A2/II Fiber and interphase modification for energy adsorption at high strain rates
Within the first cohort, both the mechanical properties (variation of strength by adjusting the drawing ratio, cross-sectional geometry) and the chemical functionalities at the surface of polymer fibers and AR glass fibers were systematically investigated by conducting own spinning experiments. Furthermore, it was possible to achieve a particularly homogeneous polymer application on the fibre surface by a dip-coating process for single fibres. By this approach the influence of the chemical/ physical properties of the coating on the fibre-matrix interaction could be separated from roughness effects in micromechanical tests. The results revealed that surface roughness (as a precondition for inducing mechanical interlocking) and degree of cross-linking are important properties for the development of fibre-reinforced, fracture-resistant concrete composites under impact load (Fig. 1).
Fig. 1: a) Force-displacement curve of sized PP-fibres pulled-out of cementitious matrix during dynamic single fibre pull-out test; b) SEM images, top: deformed, rough fibre surface in the case of increasing pull-out force, below: undeformed , smooth fibre surface for low pull-out forces
Fig. 2: Approach for the fibre and interphase modification , a) application of particles by polymer dispersions; b) introduction of particles by a bicomponent-spinning process
It is the aim of the project to develope and implement concepts for a targeted interphase design to increase the impact resistance based on high plastic deformation of polymer fibers or in the polymer-based interphase in case of high-modulus fibers. The mechanical interlocking, which leads to shearing (high plastic deformation) of the polymer fibers, is initiated by the application of particles (e.g. aluminium oxide) from polymer dispersions (Fig. 2a), while the influence of particle type, particle size and application are systematically investigated, as well as the influence of the mineral-bonded matrix (e.g. geopolymers). The incorporation of particles into the polymer and the subsequent processing in the bicomponent-spinning process will also be studied as a possible solution (Fig. 2b). A similar approach is followed for increasing the roughness of coatings for carbon fibers, here also the degree of chemical crosslinking in the coating is varied. This approach will later be transferred to textile reinforcement structures and investigated on concrete composites under high strain rates.