PSI - Issue 50

S.V. Panin et al. / Procedia Structural Integrity 50 (2023) 220–227 S.V. Panin et al. / Structural Integrity Procedia 00 (2023) 000 – 000

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Fig. 3. The macrostructure at the interface cross-sections of the welded joints obtained using the USW modes according to Table 1

To discuss the relationship between the USW parameters and the stress – strain diagrams, the authors used the weld joint thicknesses before and after the USW process (Fig. 1, b) in addition to the cross-sectional micrographs. Particular attention was paid to the following structural aspects: the integrity of the central (reinforcing) layer (prepreg), which included unidirectional fibers in the PEEK-based binder, as well as the residual thickness of both adhesive ED films, which was melted and partially extruded from the fusion zone during the USW process. Additionally, it was noticed that the strain response of the samples was affected not only by the structure at the interface between the layers. The lap welded samples experienced twin macrobending due to the doubled thickness (and an increased rigidity) of their central part. As a result, a crack had initiated by both interlaminar shear and normal delamination mechanisms. If the fusion zone formation was accompanied by partial fracture of the prepreg,