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Publication Access status: Open Access , On the Response of Additively Manufactured Micro-Structured Materials to Static and Dynamic Loading(2026-07-20)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.Source Type:Doctoral ThesisSeries:Schriftenreihe des Lehrstuhls für Festkörpermechanik der Universität SiegenVolume number:76 14 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Experimental and numerical investigation on dynamic behavior of soft materials with emphasis on tissue simulant materials(2022)Aghayan, SamInvestigation on the dynamic behavior of soft materials from different kinds of resins to soft biological tissue simulants has became drastically important, due to their vast applications in different sections of industry and material science, particularly in biomedical applications. Such materials have been increasingly used recently for specific-designed biomedical purposes in areas like tissue simulant materials (collagen and agarose). One of the crucial aspect of investigation on these strain-rate dependent materials is related to the impact-induced behavior. Each of these materials could illustrates different behavior when imposed to high-rate loading condition. In this thesis, two groups of soft materials are studied through experimental and numerical approaches. The investigation initiates with soft 3D printing resins known as standard and tough resins, and will continue as the main course of research on very soft tissue simulant material, known as agarose gel, with the focus on brain tissue simulant agarose. In both cases, the behavior of materials in impact-induced condition is investigated. Two types of resins, namely a MMA-based resin and an ABS-based tough resin, are subjected to compression tests on a Split Hopkinson pressure bar to deduce their dynamic properties under high strain rate loading. Two Hopkinson bar setups are used, the first one is equipped with aluminum bars and the second one with PMMA bars. From the measured strain waves, dynamic elastic moduli at high strain rates are derived. The majority of this dissertation presents the experimental and numerical investigations on the dynamic behavior of impact-induced cavitation in agarose gels. The drop tower test was used for the experiments, and agarose samples with three different concentrations similar to soft brain tissue were tested. The acceleration causing the bubble cavitation and the correlated bubble sizes were determined. Such quantitative measurements can be utilized to evaluate brain tissue injuries. In parallel, we present nite element simulations of the drop tower experiment. We model the complete test setup to validate the measurements and derive the relevant pressure fields with simplified models. The numerical solutions are shown to be in excellent agreement with the experimental results of bubble cavitation, enabling substantial simplifications in further investigations of soft tissue under dynamic loading. In addition, to track the volume and pressure variation of the acceleration-induced bubbles after impact, the "Fluid-filled cavity" method is applied in the finite element model, which corresponds well to the experimental outcomes. Our study gives insight into the mechanisms of bubble cavitation in soft tissue. Combined with the numerical simulation, it estimates how impact and pressure waves act and, for example, which areas of the head may be affected by cavitation that induces brain injuries.Source Type:Doctoral ThesisSeries:Schriftenreihe des Lehrstuhls für Festkörpermechanik der Universität SiegenVolume number:62 8 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Flexible Materialien für die additive Fertigung: hyperelastische, viskoelastische Eigenschaften und der Einfluss unsicherer Materialparameter(2019)Additive manufacturing, commonly called 3D printing, has become an established method in many fields of production. It is a preferred method to produce small series or individual parts of components. If such printed parts shall replace traditionally produced parts, the mechanical properties have to be at least comparable. Even enhanced properties are desirable. This works addresses the hyperelastic and viscoelastic properties of different flexible materials in additive manufacturing. Additional an investigation of the influence of material uncertainties, e.g. by voids, is presented. In particular two different printing methods are examined: on the one hand fused deposition modeling (FDM) and on the other hand stereolithography (SLA). While FDM technique uses a meltable plastic as the basic material, the SLA method is based on the hardening of a photopolymeric resin material. To investigate the hyperelastic material properties, uniaxial tensile tests are performed until rupture. For the used specimens, different printing parameters are varied. Uniaxial stress relaxation tests serve to determine the viscoelastic properties. Parameters of different hyper- and viscoelastic material models are identified by a conditional nonlinear regression. The gained parameters are verified in a FEM-simulation. In conclusion the influence of uncertain parameters on different material properties is investigated. One the one hand the size distribution of spherical voids in closed-cell materials is determined, followed by a statistical analysis of the void radii distribution. On the other hand the influence of uncertain material parameters on an output parameter is studied on the example of an Euler-Bernoulli-beam.Source Type:Doctoral ThesisSeries:Schriftenreihe des Lehrstuhls für Festkörpermechanik der Universität SiegenVolume number:23 11
