Bieler, Sören

When a vehicle leaves the road, crash barriers stop it and prevent significant damage to the vehicle, its environment, and the occupants. Typically, such protection systems are made of simple steel, but fiber-reinforced composites can efficiently absorb and dissipate the impact energy at high-risk locations. In order to design such protective systems, material parameters under dynamic loading are necessary. Here, split Hopkinson pressure bar tests with unidirectional glass-fiber-reinforced epoxy of 58% glass fiber content are performed. The elastic response at strain rates between 300/s and 700/s in the loading direction parallel and perpendicular to the fiber is determined. From the measured data, a model of the time dependence of the elastic modulus is derived to enable the design engineer to lay out protective systems made of such GFRPs.

The study of material behavior is a fundamental aspect of research in science and engineering, as it directly influences the design, performance, and reliability of components across a wide range of applications. For most applications, static tests are performed by relevant standards to determine material data. Since technical constructions like buildings, bridges etc. are considered not to move with time, quasi-static materials parameter are sufficiant to calculate stability of such construction. Under varying loading conditions, especially under dynamic or high-strain-rate impacts, materials can exhibit significantly different mechanical responses compared to those observed under quasi-static conditions. This discrepancy poses challenges for accurate modeling and prediction of material performance in some scenarios, such as in automotive crashes, ballistic impacts, or aerospace applications. As a result, a deeper understanding of the mechanical behavior of materials under dynamic loading is essential for developing more robust and efficient structures. In this context, experimental methods and numerical simulations play a critical role in characterizing and predicting material response under such extreme conditions. The split Hopkinson pressure bar test is a key experimental device in determining material behavior under high strain rates. Additive manufacturing has developed steadily over the years and is now used not only for prototyping but also in series production. There are nearly no limits to the complexity of structures and components that can be achieved with additive manufacturing, as it allows for structures that would be difficult or impossible to achieve with conventional manufacturing processes. In this work, different additive manufactured materials are examined in terms of their behavior under static and dynamic loading. Energy absorption plays an important role, particularly in the case of impact forces acting on the body. Materials that enable good energy absorption through deformation are particularly suitable for this purpose. Lattice structures can exhibit damping properties with relatively low material costs, which, with the appropriate choice of materials, are also designed for multiple loads and thus represent sustainable energy-absorbing structures. Therefore, this study examines 3D-printed structures made of a TPU-like material subjected to multiple impact loads. The same types of structures are used to examine their energy-absorbing properties under quasi-static loads, but in this scenario, by structures made of hard, acrylic-like materials. For both types of loading, eight structural types are compared for their specific energy absorption properties. Various structural parameters are considered, including the number of struts or the structure's surface areas. By designing the individual structure types in this way, the same relative densities can be achieved across all structures, enabling a fair comparison. This work aims to determine the significant differences between static and dynamic loads for additively manufactured specimens made of different materials. Based on the results obtained, initial simulations for such test conditions can be created and compared with the experiments. Furthermore, the experiments are intended to investigate and compare the energy absorption behavior of different structures with the same relative density.

This paper aims to investigate multiple large-strain topology-optimized structures, by interpreting their overlay as a probability density function. Such a strategy is suited to finding an optimum design of silicon electrodes subject to a random contact. Using this method, and prescribing a zero net-force constraint on the global system, the optimum structure is identified with a Schwarz P minimum-surface structure. Then, the optimum structure is subject to chemo-mechanically coupled cycling, in terms of an irreversible thermodynamic process, which shows the interplay between the mechanical and chemical fields. The Matlab-based optimization code is attached.

Bieler, Sören

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