Nanoscale in situ observations of crack initiation and propagation in carbon fiber/epoxy composites using synchrotron radiation X-ray computed tomography

• Published in: Composites science and technology 2020-09, Vol.197, p.108244, Article 108244
• Main Authors: Watanabe, Toshiki, Takeichi, Yasuo, Niwa, Yasuhiro, Hojo, Masaki, Kimura, Masao
• Format: Article
• Language: English
• Subjects: Carbon fiber reinforced plastics; Carbon fibers; Carbon-epoxy composites; Computed tomography; Crack; Crack initiation; Crack propagation; Crack tips; Cracks; Debonding; Deformation; Epoxy resins; Fiber/matrix bond; Nondestructive testing; Plastic deformation; Spatial resolution; Synchrotron radiation; Synchrotrons; Thickness
• ISSN: 0266-3538; 1879-1050
• DOI: 10.1016/j.compscitech.2020.108244

The crack initiation and propagation under the application of opening load were analyzed in situ using nondestructive synchrotron radiation X-ray computed tomography (nanoscopic SR X-CT) with a spatial resolution of ~50 nm. The results show that the voids and cracks initiation are not only the result of local stresses but also are due to two competing nanoscale mechanisms, that is, fiber/plastic interface debonding and in-resin crack initiation. In the “thin” epoxy region in which the resin thickness between the adjacent carbon fibers is small, cracks propagate mainly by debonding along the carbon fiber/epoxy interface. In the “thick” epoxy region in which the resin thickness between the carbon fibers is large, cracks propagate through the extensive plastic deformation of the epoxy resin, and the propagation mechanism largely depends on the resin thickness, which affects the plastic deformation behavior of the epoxy around the crack tip. Voids (sub-μm) often form in front of the crack tip and merge with the propagating cracks. Nanoscopic SR X-CT provides indispensable information on these nanoscale mechanisms, which cannot be obtained with traditional methods, including macroscopic observations and mechanical theory. These nanoscale mechanisms are essential for the mechanical modeling and analysis at multi-scales. [Display omitted] •Crack initiation and propagation in CFRP was observed non-destructively in situ.•The 3D nanoscale image datasets were acquired using X-ray computed tomography.•Two datasets of reconstructed and segmented images were captured.•The data provides a valuable and unique insight for the future design of CFRPs.