Strengthening of Composite Holes Inspired by Encased and Intergrown Knots

Tree knots are generally considered defects in wood, but how the surrounding structures of the defects affects strength of wood has not been studied. Here the mechanical properties of static compression and hole bearing tests were designed for encased knots and intergrown knots, and the strengthening mechanism of streamline tissue and connecting interface was analyzed by finite element modeling. And the two reinforced structures were applied to composite structural holes and connecting holes, which significantly improved open hole compressive strength and hole bearing strength. And the finite element models for two kinds of composite hole were created to analyze how the stress field around the reinforced structure strengthens the composite. Both the experimental results and the finite analysis results show that the streamline structure could effectively improve the compressive properties of composite structural holes, and the connecting interface provided a stable constraint for giving full play to the hole bearing properties of stronger materials. These two structures will provide reference for the structural design of lightweight composites.