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Cohesive zone model for moist adhesive joints

: Hesebeck, Olaf; Goldschmidt, Florian; Diebels, Stefan


Possart, Wulff; Brede, Markus:
Adhesive joints. Ageing and durability of epoxies and polyurethanes
Weinheim: Wiley-VCH, 2019
ISBN: 978-3-527-34185-6 (Print)
ISBN: 978-3-527-80375-0
ISBN: 978-3-527-80377-4
ISBN: 978-3-527-80374-3
Bundesministerium fur Wirtschaft und Energie BMWi (Deutschland)
IGF; 17276 N; FOSTA
Bruchverhalten von Klebverbindungen und Kohäsivzonenmodell - Einfluss der Herstellung und Alterung
Book Article
Fraunhofer IFAM ()

Chapter B.6 discussed the extension of visco‐elastic adhesive models to account for different spatially varying influence factors, for example the local concentration of water in the adhesive. While this kind of extension offers the potential to improve the modelling, it seems to imply a large increase of effort in the simulation of the behaviour of an adhesive joint in an industrial application. Therefore, a simplified approach offering the main advantages of the model extension at a low cost is desirable for an industrial application in the near future.
This topic is addressed in Chapter B.8. In particular, we will show how the viscoelastic model considering the influence of diffusing water and of temperature can be applied at a reasonable computational cost and modelling effort. Furthermore, the step will be made from an implementation in scientific finite element software to a realization in a commercially available finite element program.
One important step in the reduction of effort is the transfer of the three‐dimensional adhesive material model to a cohesive zone model of the adhesive layer. Due to the low computational cost, cohesive zone models have become popular in the recent years. For example, the use of cohesive zone models to consider adhesive joints in automotive crash simulation is state of technology today.
Next, the coupling between the water diffusion and the mechanical behaviour of the adhesive joint needs to be considered. If the response to a short‐term load after a long‐term exposure to water should be simulated, a consecutive diffusion and stress‐strain analysis are sufficient. We employ closed form solutions and finite element analysis as alternative methods to calculate the diffusion.
Once the spatial distribution of water concentration in the adhesive is determined, the mechanical material properties can be calculated for any point within the adhesive layer according to the model presented in chapter B.6. For a finite element analysis this means that each adhesive element has to be assigned its individual set of material properties. A manual assignment of these properties by the engineer creating the FE model requires an effort which would prohibit the employment of the extended models in industrial applications. In order to keep the modelling effort within limits acceptable in industrial application, this assignment must not be performed manually but automation is required. The feasibility of such an automation is shown by the development and test of an automation script for the specific case of rectangular adhesive layers.