The present study investigates different elastomers with regard to their behavior towards liquids such as moisture, fuels, or fuel components. First, four additively manufactured materials are examined in detail with respect to their swelling in the fuel component toluene as well as in water. The chemical nature of the materials is elucidated by means of infrared spectroscopy. The experimentally derived absorption curves of the materials in the liquids are described mathematically using Fick’s diffusion law. The mechanical behavior is determined by uniaxial tensile tests, which are evaluated on the basis of stress and strain at break. The results of the study allow for deriving valuable recommendations regarding the printing process and postprocessing. Second, this article investigates the swelling behavior of new as well as thermo-oxidatively aged elastomers in synthetic fuels. For this purpose, an analysis routine is presented using sorption experiments combined with gas chromatography and mass spectrometry and is thus capable of analyzing the swelling behavior multifacetted. The transition of elastomer constituents into the surrounding fuel at different aging and sorption times is determined precisely. The change in mechanical properties is quantified using density measurements, micro Shore A hardness measurements, and the parameters stress and strain at break from uniaxial tensile tests.
Many industrial applications require natural rubber (NR) as an irreplaceable polymer for its unique behaviour as its resistance to crack growth. The damage caused by ozone, seen as an ageing accelerator, influences the lifetime of rubber components. The data on ozone-induced ageing experiments are often incomplete or remain unpublished, whereas comprehensive databases for other environmental loads as oxygen do exist. A variety of experimental methods is used to investigate the ageing mechanism of ozone. The ultimate scope is to collect physically based data suitable to include it in thermo-mechanical modelling of the material’s full behaviour. Therefore, NR mixtures, without and with antiozonants: p-phenylenediamine (PPD) and paraffinic wax, are analysed. First, an accelerated, artificial ageing method is developed to reconstruct the real ageing in the laboratory. Experiments conducted henceforth are microhardness tests, uniaxial tensile tests and IR spectroscopy to determine the elastic modulus, the stress response and molecular change due to ageing. Independent of static deformation during the ageing process, both antiozonants show a significant protection effect up to the maximum loading with 75 pphm ozone concentration for 111 h at 50% relative humidity and 40 $$^\circ $$ ∘ C. Paraffinic wax completely prevents measureable mechanical change and no surface cracks are visible, though IR spectra reveal ageing-induced molecular reactions, whereas the pristine and soley 6PPD protected compounds are clearly distinguishable by their surface crack picture. Neither of the material compounds, loaded with or without strain during ozone-ageing, contains cracks of a depth further than 300 $$\upmu {\mathrm {m}}$$ μ m . The data generated on ozone ageing of rubber helps to distinguish it from thermo-oxidative ageing that is described comprehensively in the literature. In conclusion, the data proves the degradation and quantifies some characteristic material changes caused by ozone loading.
A thermodynamically consistent concept to model the strain-induced crystallisation phenomenon using a multiphase approach is discussed in Loos et al. (CMAT 32(2):501–526,2020). In this follow-up contribution, the same mechanical framework is used to construct a second model that sets the same three phases in a serial connection, demonstrating an alternative to the former parallel connection of phases. The hybrid free energy is used to derive the constitutive equations. The evaluation of the Clausius–Duhem inequality ensures thermomechanical consistency. The model is based on a one-dimensional derivation that extends with the concept of representative directions to a three-dimensional anisotropic model. After the step-by-step derivation, the performance of the model is analysed in detail, including its comparison to the well-known Flory model, its evaluation for infinite fast and slow excitations, its simulation of uniaxial cycles and its validation via relaxation experiments. Finally, the model is compared comprehensively to the former parallel model showing their equivalent reason for existence.
The experimental investigation of viscoelastic behavior of cyclically loaded elastomeric components with respect to the time and the frequency domain is critical for industrial applications. Moreover, the validation of this behavior through numerical simulations as part of the concept of virtual prototypes is equally important. Experiments, combined measurements and test setups for samples as well as for rubber-metal components are presented and evaluated with regard to their industrial application. For application in electric vehicles with relevant excitation frequencies substantially higher than by conventional drive trains, high-frequency dynamic stiffness measurements are performed up to 3000 Hz on a newly developed test bench for elastomeric samples and components. The new test bench is compared with the standard dynamic measurement method for characterization of soft polymers. A significant difference between the measured dynamic stiffness values, caused by internal resonance of the bushing, is presented. This effect has a direct impact on the acoustic behavior of the vehicle and goes undetected by conventional measurement methods due to their lower frequency range. Furthermore, for application in vehicles with internal combustion engine, where the mechanical excitation amplitudes are significantly larger than by vehicles with electric engines, a new concept for the identification of viscoelastic material parameters that is suitable for the representation of large periodic deformations under consideration of energy dissipation is described. This dissipated energy causes self-heating of the polymer and leads to the precocious aging and failure of the elastomeric component. The validation of this concept is carried out thermally and mechanically on specimen and component level. Using the approaches developed in this work, the behavior of cyclically loaded elastomeric engine mounts in different applications can be simulated to reduce the time spent and save on the costs necessary for the production of prototypes.
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