Issue34

R. Brighenti et alii, Frattura ed Integrità Strutturale, 34 (2015) 59-68; DOI: 10.3221/IGF-ESIS.34.05 64 1 40 Young modulus ratio , E f /E m 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Dimensionless SIFs, K* IIr (a) l / L f =0.1 num. data 2L f /  f 20 40 80 5 10 15 20 25 30 35 l / L f =0.7 1 40 Young modulus ratio , E f /E m 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Dimensionless SIFs, K* IIz num. data 2L f /  f 20 40 80 5 10 15 20 25 30 35 l / L f =0.1 l / L f =0.7 (b) Figure 4 : Dimensionless radial and longitudinal Mode II SIF, (a) , II r K and (b) , II z K , vs Young modulus ratio, f m E E , for different values of fibre aspect ratio, 2 f f L   , and relative debonded length equal to 0.1 and 0.7. 0 0.2 0.4 0.6 0.8 1 Relative crack length, l/L f 0.0 0.1 0.2 0.3 0.4 Dimensionless SIFs, K* Ir (a) L f /  f = 80 num. data interpol. E f /E m 1 10 25 40 0 20 40 60 80 100 Fiber aspect ratio , 2 L f /  f 0.0 0.1 0.2 0.3 0.4 Dimensionless SIFs, K* Ir (b) E f / E m =10 num. data interpol. l /L f 0.05 0.20 0.50 0.90 Figure 5 : Dimensionless radial and longitudinal Mode II SIF, (a) , II r K and (b) , II z K , vs Young modulus ratio, f m E E , for different values of fibre aspect ratio, 2 f f L   , and relative debonded length equal to 0.1 and 0.7. / , i m cg i i th i IC v dl dN C K K K K         (9) In Eq. (9), , i i C m are the Paris constants of the interface, l is the debonded length (Fig. 1b), and i K  is the equivalent stress intensity factor range produced by the cyclic remote stresses. The above crack growth rate takes place in a thin weak layer placed between two different materials. Such a layer can be considered as a third material whose properties are themselves affected by the fatigue process. For the above reason, the interface crack propagates in such a degraded material, and a suitable evaluation of the damage can be done by using Eqs. (4) to (6). In the present study, the above biaxial damage evaluation is applied to the Paris constant i C : 0 , ( ) / (1 ) i i f i C N C D   , where 0 i C is the undamaged initial constant value. The critical detached length, c l , and the corresponding number of loading cycles, c N , leading to such an ultimate condition can be evaluated as follows: (b) (a) (a) (b)