

(

)

fi





(18)

4

where  is a function of the fatigue strength ratio 2 B  :

(

)

a  

N

a

fi



B

(19)

2

(

)

N

fi

225