Resumo:
Structural adhesives have the ability to bond materials for a long time, withstand great
stresses and offer advantages over the most common joining methods, such as welding and
riveting, providing adhesive joints with excellent fatigue resistance. These adhesives are found
in industries with more advanced manufacturing processes, such as the automotive,
aerospace, electronics, naval, and civil construction industries. Efficient adhesives must wet
the surface, penetrating the surface imperfections of the material, thus promoting greater
adhesion between the parts and then hardening until becoming a single cohesively strong
solid. In view of this, the methodology used in this study sought to evaluate simple lap joints
with different thicknesses of 0.1, 0.25 and 0.5 mm in metal samples mechanically prepared
with sandpaper or Bristle Blaster, in order to identify the preparation mechanism that
enabled the best mechanical resistance to shear (lap shear). The results obtained by lap shear
were compared by the statistical method Tukey's test, the failure mode was characterized with
the aid of the ISO/DIS 10365:2020(E) standard and the fracture surfaces examined by scanning
electron microscopy. In addition, with the support of the PCA - Principal Component Analysis
statistical tool, it was possible to reduce seven variables (formulation, sample preparation,
adhesive type, classification, thickness, average and failure mode) to only two components,
representing 85.65% of the data, and clearly separate the adhesive types into well-defined
quadrants. The best average shear strength came from the samples with substrate prepared
by 360 and 600 sandpaper with 0.25 mm thickness of acrylic adhesive, and with substrate
prepared by Bristle Blaster with 0.1 mm thickness of epoxy. Regarding the failure mode,
cohesive predominance was observed in acrylics, and mixed or adhesive failure in the samples
with epoxy. In both cases, this profile was independent of the mechanical preparation
performed. In the micrographs of the fracture surfaces of the best performing samples, ductile
fracture was observed in the joint with 0.25 mm of acrylic adhesive and significant presence
of spherical voids and brittle fracture in the sample with 0.1 mm of epoxy adhesive. In both
formulations, no regions with absence of adhesive were identified.
