FE Modeling

On the basis of the results described in the section “Determination of Mechanical Values of the Adhesives," non-linear FE calculations of the push-out tests were performed. One of the project’s aims was the choice of adequate material laws to describe the structural adhesive behavior of the connection of characteristic tests on standardized specimens for each of the adhesive systems (epoxy resin, polyur­ethane, silicone). Both hyper-elastic material laws on the basis of elastic potential (Mooney-Rivlin, Yeoh, Ogden) and a micro-mechanical chain model according to Arruda-Boyce were used; in general these are able to characterize the rubber-like behavior of soft adhesives adequately. For elastic-plastic adhesives it becomes apparent according to Fig. 9 that FE calculations on the basis of von-Mises

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FE Modeling

FIG. 9—Approach for determination of failure criteria based on mechanical values from simple basic tests.

equivalent stresses cannot provide sufficient results for the flow behavior of adhe­sives, especially under tension loading. An improved approximation for building purposes can be achieved with a linear or exponential Drucker-Prager or Mohr – Coulomb relationship. A comparatively new approach according to Schlimmer and Mahnken [22] has not been applied here due to the complex determination of input parameters by characteristic tests, its focus on crash simulation, and the missing implementation in commercial FE software.

As for the analytical method, the FE calculation of component tests using linear modeling of the adhesive behavior describes the test results very well. Here plastic calculations are not expedient at this time because as a first approach the plastic limit shall be far from being reached due to safety reasons. So for typical applications of hybrid beams, analytical models and dimension­ing tables [5] based on linear calculations now are available that can replace complex FE calculations. Thus pilot projects or first applications of such hybrid steel-glass beams for building purposes can be both simplified and accelerated.