Crack characterization of discontinuous fiber-reinforced composites by using micro-computed tomography: Cyclic in-situ testing, crack segmentation and crack volume fraction

Fiber-reinforced polymers combine the aspects of stiff fibers and light polymer matrix. The arrangement of fibers on the microstructural level significantly affects the mechanical properties on the macroscopic scale, such as stiffness and fracture toughness. Micro-computed tomography systems (mCT) enables a detailed volumetric view into microstructures in a none-destructive way. By performing mechanical test inside a mCT system, the effects of mechanical load onto the microstructure, such as damage initiation and propagation are observed in-situ. Since cyclic load is a common use case for many components, fatigue and cycle load tests are essential for material characterizing. In this contribution, the authors introduce an in-situ mCT setup for cyclic load tests. The test device is designed to generate high-resolution images, in order to observe cracks through different propagation stages. In addition, cracks are three-dimensionally segmented and a crack volume fraction definition is introduced. The presented in-situ test setup and crack characterization method are demonstrated on sheet molding compound specimen, a glass-fiber reinforced thermosetting material system.