The effectiveness illustration of biomimetic fastening of composite parts

One of the main problems in designing composite structures is the creation of reliable fastening methods, since traditional drilled holes destroy load-bearing fibers, leading to significant stress concentration and reduced strength. The aim of this work is to develop and illustrate a bio-inspired method for fastening composite parts by creating a curved reinforcement structure that mimics the knot zone in wood. It is shown that an iterative algorithm for computer modeling of fiber trajectories «flowing» around the hole, allows the construction of a reinforcement structure in which the «fiber overload coefficient» is only 1.3 instead of a stress concentration coefficient of about five in a unidirectional carbon fiber plate with a circular hole. Experiments on wooden samples with removed knots and drilled holes, as well as on composite samples with curved reinforcement made using 3D printing, confirmed the effectiveness of the proposed approach. Preserving the reinforcement structure in the knot area means that the hole from the removed knot does not affect the strength at all, and failure occurs away from the hole. The results confirm the promise of using bio-like joints to significantly increase the load-bearing capacity and durability of composite fasteners, which is especially important for large aerospace structures.

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