PSI - Issue 3

F. Berto et al. / Procedia Structural Integrity 3 (2017) 85–92 F. Berto et al./ Structural Integrity Procedia 00 (2017) 000–000

90 6

it seems that the phase displacement could increase or vice versa decrease the fatigue life of the component as a function of the notch geometry.

600

Torsion R=-1 Tension R=-1

Multiaxial R=-1  =1  =0° Multiaxial R=-1  =1  =90°

Nominal stress amplitude [MPa]

60

1.00E+04

1.00E+05

1.00E+06

1.00E+07

Number of cycles to failure, N

Fig. 3. Data from multiaxial tests from V-notched specimens.

4. A synthesis in terms of linear elastic SED averaged over a control volume The averaged strain energy density criterion (SED) states that brittle failure occurs when the mean value of the strain energy density over a given control volume is equal to a critical value W c . This critical value varies frommaterial to material but does not depend on the notch geometry and sharpness. In the particular case of 40CrMoV13.9 steel the radius of the control volume ( R c ) has been found to be equal to 0.05 mm. Dealing with V-shaped notches the control volume is defined as is visible in Fig. 4a, the volume assumes a crescent shape and it is centred at a distance equal to r 0 from the notch tip. The distance r 0 depends on the radius of the notch  and on the notch opening angle 2  . 2 2 q      (1)

0 1 r q q  

(2)



For semicircular notches under mode I and III loadings, the volume assumes the crescent shape shown in Fig. 4b, where R c is the depth measured along the notch bisector line. The outer radius of the crescent shape is equal to R c +  /2, being  /2 the distance between the notch tip and the origin of the local coordinate system.

2  

 

 

R c  /2

R c r 0

R c +r 0



(b)

(a)

Fig.4. Critical volume for (a) V-shaped notches and (b) semicircular notches.