Abstract
The paper studies the adhesive strength of aluminum alloy specimens bonded with the use of an epoxy adhesive, under the tensile-shear stress state, depending on the testing temperature. Tension of modified Arcan specimens with load angles of 0, 22.5, 45, 67.5, and 90° with respect to the plane of adhesion is chosen as the experimental method. Experiments were performed at temperatures of −50, +23, and +50 °С. The analysis of the obtained results yields a linear fracture criterion and a fracture locus for the adhesive failure strain energy density, which takes into account the ratio of the elastic properties of the adhesive to those of the substrate. The region bounded by the fracture loci of adhesive strength and ultimate strain energy density determines the conditions for the safe loading of the bonded assembly in terms of the energy and force criteria of adhesive failure. The proposed fracture loci can be used, preferably simultaneously, to estimate the in-service strength and reliability of adhesively bonded assemblies.
Highlights
I n designing advanced machinery and predicting its further development there is a consistent trend of increasing external mechanical, thermal and other loads and maintaining performance and durability under extreme operating conditions, including emergency situations
The approach using the strain energy release rate Gc to characterize adhesive failure is widespread [15, 16]. (The strain energy release rate Gc is defined as a decrease in the total elastic energy in the specimen per unit specimen width with an infinitesimal increase in the delamination length.) It was experimentally found that the ultimate values of Gс at fracture are different for cleavage and shear (GIс and GIIс, respecrively); to predict the values of Gс for mixed loading conditions, when the normal n and tangential t stresses act simultaneously, J
Modified Arcan specimens with glued inserts have been used to study the effect of the stress state on the adhesive strength of a 1570 aluminum-magnesium-scandium alloy assembly bonded with ED-20 epoxy resin cured with polyethylene polyamine
Summary
I n designing advanced machinery and predicting its further development there is a consistent trend of increasing external mechanical, thermal and other loads and maintaining performance and durability under extreme operating conditions, including emergency situations. In the engineering specifications for adhesive materials there is information only on ultimate shear strength (less frequently on cleavage strength) and mostly at room temperature This prevents making adequate design calculations of the strength of coatings and adhesively bonded assemblies in operating structures and mechanisms, with the use of advanced CAD/CAE systems. (The strain energy release rate Gc is defined as a decrease in the total elastic energy in the specimen per unit specimen width with an infinitesimal increase in the delamination length.) It was experimentally found that the ultimate values of Gс at fracture are different for cleavage and shear (GIс and GIIс, respecrively); to predict the values of Gс for mixed loading conditions, when the normal n and tangential t stresses act simultaneously, J. The tension+shear loading pattern is fairly widespread in practice and the most dangerous for the structural integrity of an adhesive assembly, when the angle between the normal to the bond line and the resultant of forces (external and gravity) is at most 90°
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