In-situ 3D fracture propagation of short carbon fiber reinforced polymer composites

This paper explored the 3D progressive fracture process of a short carbon fiber reinforced polymer composite under uniaxial tensile loading via high-resolution in-situ micro X-ray computed tomography (μXCT). Microstructural features extracted from the μXCT images were analyzed with the Halpin-Tsai model, laminate analogy approach, and shear-lag model to calculate the mechanical properties and interpret the different fracture morphologies and progressions observed in the “skin-core-skin” structure. The in-situ μXCT scanning revealed a clear fracture progression in the skin layer, which was defined by four stages, i.e., nucleation of small pores at fiber ends, coalescence of pores, initiation of cracks, and propagation of cracks until fracture, whereas no significant fracture feature was found in the core layer. To analyze the difference in the fracture mechanisms in the skin and core layers, the maximum fiber normal stress and average interfacial shear stress were calculated from the microstructural features. The results were also confirmed by the 3D strain distribution quantified via a volumetric digital image correlation method. It was determined that the dominant fracture mechanism in the skin layer was fiber pull-out, rather than fiber breakage, as a consequence of pore formation at the fiber ends; its extent mainly depended on the fiber length and orientation angle. Fiber/matrix debonding was the main fracture mechanism in the core layer, which resulted from the propagation of cracks initiated from the skin layer.