Issue 39

M. A. Lepore et alii, Frattura ed Integrità Strutturale, 39 (2017) 191-201; DOI: 10.3221/IGF-ESIS.39.19 196 The stress increment processed in FE iterations is equal to   n n n n n n n n dD D K K d d d K 0 0 0 1 ,   0 ,   0                (11) s d d 0    n d d 0    (12)   s s s s s s s s dD D K K d d d K 0 0 0 1 ,   0 ,   0                where       n n n n max n n n f f d dD f d otherwise 2 1 ,   , 0 0 0,                               (13) s dD d 0   A null derivative of damage with respect to separation  n implies that damage is considered constant and equal to the last estimated value when opening displacement at the interface is decreasing or   n <  max . For this reason, if the current value of normal separation is less than previous  max , the corresponding point (  curr ,  curr ) is located inside the area under the effective limit curve and the damage D is considered unchanged (Fig. 5). The stress field is calculated using Eqs. (6)-(7).   n   max ( t )   curr ( t )   curr  f (  max )  K curr  K 0  d  d  n  P 1  P 2  P i  P n  d  d  n  Figure 5 : Interpolated cohesive law – closing of the interface.