Biological and Biomimetic Materials Laboratory, Center for Sustainable Materials (SusMat), School of Materials Science and Engineering, Nanyang Technological University (NTU), 50 Nanyang Avenue, 639798, Singapore.
School of Mechanical and Aerospace Engineering, NTU, 50 Nanyang Avenue, 639798, Singapore.
Acta Biomater. 2021 May;126:339-349. doi: 10.1016/j.actbio.2021.03.025. Epub 2021 Mar 13.
The dactyl club of stomatopods is a biological hammer used to strike on hard-shell preys. To serve its function, the club must be imparted with a high tolerance against both contact stresses and fracture. While the contact mechanics of the club has been established, fracture toughness characterization has so far remained more elusive and semi-quantitative using nanoindentation fracture methods. Here, we used microcantilever fracture specimens with a chevron-notched crack geometry to quantitatively evaluate the fracture response of the impact region of dactyl clubs. The chevron-notched geometry was selected as it minimizes surface-related artefacts due to ion milling, and further allows to carry out fracture tests on samples free of pre-cracks with stable crack propagation even for brittle materials. Both linear elastic as well as elastic-plastic fracture mechanics methods, together with finite element modelling, were employed to analyse the fracture data. We find that crack-tip plastic dissipation is the main mechanism contributing to the fracture properties of the dactyl club material. Our study also suggests that the chevron-notched crack geometry is a suitable method to quantitatively assess the fracture toughness of hard biological materials. STATEMENT OF SIGNIFICANCE: Characterizing the fracture resistance of biomineralized structures is essential to draw their structure-properties relationships. Yet measuring the fracture properties of such materials is often hampered by their small size and irregular shape. Indentation fracture is used to circumvent these issues but does not discriminate between the elastic and elastic-plastic contributions to the fracture resistance. The dactyl club "hammer" of mantis shrimps is a biological material whose fracture properties are central to its function. A microfracture study was conducted using microcantilever specimens with chevron-notched crack geometry to assess the fracture toughness. Adopting linear elastic and elastic-plastic fracture mechanics protocols, we find that plastic dissipation is the major contribution to the fracture response of the hypermineralized impact region of the dactyl club.
螳螂虾的肢夹是一种用于击打硬壳猎物的生物锤。为了发挥其功能，肢夹必须具有很高的耐接触应力和断裂的能力。虽然肢夹的接触力学已经建立，但迄今为止，使用纳米压痕断裂方法，其断裂韧性的表征仍然更加难以捉摸和半定量。在这里，我们使用具有 V 型缺口裂纹几何形状的微悬臂梁断裂试样来定量评估肢夹冲击区域的断裂响应。选择 V 型缺口几何形状是因为它最大限度地减少了离子铣削引起的表面相关伪影，并且进一步允许在没有预裂纹的情况下对脆性材料进行断裂试验，并且稳定的裂纹扩展。线性弹性和弹塑性断裂力学方法以及有限元模拟都被用于分析断裂数据。我们发现，裂纹尖端的塑性耗散是导致肢夹材料断裂性能的主要机制。我们的研究还表明，V 型缺口裂纹几何形状是定量评估硬生物材料断裂韧性的一种合适方法。
表征生物矿化结构的抗断裂性对于绘制它们的结构-性能关系至关重要。然而，测量这些材料的断裂性能通常受到其小尺寸和不规则形状的阻碍。压痕断裂被用于规避这些问题，但不能区分断裂阻力的弹性和弹塑性贡献。螳螂虾的肢夹“锤子”是一种生物材料，其断裂性能对其功能至关重要。进行了微断裂研究，使用具有 V 型缺口裂纹几何形状的微悬臂梁试样来评估断裂韧性。采用线弹性和弹塑性断裂力学协议，我们发现塑性耗散是肢夹的超矿化冲击区域断裂响应的主要贡献。
