Exploiting nacre-inspired crack deflection mechanisms in CFRP via micro-structural design

Abstract

In this paper, a bio-inspired carbon-fibre/epoxy composite with nacre-like tiled microstructure is designed, synthesised and tested. Analytical models are developed to predict the energy dissipation and crack deflection properties of such composite, and the predictions for the stress-strain response during tile pull-out are validated against direct numerical simulation. Suitable configurations for tile geometry with interlocks are then identified (with dimensions of the order of 0.6 mm) and used for the subsequent prototyping. In-situ three-point bend tests are then carried out in a SEM environment, showing the capability of the interlocking micro-structure in deflecting the crack, avoiding sudden failure in the most highly loaded cross-section of the specimen. The results suggest that further damage diffusion could in principle be achieved by additionally modifying the interface between tiles

Increasing damage tolerance in composites using hierarchical brick-and-mortar microstructures

“…Parametric study on geometry of level-0 bricks (l 0nom = 460 µm, Table 2: Material properties of the carbon/epoxy thin ply prepreg used in the models and the experiments (Narducci andPinho, 2017, Skyflex, 2015). Superscripts 'b', 'm', and 'p' refer to the 'brick', 'matrix', and 'ply' properties respectively.…”

“…Gorbatikh et al (2010) showed, with their model, that carefully engineered hierarchical microstructures (with different sizes of inclusions) could eliminate the stress concentrations at the larger inclusions, hence changing the failure mechanism to a more stable one. Experimentally, nacre-like synthetic composites achieved a 700-fold increase in the toughness of the brittle constituent (Mirkhalaf and Barthelat, 2015), and crack deflection capabilities (Narducci and Pinho, 2017). Other synthetic hierarchical discontinuous composites displayed damage diffusion, preventing catastrophic failure and increasing damage tolerance (Mirzaeifar et al, 2015).…”

“…The "bottom-up" strategy creates the composite by assembling the different constituents together; this strategy includes, amongst others, multimaterial 3D printing (Mirzaeifar et al, 2015) which provides fast prototyping of samples, and polymer-coating process methods (Brandt et al, 2013) suitable for large-scale production. The second approach is the "top-down" strategy, in which an existing block of material is modified to create the discontinuities and hierarchies in the microstructure; this includes 3D laser engraving (Mirkhalaf and Barthelat, 2015) and laser micro-cutting of prepregs (Bullegas et al, 2016, Narducci andPinho, 2017).…”

Realising damage-tolerant nacre-inspired CFRP

“…Nacre-inspired CFRP architectures were also explored by Narducci and Pinho [25,26], who designed an interlocking micro-structure of bowtie-shaped carbon/epoxy tiles. In that work, it was demonstrated that such micro-structure was able to achieve crack deflection and crack bridging (two important toughening mechanisms of nacre), avoiding sudden failure in the most loaded part of the structure; however, complete diffusion of damage, which is the main energy dissipation mechanism of nacre [27], was not achieved.…”

“…These values are taken from Ref. [26] and correspond to a geometry suitably designed to avoid tile failure and promote damage diffusion.…”