Experimental investigation of the mechanical behavior of aluminum adhesive joints under mixed mode loading conditions

Paper #:
  • 2018-01-0105

Published:
  • 2018-04-03
Abstract:
In recent years, structural adhesives have rapidly become the preferred alternative to resistance spot welding in fabricating stronger, lighter aluminum connections. These joints inevitably undergo and must withstand complex quasi-static and/or dynamic loads during their operating lifetime. Therefore, understanding how loading conditions affect the mechanical behavior of adhesive joints is vital to the advancement of structural safety and is worthy of thorough study. Quasi-static and dynamic tests are performed to analyze both the strength and failure mode of aluminum 6062 substrates bonded by adhesives (Darbond EP-1506) at different loading conditions. An Arcan test device, which allows for the application of mixed mode loads ranging from pure peel (Mode I) to pure shear (Mode II) to the adhesive layer, is employed in quasi-static testing. A self-designed, servo-hydraulic medium speed test machine is utilized to perform dynamic testing. To avoid severe system oscillations exhibited in force measurements during dynamic testing, the Arcan test device is replaced by a set of integrated fixtures to reduce fixture weight and improve stiffness. To induce different mechanical responses within the adherend and adhesive materials, the specimens are subjected to transverse and/or shear forces. Experimental results demonstrate that the fracture displacement increases with an increase in test angle of the applied force, indicating that ductile fracture predominates brittle fracture and is the governing mode of failure when shear loading is significant in mixed loading scenarios, especially for dynamic tests. Furthermore, dynamic strengthening is present in samples subjected to peel loading, but is absent in samples tested under mixed loading conditions, where interface failure is more likely to occur than cohesive failure. This observation reveals that the cohesive zone is reinforced by the strain rate effect, whereas the interface between the adhesive and adherend does not experience this phenomena.
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