Modulating Intrinsic Brittleness Impacts Damage Mechanisms in Bioinspired Lamellar Materials

Bouligand or periodic lamellar structures are prevalent in nature and possess remarkable toughness properties. The intrinsic properties of their constituent materials, which can range from non-mineralized collagen-based fish scales to fully mineralized cortical bone, significantly affect their damage-resistant behavior. These hierarchical micro-structured materials serve as a valuable source of inspiration for the development of novel materials, particularly in the field of bio-inspired design. Despite the considerable attention given to replicating their intricate geometrical arrangements, the role of the constituent material itself remains relatively unexplored. Investigating how different base materials within complex arrangements, such as Bouligand patterns, could unlock new avenues for creating high-performance, damage-resistant materials. This understanding is crucial, especially in advanced manufacturing processes like additive manufacturing, where material choices are often limited yet must meet stringent performance demands.<br/>Using computational modelling, we investigate the crack and damage behaviour in periodic-lamellar materials by systematically modulating the intrinsic toughness of their constituent materials. Our approach employs a phenomenological elastic-plastic finite element analysis (FEA) model to predict the progressive evolution of damage and failure. This is achieved by varying the parameter Γ, which represents the non-reversible fracture energy or crack growth resistance of the constituent material, while keeping other modelling parameters, such as elasticity and plasticity, constant. By isolating the influence of Γ, we can accurately study how material’s intrinsic brittleness or toughness impacts overall fracture behaviour. The results reveal that fracture mechanisms in periodic-lamellar structures vary significantly with Γ. We demonstrate that the improvement in strength due to the hierarchical structuring is most pronounced for materials with smaller Γ values, i.e., more brittle constituents. Conversely, for less brittle materials, the structural arrangement has a minimal effect on improving their strength. This suggests that brittle materials, when patterned in Bouligand-like architectures, benefit more from the hierarchical structuring in terms of load-bearing capabilities, while tougher materials may not see as much of a performance boost from this arrangement.<br/>Our analysis identifies three distinct fracture regimes based on the intrinsic fracture energies of the base material. In the lower range of Γ, a micro-cracking dominated regime is observed, where cracks bifurcate and propagate with minimal plastic dissipation at the softer regions of the structure. At medium values of Γ, we observe a unique mechanism driven by localized plasticity, where the strong layers are shielded by significant plastic dissipation occurring in the preceding softer regions. In this regime, the crack growth resistance plays a more pivotal role than the crack driving force. Interestingly, this medium Γ regime exhibits the most significant toughness improvements, as the balance between brittleness and plasticity seems optimal for resisting fracture. In contrast, at larger Γ values, the fracture behavior is dominated by the properties of the constituent material itself, and both the stiff and soft layers undergo significant plastic deformation and fracture. <br/>These findings highlight the complex interplay between material properties and structural architecture, offering valuable insights for the design of bio-inspired tough materials. By strategically manipulating the intrinsic brittleness of base materials, it becomes possible to fine-tune the structural arrangements and optimize the fracture mechanisms, enabling the creation of materials with superior damage resistance and mechanical performance.