Comparative study of the effects of galvanic corrosion on the strength and the failure of aluminium and stainless steel bolted joints

Abstract

This paper investigates the effects of bimetallic insert on corrosion, material degradation, loading capacity, stress distribution, strain distribution and failure of aluminium-stainless steel lap shear bolted assemblies. The single bolt lap shear assemblies of aluminium and stainless steel plates were performed in two settings in one of them a bimetallic insert was used. Considering that the aluminium plays the role of sacrificial anode in the aluminium-stainless steel galvanic couple, a single bolt lap shear assembly joining two aluminium plates is also considered as a reference. The experimental measurements were determined by tensile-shear testing method for three different conditions: dry condition and two corrosion states corresponding to 6 weeks and 16 weeks of accelerated corrosion tests. To support understanding of the effects of preload and friction changes due to the formation of corrosion products, finite element simulations were performed with varying preloads and friction coefficients. The study demonstrated significant effects of corrosion on loading capacity, bolt rotation and failure mode. The tensile-shear forces measured for the aluminium-aluminium assembly and aluminium-stainless steel assembly after 6 weeks of accelerated corrosion tests increased compared to the tensile-shear forces measured in dry condition. The increase in tensile-shear forces was related to the formation of corrosion products, affecting the preload and the frictional behaviour of the contacting surfaces. In agreement with experimental observations, finite element simulations demonstrated an increase in the tensile-shear force with the increase of frictional forces. The application of bimetallic inserts considerably reduces the effect of corrosion on the measured tensile-shear force of corroded assembly compared to non-corroded assembly. However, it affects the force-displacement response and failure mode compared to the response of aluminium-stainless steel assembly without bimetallic insert due to its effects on the bolt rotation and stress distribution. This needs to be considered in the design of dissimilar material bolted assembly.