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Throughout the past, heating by electromagnetic induction has been frequently used to design speedier curing processes of adhesives. With this method, bonded components are exposed to an alternating electromagnetic field (EMF), which generates heat in EMF-sensitive adherends, like steel and aluminium, or in susceptors that are admixed to the polymers to be cured, e.g. fibres or particles. Recently, specially designed susceptors, so-called Curie particles (CP), have shown their great potential for induction curing. Heat generated in CP is capped by the materials Curie temperature (Tc), preventing the adhesive from overheating. As a result, curing proceeds way faster and independently from ambient temperatures, opening up new application fields for bonded components. Although practical applicability has already been demonstrated, CP-induced heating – and consequently curing – has proven to be very sensitive to the boundary conditions of the considered application. Therefore, induction times needed to achieve full cure must currently be determined by cumbersome and costly experimental investigations. To compensate for this disadvantage, the present study – representing the second part of a series – aimed at offering a first approach of a numerical model in which thermal and kinetic aspects of CP-induced accelerated curing were combined. For that, curing kinetics of two kinetically different 2K epoxy adhesives were linked to a transient heat flow simulation in Ansys based upon experimentally determined heat loads. Since the first part of this series concentrated on presenting all preliminary experimental work as well as analytics applied during modelling, this part focuses on the validation of the developed FEA using the exemplary application of CP-cured Glued-in Rod (GiR) specimens. In the following, various numerical parameter studies were carried out, demonstrating principal functionality of the new FEA technique and highlighting in particular its contribution for the design of more efficient and target-orientated CP-curing processes. [ABSTRACT FROM AUTHOR]

Accelerating the polymerisation of adhesives has been a long-established field of research in context of adhesive bonding technology as long curing times – sometimes up to days – represent a decisive disadvantage in contrast to most mechanical joining techniques like riveting or screwing. In addition to, e.g., curing via UV, microwave or IR radiation, electromagnetic induction represents a promising solution for speeding up the cure of polymers. With this method, adhesively bonded components are subjected to an alternating electromagnetic field (EMF) that induces heat in EMF-sensitive materials, e.g., steel or aluminium. If intrinsic EMF-sensitivity of the materials to be bonded is not given, different types of susceptors like meshes, fibres or particles are added to the adhesive in order to be heated inductively and thus cure the adhesive from the inside. Recent research has focused on a special type of susceptors, so-called Curie particles (CP), which can only be heated inductively up to their specific Curie temperature (Tc) at which CP-induced heating automatically stops. As a result, a curing process is created that eliminates the need for external temperature monitoring while simultaneously preventing overheating of the bond. As underlying curing kinetics – most importantly polymerisation enthalpy and curing time – significantly differ depending on the considered adhesive, induction times needed to achieve full cure must currently be determined through costly preliminary investigations on an experimental level. Thus, to contribute for a more efficient and controllable bonding process, the present study aimed at developing a numerical model based on the Finite Element Method (FEM) and capable of predicting the curing degree α in dependency of curing temperature profiles TCure(t) and the CP content ccp. For this purpose, the curing kinetics of two fundamentally different 2K epoxy adhesives were linked to a transient heat flow simulation based upon experimentally determined heat loads. The validation of the developed FEA technique was successfully carried out using the example application of inductively cured large-scale Glued-in rod (GiR) specimens, whereby experimentally determined temperature profiles showed excellent agreement with the numerical predictions. The present paper focused on presenting preliminary experimental work as well as all analytical methods implemented for the numerical modelling. [ABSTRACT FROM AUTHOR]

This last paper of a series of three concludes the analysis of a series of adhesively bonded tube-in-tube (TiT) joints composed of glass-fibre reinforced polymers (G-FRP) for which induction heating with Curie-particles (CP) was used to accelerate curing. It focuses on the prediction of their load capacity using a probabilistic method (PM). First, the G-FRP material was characterised with regard to transverse (tensile) and shear stresses, which allowed to determine a valid failure criterion, including the related statistical description subsequently required for the PM. Then, finite element analysis (FEA) was used to determine the stresses within the TiTs, for not only a perfect geometry, but also considering a series of possible geometrical imperfections (offset and misalignment of the centrelines, and ovalisation) with three degrees of severity. The influence of aforesaid imperfections on stresses was determined, and discussed. Based thereupon, load capacity was numerically determined, compared to the experimental values, and the influence of imperfections highlighted. Predicted joint capacities agreed well with the experimental ones. The influence of centreline offset and ovalisation was found to be of minor importance, if compared to that of the misalignment. By an extension of the procedure, scattering of the experimental data was also predicted in form of upper and lower quantiles, which also agreed well. [ABSTRACT FROM AUTHOR]