Issue 12

S. Marfia et alii, Frattura ed Integrità Strutturale, 12 (2010) 13-20; DOI: 10.3221/IGF-ESIS.12.02 16 the optimal adhesion length increases and also the maximum value of max F increases. While the first results is absolutely expected, the second one appears physically unacceptable, as it implies that more the support material is damaged greater values of the forces can be transmitted from 2  to 1  . This strange effect is due to the uncoupled damage evolution of the body and of the interface. Figure 3 : Decohesion force max F versus adhesion length, uncoupled damage model. T HE F REDDI -F REMOND MODEL he Freddi-Fremond (FF) model is based on the assumption of the following forms for the free energy and the pseudo-potential of dissipation of the domain 1  : (5) (6) where ε is the strain tensor,  and  are the Lamé parameters, w is the initial threshold energy, k is a parameter measuring the nonlocal effect, I and I  are the indicator functions of the sets   0,1 and   0,  , respectively, c is the viscosity parameter of damage, while the dot symbol  denotes the scalar product between two tensors, the superposed dot on the damage variable indicates the derivative with respect to the time. The free energy and the pseudo-potential of dissipation of the interface  are: (7) (8) where w  is surface Dupré energy, k  is a parameter measuring the nonlocal effect, I  is the indicator function of the set   , 0  ,  indicates the scalar product, N is the outward versor normal to the domain 1  in correspondence of the interface  , ˆ k  is the interface stiffness, , k   is the surface-domain interaction parameter and c  is the viscosity parameter of interface damage. Moreover, a further nonlocal interface effect is also introduced in the FF model. 0 50 100 150 200 250 300 350 400 450 0 50 100 150 200 250 300 350 400 adhesion length [mm] F max [N] D  =0.00 D I =0 D  =0.90 D I =0 D  =0.95 D I =0 D  =0.99 D I =0 T         2 2 1 1 1 2 2 2 D tr wD k D I D                     ε ε ε     2 1 2 c D I D                      2 2 1 2 2 2 1 , 1 2 1 1 ˆ 1 2 2 w D k D I D I D k k D D                           u u N u u     2 1 2 c D I D          