A Novel Layer-by-layer Biomimetic Structure: Structural Design, Mechanical Properties and Failure Mechanism

Description

Nature develops crack-resistant structures. One example is the natural teeth which are formed by enamel, dentin and dentin-enamel-junction (DEJ) (Figure 1a). Although small cracks could generate in the brittle enamel, most of them are arrested at the enamel-dentin interface (Figure 1b). Bulk failure of the teeth is therefore prevented. More dramatically, the structure could survive millions of cycles of occlusal loading with the existence of these cracks [Lin et al., 1994; Imbeni et al., 2005; Chai et al., 2009]. Inspired by the remarkable crack-resistance of natural teeth, many efforts were devoted to develop multilayer structures that are formed with hard top and durable substrate [Lawn, 2002; Lawn et al., 2004; Lee et al., 2002; Huang, et al., 2007a, 2007b]. However, this biomimetic endeavor encounters long-standing difficulty. Although having similar structures, none of the man-made multilayers could provide crack-resistance that is comparable to nature teeth. This difficulty is caused by many reasons. Lack of guidance upon structural design and inadequate information about failure mechanisms are among the most important ones.In this project, a novel layer-by-layer biomimetic structure will be developed by learning from the comprehensive microstructure of natural teeth. In the new structure, material properties will change gradually from top to bottom and there will be no distinct top or substrate layers. The gradually changing structure has the potential to minimize the stress concentration and crack driving force in the structure [Hauber, 2009; Hill and Lin, 2002; Hill et al., 2002]. Then, viscosity-related failure mechanism of this new structure will be investigated. Mechanical experiments will be performed under macro-, micro- and nano- scales to explore the modulus, viscosity, fracture toughness and other physical response of the structure. State-of-the-art microscopes such as atomic force microscope (AFM), scanning electron microscope (SEM) and transmission electron microscope (TEM) will be adopted to characterize the fracture surfaces and crack paths. In addition, non-linear finite element analysis (FEA) will be carried out to simulate, verify and promote the design. A successfully validated computational framework could provide guidance to the future design of crack-resistant layer-by-layer structures. The project will not only benefit the development of new dental structures, but also provide a light-weighted and tougher layer-by-layer structure for a broader class of engineering devices such as wind blades, printed circuit boards and automobile parts etc. The methodologies used in this project could also benefit the research and development on diversified biomimetic projects.