Thermo-hygro-mechanical characterization and continuum-mechanical modeling of fast curing polyurethane adhesives

在工业中，聚氨酯胶粘剂是常用的胶粘剂。它们在室温下表现出弹性行为，并能容忍大的变形。除了湿固化的单组分体系外，还可以找到双组分的聚氨酯。前一种胶粘剂通常会被混合水分增强，因此也是双组分胶粘剂。在湿固化系统中，端异氰酸酯的预聚体与水(来自环境或助推剂)在氨基甲酸上反应，并将二氧化碳消除为胺，胺与其他异氰酸酯基团反应形成尿素基团。没有湿固化的2K体系通常由树脂组分中的多元醇混合物和固化剂组分中的液体异氰酸酯端基预聚体组成。纯湿基体系的交联是由扩散控制的；固化过程从粘结物表面到主体进行，固化速度随着时间的推移而降低，特别是在形成交联聚合物的皮肤之后。由于引入了助推器，在整个粘合剂体系中混合完各组分后，反应开始，类似于所有2K系统。然后，必须完成与粘接相关的所有技术操作的工作寿命开始。交联剂的使用寿命取决于温度，因此可以通过温度控制来控制固化过程。在行业中，提高固化过程的速度是相当有兴趣的。由于工作寿命的缩短和温度升高导致的加速，连接过程必须在很短的时间内完成，这可能会在要连接的零件的定位过程中造成问题。在长时间打开(对于湿固化1K系统，在皮肤形成之前)或长时间的罐装(2K系统)之后，只有在定位组件以通过定向热输入来提高反应速率之后，才是理想的。可以在极短的时间内将待连接的金属部件加热到所需的温度。在键界面处，升温速率可达到100K/min~100K/min。这种方法被称为快速固化。由于胶粘剂的导热性能较差，在厚度约为5 mm的胶粘剂层中形成了温度梯度。该项目的目标是对快速固化的聚氨酯胶粘剂进行实验表征和连续介质力学模型，以优化固化过程。为此，考虑了所有相关的时间相关性和不均质性。必须开发新的实验技术和材料模型，以表示在水分和热量影响下的交联效应。模型的验证是在模型的基础上进行的，该模型必须被实施到有限元程序中。给出了拉剪试件的试验研究和与实践相关的材料设计。

In the industry, polyurethane adhesives are frequently used. They exhibit elastic behaviour at room temperature and can tolerate large deformations. In addition to moisture-curing one-component systems, two-component polyurethanes can also be found. The former ones are often boosted with blended moisture and, thus, are also two-component adhesives. In moisture-curing systems, an isocyanate-terminated prepolymer reacts with water (from the environment or from the booster) over the carbamic acid and the elimination of carbon dioxide to amine, which reacts with other isocyanate groups to form urea groups. 2K systems without moisture-cure often consist of polyol mixtures in the resin component and a liquid isocyanate-terminated prepolymer in the hardener component. The cross-linking of pure moisture-based systems is controlled by diffusion; the curing takes place from the surface of the bond to the bulk and the rate of cure decreases with time, especially after the formation of a skin of cross-linked polymer. Due to the introduction of boosters the reaction starts, similar to all 2K systems, after mixing of the components throughout the entire adhesive bulk. Then, the working life in which all technical operations related to the bonding must be done begins. Crosslinking and thus the working life depend on the temperature such that the curing can be controlled via temperature control. In the industry, there is considerable interest to increase the speed of curing processes. By the reduced working life and the acceleration which is caused by increasing the temperature, the joining process must be completed in a very short time which can cause problems during the positioning of the parts to be joined. It is desired, after a long open time (for moisture-curing 1K systems, before the formation of the skin) or a long pot life (2K systems), only after positioning of the components to increase the reaction rate by targeted heat input. It is possible to heat the metallic parts to be joined inductively in very short times to the required temperature. At the boundaries of the bond, heating rates between 100 K/min and 100 K/min can be reached. This approach is referred to as rapid curing. Due to the poor thermal conductivity of the adhesives, temperature gradients develop in the adhesive layers which are about 5 mm in thickness.The goal of the project is both the experimental characterization and the continuum mechanical modelling of rapidly curable polyurethane adhesives to optimize curing processes. To this end, all relevant time dependences and inhomogeneities are taken into account. New experimental techniques and material models must be developed that can represent cross-linking effects under the influence of both moisture and heat. The validation of the model is performed on the basis of the model which has to be implemented into a finite element program. Experimental tests uning tensile-shear specimen and practice-relevant material design are providewd.