Impact of Shoprimer and Marine Ageing on Fracture Integrity of Structural Adhesive Joints with Naval Steel

Abstract

[Abstract]: This study characterises the Mode I fracture behaviour of naval steel joints bonded with a structural acrylic adhesive applied directly over water-based shoprimer, which allows reducing the necessary surface preparation. Accelerated ageing tests were performed on primed test specimens to evaluate durability under marine environmental conditions. The mechanical properties and fracture behaviour of an acrylic adhesive bonded to naval steel substrates were investigated under three conditions: bare steel, primed steel and aged primed steel. Tapered double cantilever beam (TDCB) specimens were tested under Mode I loading conditions. A data reduction scheme based on the equivalent crack length, known as the Compliance-Based Beam Method (CBBM), modified for steel substrates, was used to determine the fracture energy without requiring visual monitoring of crack propagation, making it particularly suitable for high ductile adhesives. Additionally, a numerical model was developed in ABAQUS to validate the proposed fracture characterisation methodology by comparison with the experimental response of the reference bonded joint. Accelerated ageing tests were performed to evaluate the long-term durability of the adhesive bonds. The tests showed cohesive failure modes in all cases, with different load capacities and fracture energies for specimens without and with the protective coating. Furthermore, an increase in fracture resistance relative to primed joints was observed in the aged specimens induced by moisture absorption. The results obtained demonstrate that the use of shoprimer requires specific surface preparation to ensure proper bonding. The main innovation of this study lies in validating the proposed fracture characterisation methodology for highly ductile adhesive joints and in the experimental assessment of the effect of direct adhesive application on primed naval steel surfaces.