Mechanics and Composite Materials
The microscopic structure of polymeric materials has a significant impact on their macroscopic properties. A better understanding of the structure-properties relations offers the possibility of a dedicated materials design and optimisation, where in multicomponent materials also interfaces and morphology play a major role.
In particular mechanical properties are important in most polymer applications, which are in the focus of the work. Structural investigations are performed at different levels from a nanometer scale to macroscopic dimensions, and a direct correlation between structure, conformation, orientation, morphology, phase compositions, homogeneity, dispersion etc. and important properties like toughness, strength, adhesion is tried to be established.
During Online-structure characterisation by x-rays it is possible to follow directly temperature dependent structural changes during deformation and fracture. Due to the necessary beam intensity and time resolution the investigations were performed mostly with synchrotron radiation (DESY, Hamburg). Using fibre symmetry of the specimen segment length distributions were estimated from the pattern. So it was possible to follow the strain induced crystallization of natural rubber with high time resolution (about 10 ms) and scanning around a crack tip with high space resolution (about 20 microns).
For practical reasons it is necessary to perform measurements also under application-relevant loading conditions and to describe material behaviour by constitutive laws. Therefore in a well-equipped testlab a wide number of devices is available for quasistatic as well as dynamic load, at room temperature as well as at elevated temperature.
Mainly for elastomers a the dynamical characterization under uniaxial and biaxial load with optical measurement of 2d-strain-fields is important for the description of deformation and fracture behaviour.