Investigating the role of hierarchy on the strength of composite materials: evidence of a crucial synergy between hierarchy and material mixing

Abstract

This is an author version of the contribution published on:Questa è la versione dell'autore dell'opera: [Nanoscale, 2012,4, 1200-1207, DOI: 10.1039 AbstractNatural materials are often organized in complex hierarchical architectures to optimize mechanical properties. Artificial bio-inspired materials, however, have thus far failed to successfully mimic how these architectures improve material characteristics, for example strength. Here, a method is proposed for evaluating the role of hierarchy on structural strength. To do this, we consider different hierarchical architectures of fiber bundles through analytical multiscale calculations based on a fiber bundle model at each hierarchical level. In general, we find that an increase in the number of hierarchy levels leads to a decrease in the strength of material. However, when a composite bundle with two different types of fibers is considered, an improvement in the mean strength is obtained for some specific hierarchical architectures, indicating that both hierarchy and material "mixing" are necessary ingredients to obtain improved mechanical properties. Results are promising for the improvement and "tuning" of the strength of bio-inspired materials.

Self-Healing of Hierarchical Materials

“…Equation 12 can also be generalized to the case of a healing agent with different mechanical characteristics (E 2 , m 2 , and ε 2 ) from those of the original material (E 1 , m 1 , and ε 1 ), usually with ε 2 < ε 1 . This amounts to modeling a heterogeneous material, as discussed in, 27 with the percentage of the two phases varying with strain, and therefore damage level. Let us suppose that the specimen is made up initially only of type 1 fibers and that it heals only with type 2 fibers.…”

“…30 This model has recently been applied to heterogeneous materials, constituted of fibers with different mechanical characteristics, to determine the influence of hierarchy and material mixing in the optimization of the global material properties. 27 In spite of its simplicity, the HFBM can capture many important aspects of damage phenomena in heterostructured materials, and SH can be easily included in the model. This can be done by replacing fractured fibers with intact ones having appropriate mechanical properties, volume fractions, replacement rates and locations as damage evolves during simulations.…”

Systematic numerical investigation of the role of hierarchy in heterogeneous bio-inspired materials

“…With this model we also studied the strength and toughness of nanotube-based composites, starting from the properties and volume fractions of the fragile and ductile constituents (Bosia et al, 2010). In recent work, we addressed the issue of the synergy between hierarchy and material mixing to enhance the mechanical performance of composites, finding evidence that some hierarchical configurations lead to an improvement with respect to the non hierarchical case (Bosia et al, 2012) An important numerical study of damage evolution in hierarchical FBMs was also recently carried out by Mishnaevsky (Mishnaevsky, 2011).…”

Fatigue of self-healing hierarchical soft nanomaterials: The case study of the tendon in sportsmen

“…1: from tissue level (~ cm), to collagen fibres (~ mm in length, ~ m in diameter), to collagen fibrils (~ m in length, ~ 100 nm in diameter), to collagen molecules (~ 300 nm in length, ~ 1 nm in diameter). Therefore, as in previous studies, we simulate their mechanical behaviour using a hierarchical fibre bundle model (HFBM) 18,19 which extends the classical fibre-bundle model 16 , adding hierarchical and self-healing effects. The HFBM procedure consists in discretizing a specimen in arrays of fibres arranged in series and parallel and assigning them statistically distributed fracture strengths, using a Weibull distribution 29 .…”

“…Thus, a fibre bundle model-like approach 16 with the inclusion of hierarchy and self-healing is ideally suited to simulate the mechanical 5 behaviour of these biological structures. In previous work, we introduced such a Hierarchical Fibre Bundle Model (HFBM) 17,18 coupled with self-healing 19 to study the effects of material regeneration on the strength and toughness of hierarchical composite materials.…”