Issue 18

S. Marfia et alii, Frattura ed Integrità Strutturale, 18 (2011) 23-33 ; DOI: 10.3221/IGF-ESIS.18.03 29 - Interface  3 0 0 270 N/mm 0.5 4.7 MPa 0.34 N/mm N T N T cN cT K K G G           (31) where 1 E , 1  , 2 E and 2  are the Young modulus and the Poisson coefficient of the body 1  and 2  , respectively. In particular, first a simple tensile test is performed to show how the response of the interface can be significantly influenced by the damage occurring in the body 1  . Then, the maximum detachment force is evaluated for different values of the adhesion lengths and of the initial values of the body damage. Tensile test The geometry and loading condition of the scheme considered to perform the tensile test are shown in Fig. 2. The geometrical parameters are 500 mm 49 mm b h   and an unit thickness is adopted. Figure 2 : Scheme of the uniaxial test. In order to investigate the influence of the damaging behavior of the body 1  on the tensile mechanical response of the interface and, as a consequence, of the whole structure, three analyses are developed considering different values of the initial threshold damage strain 0  and keeping constant the fracture energy c G ; in particular it is set: Case 1: 0 0.00016   Case 2: 0 0.00026   Case 3: 0 0.00036   The three analyses are performed considering as interface model the two coupled damage approaches previously presented (Model 1 and Model 2). In Fig. 3 and Fig. 4, the numerical response obtained adopting the Model 1 and the Model 2 are shown. The results reported in the graphics of these figures are plotted with a dotted line for Case 1, with a dashed line for the Case 2 and with a solid line for the Case 3. Furthermore, the average tensile stress is introduced as q   and the average strain in the body 1  is set as / v h    with v  the relative vertical displacement between the two opposite edges of the body 1  . The computations are performed adopting the arc-length technique and considering the relative normal displacement N s at the interface as control parameter. With reference to Fig. 3, it can be noted that in the Case 3 the mechanical response of the structure is strongly influenced only by the softening behavior of the interface as in this analysis the damage does not occur in the body. In fact, the tensile interface response is equal to the constitutive interface law and the body is subject to the elastic unloading when the interface starts to damage. In the other two cases, the tensile mechanical response of the structure depends on the coupling of the body and interface damage. In fact, after the achievement of the peak stress, which coincides with the tensile strength of the body, the softening branch depends on the evolution of the damage in the body until the interface damage, governed by the relative displacement, becomes higher than the body one at the interface. At this point of the analysis the softening tensile response is due to the development of the interface damage governed by the relative displacement. 2  1   b h h q  