ABSTRACT

Glued-in Rods (GiR) are nowadays widely established as an adhesively bonded connection type in timber engineering. The assemblies consist of rods, e.g. threaded rods or rebars, made of steel, or Fibre-Reinforced Polymers (FRP), which are bonded into wooden construction elements. In contrast to mechanical fastening, adhesive bonding often results in a better load transfer between the adherends, and consequently a reduction of local stress peaks in comparison to mechanical fasteners. Bonding of GiR is typically performed with 2 K polyurethanes (2 K-PUR) or 2 K epoxies (2 K-EPX), for which full curing can last up to several days. Consequently, before the connection can be stressed, or moved for further processing, components have to be maintained in fixed position. This process can be very time, and cost, consuming for contractors. In order to create a speedier, thus more efficient, bonding process, the present study investigated accelerated curing of large-scale GiR specimens with the help of inductively heated Curie particles (CP). The CP are added to the adhesives, and exposed to a high frequency (HF) electromagnetic field (EMF). The EMF heats the mix up until the Curie temperature (T _C) is reached, at which point the heating automatically stops. Due to the generated heat, polymerisation is significantly accelerated in a process independent of external monitoring techniques that prevents adhesive overheating. In order to design this practitioner-friendly and controllable manufacturing process, kinetic models were developed, allowing the prediction of the degree of cure, α, in dependency of CP content. The kinetic models were applied to experimentally determined temperature profiles during inductive heating of large-scale GiR specimens, considering three commercially available 2 K-EPX, and one 2 K-PUR, all of which are widely used. The kinetic modelling allowed for a much better interpretation of the heating behaviour, highlighting, in particular, the contribution of enthalpy for adhesive curing, and by extension of the whole induction process.

摘要

胶合杆（GiR）如今已广泛确立为木材工程中的粘合连接类型。组件由钢制的杆（例如，螺纹杆或钢筋）或纤维增强的聚合物（FRP）组成，它们被粘合到木质建筑构件中。与机械紧固相反，粘合剂粘结通常会导致被粘物之间更好的载荷传递，因此与机械紧固件相比，可以减小局部应力峰值。GiR的键合通常使用2 K聚氨酯（2 K-PUR）或2 K环氧树脂（2 K-EPX）进行，完全固化可能需要几天的时间。因此，在对连接施加压力或移动连接以进行进一步处理之前，必须将组件保持在固定位置。对于承包商而言，此过程可能非常耗时且成本高昂。为了创建更快，因此更有效的键合过程，本研究借助感应加热的居里粒子（CP）研究了大规模GiR标本的加速固化。CP被添加到粘合剂中，并暴露于高频（HF）电磁场（EMF）中。EMF将混合物加热到居里温度（Ť _ç达到），此时加热会自动停止。由于产生的热量，聚合过程在独立于防止粘合剂过热的外部监控技术的过程中得到了显着加速。为了设计这种对从业者友好且可控制的制造过程，开发了动力学模型，可以根据CP含量预测固化程度α。考虑到广泛使用的三种市售2 K-EPX和一种2 K-PUR，将动力学模型应用于大规模GiR样品感应加热期间实验确定的温度曲线。动力学模型可以更好地解释加热行为，特别是突出了焓对粘合剂固化的贡献，