Accelerated curing of adhesively bonded G-FRP tube connections-Part I: Experiments

In the wake of the industry-wide trend towards lightweight construction, fibre-reinforced polymers (FRP) gradually established as an alternative to traditional materials. They are used in particular when low weight, high strength or high corrosion resistance is required. For joining FRP components, adhesive bonding is increasingly preferred to mechanical fasteners as poorer transfer of loads resulting from interrupted fibres represents problematic. Despite all the technical advantages, adhesive bonding remains a comparatively slow joining process that is usually bound to limited manufacturing temperatures. This article shows, by means of experimental investigations performed on bonded FRP tubes, that curing by inductive heating of the adhesive bond can compensate for both disadvantages. For that, particles susceptible to electromagnetic fields (EMF) were added to two adhesives, a two component epoxy (2 K-EPX) and polyurethane (2 K-PUR), and the effect thereof on the adhesive was assessed. The particles consisted of Curie material (Curie particles, CP), which relieved all requirements regarding temperature control during the induction process. Subsequently, G-FRP single lap tubular joints (SLTJ) were assembled, cured following different protocols, and subjected to tensile tests. During the process, curing temperatures were monitored using appropriate measuring techniques. Mechanical testing showed that inductively cured SLTJ achieved equal or higher shear strengths, if compared to reference sets cured following the instructions given by the adhesive manufacturers. The results showed that adhesive type as well as curing conditions, in most cases had no significant influence on joint strength, which was verified by means of an analysis of variance. Summing up, inductive heating using CP proved effective in controlling temperatures without any external control, and yielded very high joint strengths with a reduction in curing time by the factor of 100 for the epoxy and 1400 for the polyurethane.

Automated summary

The article demonstrates that inductive heating of adhesive bonds with Curie particles can effectively control temperatures without external control, resulting in very high joint strengths with significantly reduced curing times.