Fatigue Behavior of a Biomimetic Ceramics/FGM/Nano-composite Multilayer

Description

Nature produces fatigue-resistant structures through multilayer design. Teeth, bone and hairare all fatigue-resistant natural structures consisting of multiple layers. More magically,nature’s long-life design philosophy is to survive the presence of cracks instead of prohibitingcracks from initiating. To mimic this superior property, a ceramics/composite multilayerstructure has been developed and widely adopted. The design is to combine the stiffnessand/or hardness with the ductility. However, this structure encounters long-standing difficultyto match the natural ones in fatigue-resistance. The difficulty arises from several aspects.First, the interfaces in ceramics/composite multilayers play the role of crack initiator andaccelerator, instead of a shielding as manifested by natural ones. Second, it is hard for peopleto fabricate fatigue-resistant individual layers. The difficulty could be due to mechanical,chemical and physical properties. Finally, fatigue itself is a notoriously difficult problemsince it is time-dependent, requires comprehensive research techniques and is cost intensive.The proposed project is to address the above problems in the scope of failure mechanics andstructural materials science. First, a biomimetic ceramics/FGM/nano-composite multilayerstructure will be fabricated and investigated for its fatigue behavior under Hertzian contactloading, where FGM stands for functionally graded material. FGM is introduced as middlelayer hoping to minimize the stress concentration between ceramic top layer and nano-compositesubstrate layers. Then, fatigue behavior and failure mechanism of each individuallayer will be investigated by multi-scale experiments. Finally, in-depth understanding uponfatigue mechanism of both individual layers and the multilayer structure will be investigatedby state-of-the-art microscopies, failure analysis assisted with finite element analysis (FEA),and damage mechanics modeling.The proposed study has following significances. First, a biomimetic FGM layer is introducedto enhance fatigue life of the multilayer structure. Second, crack growth process of a complex3-dimentional (3D) crack in ceramics/FGM/nano-composite multilayers will be observed andcharacterized. Then, fatigue behavior of each individual layer will be studied by multi-scaleexperiments aided by FEA. A novel atomic force microscope (AFM) assisted indentationexperiment, along with other micro- and macro-scale experiments, will be performed to gainin-depth understanding upon toughening mechanism of nano-composites. Finally, a newhybrid damage model will be established to capture fatigue behavior. The model will bevalidated by comparing with experimental results and then be applied to predict remaininglife of the structure. Long-term wise, the proposed project could provide guidance to thedesign of novel biomimetic multilayer structures.