Abstract
In this work, the underlying micro-damage mechanisms of randomly oriented short fibre-reinforced composites were revealed based on real internal microstructural characteristics obtained by high-resolution (0.7 μm/pixel) synchrotron radiation X-ray computed tomography (SR-CT). The special ‘pore dominant micro-damage processes’ were directly observed through SR-CT three-dimensional reconstructed images, which were different from the well-known ‘fibre breakage dominant failure mode’. The mechanisms of pore formation and pore evolution were further investigated on the basis of the microstructural parameters extracted from the SR-CT results. On one hand, the pore formation mechanism caused by shear stress concentration was proposed by combining the shear-lag model with the microstructural parameters obtained from the experiment, including the fibre length and orientation angle. On the other hand, the ‘fibre-end aggregation-induced pore connection’ mode of crack initiation was proposed through a composites model, which considered the parameters of real internal microstructure, including the critical value of the distance between neighbouring fibre ends and the number of neighbouring fibre ends. The study indicated that the shear stress concentration was significant in the region with a large number of neighbouring fibre ends, thus causing pore connection and crack initiation.
Highlights
In this paper, the underlying micro-damage mechanisms of randomly oriented short fibre-reinforced composites were revealed, for the first time, on the basis of real internal microstructure characteristics obtained by high-resolution (0.7 μm/pixel) synchrotron radiation X-ray computed tomography (SR-CT) experiments
The underlying micro-damage mechanisms in randomly oriented short-fibre composites were revealed by precise SR-CT experimental characterisation of the relation between real internal microstructural characteristics and micro-damage evolution
The pore formation mechanisms caused by shear stress concentration were proposed on the basis of the special contact relationship between pore formation and fibre ends obtained from the SR-CT experiment
Summary
The underlying micro-damage mechanisms of randomly oriented short fibre-reinforced composites were revealed, for the first time, on the basis of real internal microstructure characteristics obtained by high-resolution (0.7 μm/pixel) SR-CT experiments. We proposed a pore formation mechanism caused by shear stress concentration by combining the shear-lag model with the fibre length and orientation angle. The value of shear stress at fibre ends, which caused pore formation, was determined by the fibre length and orientation angle. We proposed the ‘fibre-end aggregation-induced pore connection’ mode of crack initiation through a composites model that demonstrated the significant influence of the microstructural parameters obtained from the experiment. Such microstructural parameters included the number Ne of neighbouring fibre ends and the critical value le of the distance between neighbouring fibre ends. This finding was confirmed in our experiment by the decreased critical value of the composite after oxidation treatment, considering that oxidation treatment improved the interfacial shear strength
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