PSI - Issue 41

M.R.M. Aliha et al. / Procedia Structural Integrity 41 (2022) 87–93 Aliha et al. / Structural Integrity Procedia 00 (2022) 000 – 000

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Fig. 3. FE model and boundary conditions of Bi-ASB specimen.

4. Results The variations of fracture parameters including the stress intensity factors (K I and K II ), T-stress (that is first non singular stress term ahead of crack tip), Biaxiality ratio (that is the ratio of singular terms over non-singular term), and the direction of fracture initiation or kinking angle relative to the crack line) are investigated in this section for the analyzed Bi-ASB specimens. Parts (a), (b), (c), (d), and (e) shown in Fig. 4 demonstrate how the adhering material types considered in the left and right sides of the Bi-ASB specimen can affect Y I , Y II , non-dimensional T stress (T * ), Biaxiality ratio (BR), and the direction of fracture initiation ( θ 0 ). T * and BR for the Bi-ASB specimen are determined from Eqs. (2) and (3), respectively. The position of adhering materials on the left and right sides of the adhesive affects the fracture parameters slightly, but Y I , Y II , and T * are sensitive noticeably to the type of adherent materials. Parts (a) and (b) of Fig. 4 show that Y II equals to zero for symmetric span supports conditions (i.e. S ′ = S), and therefore the Bi-ASB specimen is subjected to pure mode I loading. When the movable support span distance (S ′ ሻ becomes closer to the crack, mode II footprint appears in the Bi-ASB specimen, and Y I finally equals to zero when S ′ /L reaches a specific value of 0.04. In this condition, pure mode II condition occurs in the Bi-ASB specimen. Part (c) of Fig. 4 shows the variations of T * for the investigated Bi-ASB specimen. It can be seen that the T-stress is significantly negative for dominantly mode I conditions (i.e., higher S ′ /L values), whereas the corresponding value of T * tends to zero as the value of S ′ /L decreases (i.e. where mode II becomes dominant). According to the fracture mechanics literature for bonded components, if the magnitude of T-stress is large enough relative to the singular terms, the non-singular term can play a substantial role in mixed mode I/II fracture [9-12]. ∗ = 2 ( + ′ ) 3 ′ (2) In the process of mixed-mode fracture, the importance of the non-singular term relative to the singular terms (K I and K II ) is commonly characterized by a variable called Biaxiality ratio (BR) defined as: = √ √ 2 + 2 (3)