Micro-CT Imaging of Fibers in Composite Laminates under High Strain Bending

To be able to track the deformation of fibers in composite laminates subject to high strain bending and to study any changes that occur due to elevated temperature hold, an experimental technique using micron scale X-ray computed tomography (micro-CT) was developed and is reported here. A lab based X-ray micro-CT system with resolution as low as 0.7 μ m was used to scan an approximately 0.76 × 0.76 × 0.27 mm volume of a 0.27 mm thick unidirectional carbon fiber/epoxy matrix composite laminate. Long scans of 16 hours at low energy, 40 kV, were needed to yield low noise, clear CT images. The laminate is bent to a radius of curvature of approximately 8.2 mm and held statically in a 3D printed fixture. Since the fixture is in the beam path it is important that it have low and uniform X-ray absorption. Several materials were tried, resulting in the choice of polyamide for the 3D printed fixture. Treating fiber cross sections as particles and adapting an algorithm designed for tracking particle trajectories, individual fibers in the deformed state are identified and their coordinates mapped out. Analysis of the fibers shows no measurable change to the fiber curvatures before and after being held at 80 ∘C for one hour.