ABSTRACT

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 (T_c) 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 T_Cure(t) and the CP content c_cp. 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.

摘要

在粘合剂粘合技术的背景下，加速粘合剂的聚合一直是一个历史悠久的研究领域，因为与大多数机械连接技术（如铆接或螺钉连接）相比，较长的固化时间（有时长达数天）是一个决定性的劣势。除了例如通过UV、微波或IR辐射固化之外，电磁感应代表了一种用于加速聚合物固化的有希望的解决方案。使用这种方法，粘合的组件会受到交变电磁场 (EMF) 的影响，该电磁场会在 EMF 敏感材料中产生热量，例如.，钢或铝。如果没有给出待粘合材料的固有 EMF 敏感性，则将不同类型的感受器（如网、纤维或颗粒）添加到粘合剂中，以便感应加热，从而从内部固化粘合剂。最近的研究集中在一种特殊类型的感受器上，即所谓的居里粒子 (CP)，它只能通过感应方式加热到其特定的居里温度 ( T _c) CP 引起的加热自动停止。因此，创建了一种固化过程，无需外部温度监测，同时防止粘合过热。由于潜在的固化动力学——最重要的是聚合焓和固化时间——根据所考虑的粘合剂而有显着差异，实现完全固化所需的诱导时间目前必须通过在实验水平上进行昂贵的初步调查来确定。因此，为了促进更有效和可控的粘合过程，本研究旨在开发一种基于有限元方法 (FEM) 的数值模型，该模型能够根据_固化温度曲线T Cure (t ) 和 CP 含量c _cp。为此，将两种根本不同的 2K 环氧树脂粘合剂的固化动力学与基于实验确定的热负荷的瞬态热流模拟相关联。使用感应固化的大型胶合棒 (GiR) 试样的示例应用成功地验证了开发的 FEA 技术，由此实验确定的温度曲线与数值预测非常吻合。本文重点介绍了初步的实验工作以及为数值建模实施的所有分析方法。