Investigation on ultimate strength and failure mechanism of bolted joints in two different aluminum alloys

• I performed experiments for bolted joints with two different aluminum alloys.
• Material properties, plate thickness, bolt array and end distance were main variables.
• Curling (out-of-plane deformation) occurred in joints with long end distance.
• The curling resulted in strength reduction.
• Failure mechanism and curling occurrence were different according to main variables.

Aluminum alloys have been utilized in various industrial fields and building structures due to high strength-to-weight ratio, increased durability, formability and enhanced service life. They can be classified into seven groups from 1000 to 7000 series according to alloyed chemical compositions except main pure aluminum component. Experiments of single-lap joints with 6061 type alloys were performed by Kim et al. and the results show that curling (out-of-plane deformation toward plate thickness direction) occurred in bolted joints with a long end distance and it is found that the curling influenced mechanical strength. In this paper, ultimate strength and failure mechanism of single shear sheet bolted joints fabricated with two different aluminum alloys; 6061-T6 (aluminum–magnesium–silicon series) and 7075-T6 (aluminum–zinc–magnesium–copper series), which are the most widely used materials due to the need of high strength were compared. Alloy type, plate thickness, end distance and bolt arrangement were considered as main variables. Monotonic tensile tests have been conducted for specimens and two fracture modes such as shear fracture and block shear fracture were observed. Some bolted joints with relatively thinner plate and longer end distance were accompanied by curling and the curling led to sudden strength reduction. The difference of material properties and plate thickness affected failure mechanism and curling occurrence. Moreover, strain distribution and curling deformation pattern against enforced displacement were investigated to grasp the curling effect on the behaviors of joints.