In situ analysis of three-dimensional microcrack propagation in cross-ply laminates using synchrotron radiation X-ray computed tomography

This study utilized synchrotron radiation X-ray computed tomography to investigate the initiation and propagation of microcracks in cross-ply carbon fiber-reinforced polymer (CFRP) laminates under mechanical loading. Initially, static tensile loads were applied to detect microcracks within a ply thickness of 160 μm. The crack propagation was subsequently characterized, extending across adjacent carbon fibers and along the interfaces of individual fibers into the material's interior. The experiment was repeated with cyclic loading, where the laminates were imaged periodically. Analysis of the images revealed the presence of microcracks and provided insights into their progression from the point of initiation. Notably, microcracks exhibited the initiation toward the interior of the material rather than across the neighboring carbon fibers, whereas their propagation is more significant across the adjacent carbon fibers particularly under the static loading. Under cyclic loading, however, the crack propagation toward the interior of the material was more pronounced, implying different propagation behavior than when under static loading. These findings were also validated through the distribution of energy release rate and stress triaxiality along the crack tip calculated by finite element analysis.