Avaliação da influência da espessura de adesivos estruturais em juntas metálicas com diferentes preparações superficiais

Abstract

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.