Effects of accelerated ageing on the mechanical properties of adhesive joints between stainless steel and polymeric top coat materials for marine applications

Abstract

The performance of stainless steel brackets, adhesively mounted with a soft polyurethane-based accelerated 1-component adhesive onto completely coated steel substrates, is investigated. The investigated joint connections on typical marine top coats, namely polyurethane, polysiloxane and epoxy, exhibited a high mechanical stability even after accelerated ageing (salt spray exposure, cyclic temperature variations, high relative humidity). Tensile strength and shear strength criteria for a designed loading capacity of 50 kg were achieved with a safety factor of >10. All failure strength values were lower than the adhesion strength of the coatings to the steel. The adhesive material maintained its high deformability after ageing. The torsional rigidity of the adhesive joint exceeded the required clamping torque of the designed bolt. A cyclical lifetime of >9·106 load cycles was estimated. Effects of cyclic ageing on the creep performance of the adhesive joint were found to be insignificant. All adhesive joint connections met the requirements for a safety factor for the design for marine applications. Under sealed conditions, the ingress of moisture and chloride was avoided, and deterioration mechanisms typical for unsealed joints in marine environments (e.g. moisture penetration, adhesive material plastification, interfacial delamination) did not take place. Effects of mechanical and structural parameters as well as surface parameters of the top coat materials on the performance of the joints were statistically insignificant.