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Strain rate dependent characterizations of glass fiber reinforced thermoplastic (LFT) under different multiaxialities show an increasing fracture strain and higher energy absorption capacity if the loading rate rises. The present paper gives a clue for the underlying micro-thermo-mechanical mechanisms of this effect. The method of correlating experimental field information of strain and heat generation provides data for advanced analysis. Strain and heat distribution of the deformation zone as well as a hot-spot occurrence display give hints on expanded damage zones at high strain rates. Quasi-static and dynamic interrupted tensile tests provided data to investigate the damage evolution. Scanning electron microscopic (SEM) images show differences in the area between fiber and matrix depending on the strain rate. Based on SEM images and correlated and analyzed field data a model representation was established that presents, in agreement with the literature, a perception of the damage mechanisms in the interface and its consequences for global deformation.
Dehnratenabhängige Charakterisierungen von langglasfaserverstärkten Thermoplasten (LFT) unter verschiedenen Mehrachsigkeiten zeigen eine zunehmende Bruchdehnung und eine höhere Energieabsorptionsfähigkeit, wenn die Prüfgeschwindigkeit ansteigt. Die Ergebnisse dieser Arbeit geben einen Hinweis auf die zugrundeliegenden mikro-thermomechanischen Mechanismen dieses Effekts. Die Methode der Feldkorrelation, bei der experimentelle Felddaten der Verformung und der Temperaturentwicklung zusammengeführt werden, liefert die Basis für Untersuchung der dehnratenabhängigen Schädigungsentwicklung. Verformungen aus der Grauwertkorrelationsanalyse und Wärmefelder aus schnellen Infrarotmessungen führen bei einer Kombination der Daten zu der Erkenntnis, dass die Deformationszone sich ausbreitet und die Anza hl von lokalen Temperaturerhöhungen (Hotspots) mit steigender Dehnrate zunimmt.
Thermo-mechanical material considerations have been published since two centuries. A new method of correlating experimental field information of strain and heat generate data for a physical based thermo-mechanical modeling of strain rate dependent material properties. Strain rate dependent characterizations under tensile loading of glass-fiber reinforced thermoplastic (LFRT) and its matrix material polypropylene (PP) were conducted. Higher fracture strains of LFRT with raising strain rate could be ascertained in contrast to the decreasing fracture strain of PP. High-speed video based digital image correlation (DIC) in combination with high-speed infra-red (IR) measurements provide field data of the deformation and the temperature evolution. A precise IR calibration method, the correlation of the Lagrangian deformation field with the Eulerian temperature field, the contemplation of volume specific values and the incorporation of the thermo-elasticity allowed the determination of the heat transition values with respect to strain and strain rate. The results show clear difference of (βdiff) between PP and LFRT. While PP shows a higher βdiff with rising strain rate and therefore higher energy dissipation, βdiff of LFRT decreases with the strain rate. The predominant role of thermo-elasticity was identified as the key-factor of higher energy absorption of LFRT at higher strain rates.
The dynamic material characterization shows different macroscopic strain rate effects. The causal mechanisms cannot be identified at this level in most cases. Micro-tests allow a local transient analysis, which is illustrated in this article using the example of a long-fibre reinforced thermoplastic (LFRT). After a general introduction, the development and validation of a micro-test for a large strain rate range is presented. The validation explained for steel shows the advantage of the small sample for the dynamic characterization, if a homogenous material behaviour of this magnitude still exists, especially in the case of low-vibration force measurement. For a heterogeneous LFRT material, the micro-test shows strongly scattering test results that are no longer representative of the homogenized mechanical material behaviour, but reflect the local characteristics. These local properties are directly caused by the injection moulding process. Further SEM analyses of the samples indicate different macromolecular deformation mechanisms of the matrix at the different strain rates.
Long-fiber reinforced thermoplastics (LFT) were characterized for automotive applications with high rate experiments in a range of strain rate from 10⁻³s⁻¹ up to 10²s⁻¹. High-speed video imaging with digital image correlation (DIC) and a high-speed infra-red camera are applied to investigate the strain and temperature development during four different testing types. Different states of stress were investigated to provide adequate input data for simulation. A new fracture initiation criterion is introduced. Nearly pure shear load could be reached with a specifically designed specimen. It was found that global deformations rise with the strain rate, while local strains decrease. The adiabatic temperature-rise enlarges the deformation zone, impedes strain localization and leads to higher energy absorption at higher strain rates.
In dieser Arbeit wurde eine Methode entwickelt, um Informationen über Defektverteilungen aus CT-Analysen von Gussbauteilen (AlSiMg,EN-AC- 43000) auf ein Finite-Elemente-Modell (FE) zu übertragen. Da die Daten einer CT-Analyse sehr groß sind, war eine Datenreduktion erforderlich. Dies erfolgte durch die am Fraunhofer IWM entwickelte Software MaterialDatatFusion MDF, bei dem die Porenverteilung vereinfacht wird. Die Porenverteilungen wurden untersucht und auf die FE-Modelle gemappt. Daneben wurde ein Deformations- und Versagensmodell für den Aluminiumguss mit Einfluss des Defektanteils kalibriert. Damit und mit der elementweisen ermittelten Verteilung der Porosität wurden Probenversuche simuliert, die aus realen Gussbauteilen entnommen wurden. Für die exakte Probenentnahme diente MDF der genauen Zuordnung der Porosität im Prüfbereich. Die simulierten Kraft-Verschiebungskurven sowie die ermittelte Porosität wurden mit der realen Verteilung der Poren und den Experimenten verglichen.
Most electric scooter-related injuries occur in single crashes, and the reported use of helmets during these accidents is very low. The objective of this study is to numerically investigate single e-scooter accidents at kerbs. A finite element (FE) model containing the THUMS AM50 V4.02, an e-scooter, a helmet, and a rigid kerbstone was created. The FE helmet model was parameterised by material characterisation and standard helmet tests, and a new, unconventional helmet testing setup was proposed. In a parametric study using the FE solver LS-DYNA, collisions of the e-scooter rider against the kerb with three different velocities (10, 20, 30 km/h), two different impact angles (90°, 60°), and with and without the helmet were investigated. The accelerations at the head’s centre of gravity were measured, and the injury criteria HIC, BrIC, and CSDM were evaluated. The variation of the collision angle influenced the body kinematics and the injury criteria values. Higher e-scooter collision speeds resulted in higher impact speeds and increased HIC. The wearing of a helmet was the main factor in the reduction of translational impact accelerations and HIC, while for BrIC and CSDM, whether the values increased or decreased depended on the collision scenario.
Preprint: Optimizing Computational Efficiency in TPMS Structural Design through Surrogate Modeling
(2025)
This paper introduces a surrogate modeling approach for simulating Triply Periodic Minimal Surfaces (TPMS), which can be used in various engineering applications due to their unique geometric, mechanical properties and light weight properties as a second hierarchy level below the component design level. The detailed finite element analysis of theses structure in components, require inten- sive computational resources due to the complex geometries of TPMS. To address these challenges, we propose a surrogate model that simplifies the geometric and mechanical representation of TPMS, enabling more effcient simulations without compromising accuracy. This model was validated against experimental data from bending tests performed on TPMS structures fabricated using additive manufac- turing techniques. The surrogate model demonstrated excellent agreement with experimental results, offering a promising tool for the rapid and effcient design of TPMS-based components. The model’s utility is underscored by its application in predicting the mechanical behavior of TPMS structures under various loading conditions, confirming its potential for broader adoption in engineering design processes.
Die dynamische Werkstoffcharakterisierung für die Crashsimulation wurde in den vergangenen 20 Jahren auf alle Bereiche im Fahrzeug ausgedehnt, einschließlich der Lithium-Ionen Akkus in den Batteriepacks. Nachdem in den vorhergehenden Jahren der Fokus auf den Stahlstrukturen lag, werden heute alle Materialgruppen, Materialverbünde und auch Verbindungen betrachtet. Damit hat sich auch das Spektrum der Werkstoffcharakterisierung deutlich erweitert. Ein Meilenstein dabei ist sicher die Nutzung von lokaler Dehnungsanalyse mit Hilfe der Grauwertkorrelation und leistungsfähiger digitaler Hochgeschwindigkeitsvideokameras. Die Grauwertkorrelation erlaubte erstmals eine variable flächige Analyse der transienten Dehnungen auf ebenen und später auch auf gekrümmten Oberflächen. Das konnten Dehnungsmessstreifen (DMS) oder Extensometer nicht leisten. Außerdem werden flächige experimentelle Daten als Referenz zur Verifizierung der Simulationsergebnisse bereitgestellt. Ausgehend von dieser Thematik werden in diesem Beitrag einige Entwicklungen in der dynamischen Werkstoffcharakterisierung für Crash- und Impaktsimulationen dargestellt.