Issue 42

M. Peron et alii, Frattura ed Integrità Strutturale, 42 (2017) 214-222; DOI: 10.3221/IGF-ESIS.42.23 219 define the SED parameters, then the hypothesis that the material has a brittle behavior is valid and in the crack case (the control volume is a sector centered at the notch tip, Fig. 2.b) the strain energy density can be express through eq. (3). 1 2 2 2 1 2 2(1 ) 2(1 ) I II c c e K e K W E R E R       (5) The authors proposed the following approach: the control volume remains the same in all load configurations and it’s equal to the control volume defined under pure mode I: in this way it’s possible to recalculate the value of the critical strain energy density in mixed mode I+II and in pure mode II. Under this hypothesis, the scatter band is contained between ± 10 %, as it seen Fig. 3.c. In Fig. 3 the error is calculated using the W c defined through the σ t tension; the W c can be redefined through the mean value of the strain energy density of each specimens. The new values of W c are listed in Table 5 : the errors using these values of critical energy density are presented in Fig. 4; except Necuron 301, the scatter band is contained between ± 15 %. Density [Kg/m 3 ] R c [mm] W c [MJ/m 3 ] 100 0.20 0.140 145 0.24 0.111 300 1.0 0.039 708 0.62 0.21 Table 6 : New values of critical energy density that fit better the results. Figure 3 : Ratio between the predictions of maximum loads and experimental loads: a) notched specimens, b) ASCB specimens under mixed mode, c) personal approach for ASCB specimens under mixed mode, d) all notched specimens under mode I.