A micromechanical model for bioinspired nanocomposites with interphase

The stagger-aligned structures including ‘‘brick-and-mortar’’ are well-known as a generic feature in biological tough and strong nanocomposites, leading to bioinspired high-performance composites. Experimental observations have shown that the region between the stiff reinforcements and the soft matrices is not an interface of zero thickness but a nanoscale interphase. The interphases are believed to play an important role in the overall mechanical achievements; however, related theoretical models are still yet to be developed for decoding the interphase-related mechanisms. Based on the shear-lag theory, this work establishes a theoretical model for the staggered nanocomposites explicitly considering the interphase. In particular, a compact formula of the nanocomposites’ effective modulus (E_c) is derived, clearly showing the relations to a load-sustain dominant term (E_R) and a term (E_S) reflecting the load-transfer through shear deformation, as well as other microstructural and material parameters. With comparison to results by the finite element analysis and other existing relevant models, our model exhibits superior accuracy and simplicity, as well as general applicability. Furthermore, our model reveals an interesting working mechanism of the interphase: E_c is sensitive to the interphase properties for the shear transfer parameter (β_II) being around 1.5–7.5, as the interphase undertakes both stress-transfer and stress-sustaining roles. The model and findings shed light on the role of the interphase in enhancing load-bearing biological composites and provide new insights in optimizing bioinspired nanocomposites through modulating the interphase properties.