Magnetic elastomer composites based on SBR and NR have been compounded and characterized in order to observe the potential changes in mechanical properties in the presence of an external magnetic field. Micron-sized carbonyl iron and manganese zinc ferrite particles of a variety of sizes as well as nano-sized particles composed of an iron oxide were used as magnetic fillers. Mechanical and rheological experiments show that the modification of the particle surface by silane increases the hardness and tensile strength of the materials significantly. The composites filled with carbonyl iron exhibit a better controllable elastic modulus than samples filled with manganese zinc ferrite or iron oxide.

In this work an approach is shown how to combine or unify the two classical methods. An important prerequisite for the fracture mechanics calculations is the knowledge of the initial crack or flaw sizes within the elastomer material. High resolution x-ray Computer Tomography (CT) as a non destructive method to characterize the structures inside the material show that the particles size distribution for the highly stressed volume correlates to the lifetime of the samples. Therefore it will be shown that fracture mechanics calculations starting with the flaw size distributions directly lead to (Wohler-) s-n-curves. Furthermore, the probability of early failures and the dependence of the tested volume to the lifetime prediction can be calculated which is of high practical importance. The results of the calculations and of the experimental work on elastomer materials differing in carbon black dispersion will be discussed.

Isotropic magnetorheological elastomers (MREs) were strained in a tear analyser and growth of single edge notches (SENs) were monitored and compared with a conventional elastomer as a reference material. The MREs were found to have a lower rate of crack propagation than the reference material and exhibited higher fatigue resistance. The enhanced performance of the MREs compared with the reference material was attributed to differences in the matrix recipes, which affected the elasticity of the composite materials. However, it was clear that the addition of magnetic particles did not weaken the composite material in the short-term or act as stress raisers from which cracks could propagate and shorten the component life.

This paper presents the results of the research on the fabrication and characterization of barium M-type hexaferrite and its influence on the properties of butadiene-rubber composites. Nanocrystaline barium ferrite particles were prepared by co-precipitation followed by defined mechanical milling in a high energy mill. The particle size, magnetic properties and phase constitution of bulk and milled barium ferrite were investigated by TEM, XRD and Mossbauer spectroscopy. The characterized bulk and milled barium ferrite particles were mixed with the 1.4-cis butadiene rubber and oriented in the presence and absence of the magnetic field and fixed during the vulcanization process. The switchability of the viscoelastic properties of the magnetoactive BR-composites was demonstrated.

This work presents some important remarks on predicting the lifetime of complex rubber parts by taking into account the results from prestrained cycled tension tests and multiaxial tests like simple shear with rotating axis. The experiments are accompanied by finite element simulations, which show the lack of hyperelastic models used for estimating the inhomogeneous stress distribution in cyclic loaded rubber parts.

Common lifetime predictions usually are made with the help of cyclic uniaxial tension tests till failure, whereby the mean value and the amplitude of the load are varied in the course of a test series. However in most rubber-applications, uniaxial tension is not the predominant deformation, so that lifetime predictions, based on equidirectional experiments in those cases inevitably lead to an error. Moreover the deformations in technical rubber products are a mixture of many different loadings which change their direction throughout the deformation process. For the decoupling on laboratory scale of modulated loads and modulated directions a new experimental rig has been developed which enables lifetime investigations under simple shear loads with rotating axes.

The possibility and actual limitations for the analysis of polymer composites in general and in particular of elastomers with a high-resolution x-ray computer tomograph (CT) is presented. The method to reconstruct a 3D volume from a 2D x-ray projection is described in detail to get an idea of the advantages and disadvantages. Furthermore on the basis of some important questions in rubber industries and their solutions, the need of the high-resolution,tomograph and due to new methods of analysis are shown for some selective problems. The investigation of porosity in elastomers, analysis of the microstructure of composites (rubber-metal, fibres-reinforced composites etc.), non-destructive quality control and dispersion analysis are demonstrated.

The encapsulation of solar cells in polymeric sheets such as ethylene-vinyl acetate (EVA) is one crucial step in the fabrication of photovoltaic modules, as it commonly takes several minutes in a heated vacuum chamber. It is therefore a shared goal of PV module manufacturers to reduce the time needed to cure the encapsulant. However, such increased processing speed may result in poor EVA properties, such as a high content of residual aggressive reaction starters. As a consequence the module is highly prone to ageing, in particular delamination, yellowing and corrosion. We present a phenomenological mathematical description of the curing dynamics of a commercially available EVA sheet, which lays the foundation for a systematic search for optimized curing processes. This model is developed from isothermal rheometric measurements of the cure. We find that a model consisting of an initial incubation time followed by two competing reaction paths shows good agreement with the data. A validation is performed by extending the model to non-isothermal conditions and comparing it with experiments.

The possibility and actual limitations for the analysis of polymer composites in general and in particular of elastomers with a high-resolution x-ray computer tomograph (CT) is presented. The method to reconstruct a 3D volume from a 2D x-ray projection is described in detail to get an idea of the advantages and disadvantages. Furthermore on the basis of some important questions in rubber industries and their solutions, the need of the high-resolution tomograph and due to new methods of analysis are shown for some selective problems. The investigation of porosity in elastomers, analysis of the microstructure of composites (rubber-metal, fibres-reinforced composites etc.), non-destructive quality control and dispersion analysis are demonstrated.

Lifetime predictions of technical rubber products in most cases are based on long time fatigue experiments. During those experiments the samples are cyclically loaded till failure. Usually the loading is initiated with an uniaxial deformation whereby the amplitude and the mean value of the load is varied in the course of the test series. However, in the majority of cases the dominant loading condition in rubber-parts is a mixture of many different loading conditions. Moreover, the loading direction in a material point does not remain constant but often changes throughout the deformation process. Therefore, a lifetime prediction with conventional approaches, based on data from equidirectional experiments leads to an error for inelastic and anisotropic materials under the described loading conditions. For the decoupling on the laboratory scale of the dependencies of the lifetime on the loading amplitude on the one hand and on the change of the loading direction on the other hand, an experimental rig according to (Gent 1960) has been developed, which is used in a new way for lifetime investigations under simple shear loads with rotary axes.

The durability of NR-based elastomer material has been examined by stress relaxation and chemical analytical methods in order to investigate the impact of chemical ageing on relaxation processes. The secondary relaxation process, which is derived by separation from the stress relaxation curve, is found to be closely related to the oxidation induction time detected by chemiluminescence. It is suggested that thermal exposition during the initial phase of stress relaxation is mainly due to rearrangement of the filler network and polymer-filler interactions.

The material characteristics of elastomers are determined by the raw material formulation, by manufacturing and cross linking. The durability distribution of dynamically loaded rubber parts is especially determined by the homogeneity of the compound. The smaller the defects in a vulcanisate the longer the final part withstand the dynamic load.

The goal of the work was to prepare magnetic elastomers based on a highly elastic polymer matrix (1,4-cis butadiene rubber) filled with magnetic particles. Barium ferrite (BaFe12O19) powder with a relatively high saturation magnetization and coercivity was synthesized by co-precipitation method and subsequently used as a magnetic filler. The crystal structure, morphology, the particle size and magnetic properties were characterized by XRD, Mossbauer spectroscopy, electron microscopy, and magnetization measurements. During the vulcanization process, ferrimagnetic BaFe12O19 with the shape of hexagonal platelets were oriented in the polymer matrix along the direction of an applied external magnetic field. The changes in physical-mechanical and dynamic-mechanical properties of the ferrite-rubber composites vulcanized in the presence and absence the presence of an external magnetic field were evaluated.

The material characteristics of elastomers are determined by the raw material formulation, by manufacturing and cross linking. The durability distribution of dynamically loaded rubber parts is especially determined by the homogeneity of the compound. The smaller the defects in a vulcanisate the longer the final part withstand the dynamic load.

The dynamic mechanical properties of unfilled and filled solution SBRs, displaying a systematic variation of the vinyl and styrene content, were investigated at high frequencies (0,5 MHz) by means of an ultrasonic spectrometer. The measured sound velocity and damping allowed for the calculation of the complex longitudinal wave modulus. The glass transition temperatures, measured at the peak maximum of the damping factor a at 0.5 MHz, are shifted by 36 to 42 degrees C if compared to the Tg's measured at 1 Hz by dynamic mechanical spectroscopy. The amplitude of the damping signal increases specifically as a function of the vinyl and styrene content. The influence of the filler is predominantely an increase of the amplitude of the damping signal and the longitudinal wave modulus. The filler effect on loss properties is more pronounced for carbon black than for silanized silica for the considered materials.

This research develops a method for assimilating stress softening of elastomers into finite element analysis (FEA) using standard software and phenomenological material models. This required the design and implementation of a user subroutine which can be included in standard code to allow accurate simulation of stress softening effects for elastomeric components or test specimens. Experimental methods corroborated the FEA simulations and hence validated the subroutine allowing its implementation. The method used in conjunction with physical testing was 3D Image Correlation Photogrammetry using the commercially available system ARAMIS. The paper also describes the experimental procedure to conduct measurements of localised deformations and strains using ARAMIS for specimens of different geometries. A comparison of experimental values from ARAMIS and those from FEA was made to validate the FEA simulation of stress softening effects. The results for different rubber specimens are presented.

A concept to increase the precision of the prediction of long-term stress relaxation in elastomers from tests conducted over short time frames is discussed. A method to separate physical and chemical relaxation processes has been developed. The basis of the method is to evaluate the continuous relaxation time spectrum for each test temperature in order to separate the relaxation processes. Subsequently a summation of all processes may be used to produce a time and temperature dependent curve fit.

Fatigue tests on ethylene propylene (EPDM) and styrene-butadiene (SBR) rubber reveal physical behavior that is not seen in conventional linear elastic solids. Uniaxial cyclical tests, using cylindrical dumbbell specimens, with the same minimum stress of zero (s(min) = 0) and varying stress amplitude (s(a)), predictably gave decreased fatigue life with increased stress amplitude and hence maximum stress (s(max)). However, tensile uniaxial cyclic tests where s(min) was increased in successive tests while alternating stress (s(a)) remained constant, produced longer fatigue lives for higher values of s(max).EPDM and SBR compounds were chosen for the tests because they do not strain crystallize during deformation. Consequently, this phenomenon has no influence. The results show that s(max) can not be used as criterion to predict fatigue life of elastomers. Preliminary evaluation of recorded data of stress vs. strain gave evidence that energies control the fatigue life rather than stress and strain. Experimental results on filled and unfilled rubber materials are evaluated and discussed as well as the consequences on predictions of component properties.