PSI - Issue 47

J.P.M. Lopes et al. / Procedia Structural Integrity 47 (2023) 48–55 Lopes et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Compared to the basis geometry ( t P2 =1 mm), the percentile improvements for increasing t P2 up to 4 mm were 81.2%, 197.8% and 403.7%. This evolution is noteworthy and it can be justified by the reduction of peak stresses by increasing t P2 , added to the adhesive’s ductility, which absorbs peak stresses . In fact, the adhesive is able to plasticize when the yield stress is reached, leading to redistribution of stresses and higher loads transmitted at P m . The CZM P m predictions revealed a good correspondence to the experiments. P m was under predicted for t P2 =1 mm (by 4.3%). For all other t P2 , P m was slightly over predicted, with differences of 2.2% ( t P2 =2 mm), 4.5% ( t P2 =3 mm) and 3.5% ( t P2 =4 mm). In view of these results, it is confirmed that the CZM approach can be used for the numerical parametric study that follows. 3.2. Peel and shear stresses The distribution of σ y and τ xy stresses was firstly obtained along the adhesive length. In the following graphs, normalized σ y and τ xy stresses are represented ( σ y / σ avg and τ xy / σ avg , respectively). σ avg represents the average σ y over the adhesive length. In the abscissa axis, the normalized length x / l was considered, which was obtained by dividing the position of the adhesive layer by the total length. Fig. 6 shows  y stress distributions of the three adhesives in the adhesive layer as a function of l – (a) 10 mm and (b) 40 mm. For all the adhesives, σ y stresses are maximum at x / l =0, due to the transversal deformation of the base adherend allied to the high stiffness of the T component, leading to adherends’ separation at the overlap tips. At x / l =0.8, there is a small stress increase at the beginning of the radius, caused by the different stiffness of the components, but only for higher l , such as l =40 mm in Fig. 6 (b). Between adhesives, σ y stresses are maximum for the stiffer adhesive, i.e., the AV138. For this adhesive, σ y / σ avg peak stresses reached 83 and 192 for l =10 and 40 mm, respectively. These values progressively diminish by reducing the adhesives’ elastic compliance, up to reaching minimum values for the 7752 (26 and 57 for l =10 and 40 mm, respectively).

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σ y / σ avg

σ y / σ avg

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0

0

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

x / l AV138 2015 7752

x / l AV138 2015 7752

a)

b)

Fig. 6.  y stress distributions in the adhesive layer for l =10 (a) and 40 mm (b).

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τ xy / σ avg

τ xy / σ avg

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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

x / l AV138 2015 7752

x / l AV138 2015 7752

a)

b)

Fig. 7.  xy stress distributions in the adhesive layer for l =10 (a) and 40 mm (b).

Fig. 7 shows  xy stress distributions in the adhesive layer for the joints bonded with the three adhesives as a function of l – (a) 10 mm and (b) 40 mm. The behavior of  xy stress is very similar to  y stress, although with smaller magnitude due to the predominant peel load.  xy stresses are highest at x / l =0, due to the shear slide between adherends. At x / l =0.8