Abstract
Research and/or Engineering Questions/Objective For developing lightweight structures, it is required to design structures with mixed materials joined with adhesive joining. Fasteners are used as a secondary joining method to hold the assembly together during adhesive curing. Combination of adhesive joints and fasteners in same joint is called as hybrid joint. Since fasteners are only used to hold the assembly together, it is required to find out if fasteners contribute to lap shear strength of hybrid joints. Also, effect of fastener spacing on hybrid joint strength needs to be investigated to reduce manufacturing cost. Compatibility of different fastener types on overall hybrid joint manufacturing needs to be found out. Methodology: An experimental study was carried out using hybrid, adhesive and fastened lap shear joints. The base materials consists of 4.8 mm thick aluminum 6061 T6 joined to 1 mm thick high strength steel. A new wide specimen was designed with 120 mm width so as to accommodate variable fastener spacings of 30 mm, 60 mm and 90 mm. Two different types of fasteners such as Magna-Lok and Flow Drill Screw (FDS) were used to manufacture hybrid joints. One part heat cured structural epoxy adhesive was used in hybrid joint. All the joints were tested in static loading and force vs. crosshead displacement data was obtained. The difference of hybrid joint manufacturing process while using Magna-Lok and FDS was studied. Results Hybrid and adhesive joint lap shear strength are similar. So there is no benefit to use fasteners along with adhesive joints under shear loading and number of fasteners in hybrid joints should be minimized to save cost. The fastener spacing has no effect on hybrid joint lap shear strength. The lap shear strengths of hybrid and adhesive joints have significantly higher strengths than fastened joints. The fastener type does not contribute in hybrid joint lap shear strength. However, the assembly process with Magna-Lok and FDS is different while using with adhesive in a hybrid joint. It was challenging to use FDS while using with adhesive in hybrid joint for selected base materials and thicknesses. Limitations of this study Fastener spacings beyond 90 mm are not investigated in this study as the width of the lap joint is limited to 120 mm. Lap shear joints beyond 120 mm width are difficult to test under tensile loading in universal testing machine. What does the paper offer that is new in the field including in comparison to other work by the authors? The experimental work involves joints manufactured with dissimilar base materials, FDS and Magna-Lok fasteners with variable fastener spacings and adhesive joining. All these variables studied together in hybrid joints is new. The specimen design with elimination of fastener interaction with adhesive peel stress is new. Conclusions Fasteners do not contribute in hybrid joint lap shear strength. Fastener spacing up to 90 mm does not have any impact on hybrid joint lap shear strength. Therefore, the number of fasteners in hybrid joint assembly should be minimized to save cost. It was challenging to use FDS in hybrid joints to join aluminum to high strength steel.