PSI - Issue 83

R.J.B. Rocha et al. / Procedia Structural Integrity 83 (2026) 179–186

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in Table 3. Boundary conditions are defined in Fig. 3. All loading and support cylinders were represented as rigid analytical surfaces. The two lower support cylinders were fully constrained. The upper loading cylinders were subjected to a synchronized downward displacement of 40 mm, while horizontal motion and out-of-plane rotation were restricted. Contact interactions were defined between the rigid cylinders and the specimen contact regions. The finite element discretization employed structured quadrilateral elements for the adherends and a swept mesh for the adhesive layer. Increased mesh density was introduced near the overlap edges through biasing techniques. The adhesive layer was represented by a single cohesive element through its thickness.

Fig. 3. Finite element mesh and boundary conditions for SLJ (a) and SJ (b).

3. Results 3.1. Failure modes

Failure modes were determined through visual inspection of the fractured surfaces and classified as cohesive failure of the adhesive layer (AL) or adherend failure (AD). No interfacial adhesive failures were observed, confirming the effectiveness of the surface preparation. Representative photographs of the failed specimens are presented in Table 4. The failure mode was dependent on the joint geometry, L O , adhesive type, and adherend material.

Table 4. Examples of adhesive joint failures showing AL and AD failures.

L O (mm)

Material

5

10

20

SLJ

2015

PLA/

4 AL

4 AL

3 AL + 1 AD

PLA/ SJ

2015

3 AD + 1 AL

3 AD + 1 AL

3 AD + 1 AL

SLJ specimens were most susceptible to peel stresses caused by eccentricity. AL failure in the adhesive dominated at L O =5 mm and 10 mm for all adherend/adhesive combinations. At L O =20 mm, a transition to AD (or mixed) failure occurred, especially with the stiffer 2015 and PETG or ABS adherends. The more ductile 7752 presented predominantly AL failure even at the largest L O for the PLA adherends. This progressive shift explains the limited additional strength gain beyond L O =10 mm in SLJ configurations. SJ displayed intermediate characteristics. Failure