Size effects in bonds : experiments and modelling

Klebstoffe haben heutzutage eine große Bedeutung in wichtigen Wirtschaftsbranchen, wie z. B. im Automobilbau, im Schienenfahrzeugbau, in der Luft- und Raumfahrttechnik, im Maschinenbau und in der Elektrotechnik/ Elektronik, so dass ein großes Interesse daran besteht, das mechanische Verhalten geklebter Werkstoffe durch geeignete Modelle zu erfassen und über Simulationen Voraussagen in Bezug auf den Einsatzbereich und die Einsatzfähigkeit treffen zu können. In der vorliegenden Arbeit geht es um die Modellierung von Klebungen aus Polyurethan. Diese Klebungen zeigen, je nach Schichtdicke, ein unterschiedliches mechanisches Verhalten unter Belastung. Dieses mechanische Verhalten wird in entsprechenden Experimenten (Schub- und Zugversuche) charakterisiert. Auf der theoretischen Seite wird ein auf den experimentellen Datenpool gestütztes, erweitertes kontinuumsmechanisches Materialmodell entwickelt und numerisch umgesetzt. Die eingeführten Material- und Modellparameter werden über die Parameteridentifikation anhand der experimentellen Daten bestimmt. Zum Abschluss wird die Tauglichkeit des Modells durch eine zusätzliche Anwendungsmöglichkeit im Bereich gefüllter Polymere demonstriert.Adhesives are widely used in many important branches of industrial applications, i. e. in automotive, aeronautical, electrical and mechanical engineering. Thus, it is of major importance to describe the mechanical behaviour of such adhesive joints appropriately in order to prognosticate their behaviour with respect to the application area and the utilisability. The present work deals with the modelling of polyurethane bonds. These bonds show a significantly different mechanical behaviour depending on their thickness. Experimental investigations (shear and uniaxial tension tests) are performed to characterise the mechanical properties. On the theoretical side, an extended continuum mechanical model which is based on the experimental data is developed and numerically implemented. The introduced material and model parameters are determined via the parameter identification according to the experimental data. Concluding, the model\u27;s efficiency is demonstrated by presenting further possible applications in the range of filled polymers

Viscoelastic behavior of filled silicone elastomers and influence of aging in inert and hermetic environment

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Effective properties and size effects in filled polymers

Filled polymers are of special interest according to their superior mechanical properties. Special attention is given to nano-filled polymers where not only the volume fraction but also the internal surface has a significant contribution to the effective properties. In the present contribution the increase in stiffness with decreasing size of the fillers at constant volume fraction of the fillers is modelled by a phenomenological, i.e. continuum-based, approach taking into account large deformations. The proposed multiphase model allows for a systematic investigation of increasing surface-to-volume ratio which becomes important for micro- and nanosized fillers. The numerical treatment of the proposed model is based on a coupled Galerkin finite element formulation

The study of fatigue behavior of thermally aged rubber based on natural rubber and butadiene rubber

This work is focused on investigation of the influence of thermal aging on fatigue behavior of carbon black filled rubber compounds which have been based on Natural Rubber (NR), Butadiene Rubber (BR) and their blend with ratio 50/50. The thermal aging was performed in thermal chamber at varied temperatures 30, 70 and 110°C for 720 hours. Firstly, the influence of thermal aging on mechanical behavior under quasi-static tensile test followed by Dynamic Mechanical Analysis (DMA) has been investigated. The fatigue behavior under sinusoidal waveform loading conditions has quantitatively been analyzed by using of dynamic testing equipment Tear and Fatigue Analyzer. The aim of this work was to investigate the influence of thermal aging on the fatigue behavior of rubber based on varied rubber types to understand the relationship between the thermal degradative processes occurred in rubber matrix under thermal aging and fatigue life. From the experimental work it was concluded based on all used testing methods, that the presence of BR rubber enhances the resistance against thermal aging and thus could be used as an efficient component reducing the aging degradation in rubber blend systems. © 2017 Taylor & Francis Group, London, UK.Operational Program Research and Development for Innovations; European Regional Development Fund (ERDF)European Union (EU); national budget of the Czech Republic, within the framework of the project CPS-strengthening research capacity [CZ.1.05/2.1.00/19.0409]; Ministry of Education, Youth and Sports of the Czech Republic-Program NPU I [LO1504]; Bavarian State Ministry of Education, Science and the Arts; Ministry of Education, Youth and Sports of the Czech RepublicMinistry of Education, Youth & Sports - Czech Republic [8E15B007

Thermal analysis and shrinkage characterization of the photopolymers for DLP additive manufacturing processes

International audienceThis paper proposes an experimental investigation of a commercial photopolymer resin followed by material modelling and manufacturing system characterization. We focus on the effect of the degree of cure and temperature on the material properties of the photopolymer materials. UV curing properties of the liquid resin are assessed with the thickness measurement by optical tomography. Besides, the specific heat capacity is determined for the almost completely cured and uncured samples with DSC measurements. Photo-DSC experiments are performed to investigate the curing reaction and modelling of the evolution of the degree of cure depending on the light intensity and temperature. In addition, chemical shrinkage behaviour is captured as function of the degree of cure by the high-precision balance setup. As a result of our experimental studies, model equations are proposed to describe the material behaviour

Curing-dependent thermo-viscoelastic and shrinkage behaviour of photopolymers

International audienceThis study investigates the influence of curing on the thermo-viscoelastic properties and chemical shrinkage of a commercially available photopolymer resin used in SLA and DLP 3D printing and presents a modelling approach for predicting material properties. UV rheometer and DMA measurements were performed to investigate the viscoelastic properties of the photopolymer material as a function of temperature, degree of cure, and frequency. Time–temperature and time-cure superposition principles were applied to the experimental results. In addition, the chemical shrinkage behaviour was studied by the UV rheometer as a function of the degree of cure and temperature, and a model equation was proposed based on these parameters. Our experimental findings have led to the development of constitutive equations for the complete material behaviour

Advanced Characterisation of Soft Polymers under Cyclic Loading in Context of Engine Mounts

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

A thermo-coupled constitutive model for semi-crystalline polymers at finite strains: Application across scales

Fiber reinforced thermoplastics are widely used for thermoforming and injection moulding processes, since their high strength to mass ratio is favorable for various industrial applications such as, for example, automotive engineering. Semi-crystalline polymers, as the composites matrix material, make up a subcategory of thermoplastics, which partly crystallize after cool-down from the molten state. They are reinforced with glass or carbon fibers to enhance their material performance. Nevertheless,during the thermoforming process, unwanted residual stresses can arise, due to the complex material behavior of semi-crystalline polymers under different temperatures and strain rates. The interaction between matrix and reinforcement being another unknown factor. Therefore, computational models are needed to predict the material response reliably and minimize production errors.This work presents a thermomechanically consistent phenomenological material formulation for thermoplastics at finite strains.In order to account for the highly nonlinear material behavior, elasto-plastic and visco-elastic contributions are combined in the model formulation. To account for the crystalline regions, a hyperelastic-plastic framework is chosen and extended with a tension-compression asymmetry in yielding. The material parameters, characterized using experimental results, depend on both,the temperature as well as the degree of crystallinity. Together with a linear elastic material model for glass fibers, the matrix formulation is embedded in a representative volume element with unidirectional fiber reinforcement to demonstrate the capabilities of the modeling framework in a multiscale context. A comparison of the virtual testing at varying temperatures and degrees ofcrystallinities to experimentally obtained results is planned as future work

Future-Oriented Experimental Characterization of 3D Printed and Conventional Elastomers Based on Their Swelling Behavior

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