Direct observation and measurement of fiber architecture in short fiber-polymer composite foam through micro-CT imaging

A non-destructive X-ray imaging technique was used to determine internal structure in a polymer foam reinforced with short fibers. The technique, known as micro-CT (for computerized tomography), was used to measure the fiber length distribution (FLD) and fiber orientation distribution (FOD), two parameters that are critical to the behavior of short-fiber-reinforced composites. Phenolic foam reinforced with short glass fibers was used as an exemplar to demonstrate the potential of this technique, exploiting the large difference in density between the two components. Direct 2D and 3D images were generated in which individual fibers were clearly resolved, along with portions of the foam structure. The images were analyzed using computer software to obtain quantitative FLD and FOD data. A distinct preferred orientation of fibers was revealed that was attributed to shear flow during foam expansion. For quantitative analysis of microstructure in short fiber composites, the micro-CT technique affords numerous advantages over the conventional approach of parallel dissection followed by image analysis of polished surfaces, and may be useful for determining FLD and FOD in polymer composites with dense matrices.