Issue 47

S. Bressan et alii, Frattura ed Integrità Strutturale, 47 (2019) 126-140; DOI: 10.3221/IGF-ESIS.47.10



K

ε

σ 1.50 (2 )



 0.58 



0.087

f

NP

U

(17)





N

N

0.59 2

f

f

E

2

The results of the application of K f

on I-S model are shown in Fig. 10 and Fig. 11.

Figure 8: Life evaluation of 6061Al employing I-S parameter modified with K t,n .

Figure 9: Life evaluation of 316LSS employing I-S parameter modified with K t,n .

Figure 10: Life evaluation of 6061Al employing I-S parameter modified with K f .

Figure 11: Life evaluation of 316LSS employing I-S parameter modified with K f .

The results related to high values of K t,n are sensibly improved for 6061Al. Failure life data are well correlated in the factor of 2 band. In case of 316LSS, there is a general overestimation of failure life in the case of PP loading. Non-proportional loading data are well correlated except for K t,n =1.5. Crack initiation site has been also taken into account in life evaluation. As described in the section 3.2, the cases where crack initiation site has been detected away from the notch tip are limited. Specifically, the influence of this phenomenon on life evaluation has been considered only for the 316LSS specimens with K t,n =1.5 and 2.5. In order to take into account the crack initiation site, a FEM analysis has been conducted on the considered specimens. The same stress recorded in the experimental tests conducted on the notched specimens has been applied as a tensile stress of a static linear analysis. The local stress occurring at the same location where the crack initiated σ' loc has been obtained. The distance of the crack initiation spot from the tip has been obtained by observing the fracture on the tested specimens. A new stress concentration factor K’ t has been evaluated as the ratio between the local value of stress and the nominal stress σ N already defined [39].

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