Highly attenuating tracer fibers for fiber orientation determination in short-fiber reinforced plastics

Due to their high specific stiffness and strength by low production costs short fiber reinforced plastics (sFRP) replace increasingly common materials like steel or aluminum in technical devices. Even if sFRP act homogeneously as a material on a macroscopic level, anisotropies are formed on a microscopic level due to the fiber morphology (orientation, length and volume content). As a result, components made from sFRP have lower strength and stiffness at weld lines or differences in the thickness, which can lead to component failure. Therefore, knowledge of the fiber morphology in a sFRP is essential for the design of components. One way to determine the fiber morphology is computed tomography (CT). Due to the small fiber diameters of a few micrometres (~7-20 μm), the field of view of the tomography is reduced because of the necessary high magnification. As a result, standard CT systems can only be used to examine representative, destructively obtained samples from the component and fiber morphology of components with larger volumes cannot be analysed non-destructively. In this work, an approach is investigated in which a few parts per thousand of strongly attenuating tracer fibers are added to the reinforcing fibers in the plastic, resulting in an increase in the contrast-to-noise ratio (CNR). This allows the geometric magnification to be reduced and a larger field-of-view to be achieved. The aim of the study is to examine different tracer fibers and evaluate their suitability as tracer fibers.