Assessment of Adhesive Bonding for Structural Design With Thick Adherends

The research programme reported herein explores high performance engineering adhesives in joining relatively thick adherends for lightly loaded structures, particularly those in ships and marine construction. With the original design requirements for conventional structures in mind, the assessment approach for bonded connections is based on experimental and theoretical techniques. The design engineer has very little understanding of adhesives and adhesion. A necessary review to this subject is therefore presented. The behaviour and design of adhesive joints and bonded structures are reviewed and areas of particular concern in adhesive and adhesive joints are highlighted. Twelve types of structural epoxy adhesives were used in this investigation to select a hot curing adhesive for bonding steel to steel adherends and another for bonding steel to glass reinforced plastic (GRP) adherends and also to evaluate bonding processes. The selection processes were aided by specially formulated experiments for small mechanical test specimens. The experiments included strength, durability in a wet environment and thermal creep aspects. A series of experiments for larger specimens has been developed around representative elements of skin/stiffener joints to establish a design basis for replacing fillet weld and bolted connection in steel and hybrid steel/GRP constructions respectively. These experiments included the static and impact performances and the fire resistance of thermally insulated hybrid steel/GRP panel. Meanwhile, development of prototype bonding process was established for large steel and steel/GRP panels using standard fabrication equipment for surface preparation, clamping and heat curing. Finite element methods were used to assess the failure in bonded joints due to cleavage tensile stresses and to correlate between small and larger joints in order to assess the local failure in bonded structure. The overall behaviour of bonded structures under lateral loading was also studied using a theory modified from composite beam and plate theory. These theoretical techniques proved to be effective in predicting the failure and behaviour of bonded structures which form a useful basis for design. Visual examination of failure surfaces of bonded joints was used to support the analyses. Significant results of this work include: (I) epoxy structural adhesives can provide effective structural connections in thick adherend applications, replacing welding and fasteners in some configurations, (ii) adherend type, stiffness and surface preparation significantly affect the strength of adhesively bonded joints and (iii) a bonded structure can be markedly different in behaviour (stiffness and strength) from its welded equivalent