MODELING AND OPTIMIZATION OF NACRE-LIKE MATERIALS
- Natural or biological material are made from weak constituents that have evolved hundreds of millions year thus having outstanding mechanical properties
- Biological Material vs. Engineering Material
- Nacre, which is an inner layer in sea shells, is composed of microscopic mineral polygonal tablets bonded by a tough biopolymer (organic layer)
-95% mineral = calcium carbonate (aragonite CaCO3)
-5% proteins and polysaccharides (Chitin)
- Nacre has a remarkable toughness due to sliding and waviness of the tablets
- Mimicking the high toughness and stiffness into engineering materials is desired.
- Models in literature assumes the tablets are flat and don’t account for tablet waviness.
- Designing of bio-inspired materials is done currently by trial and error.
- The improvement in toughness relative to its main constituent is not as in biological materials.
- No clear way of selecting materials and geometry of the structure.
- Build an improved model of a biological hard material (Nacre) to predict the mechanical properties in order to aid in designing of a bio-inspired material.
- The waviness should be included in the model.
- The model should predict stiffness & toughness.
- The model should be able to predict the optimal material and geometry of the tablets and interface (matrix) to produce the optimal mechanical properties (stiffness, strength and toughness)
WAVINESS STIFFNESS & TOUGHNESS MODEL
- Representative volume element (RVE) that includes waviness as dovetail feature.
- Stress- strain equation is
- Toughness is quantified using J-integral
- Bridging and process zone: toughening mechanisms are considered
- Nacre has shown to exhibit a raising resistance curve (R-curve)
- R-curve is given by
- R-curve plot comparison
- Nacre like-materials can replace materials and composites in applications that require high stiffness and toughness with less weight in areas such as material science, biomaterials development, civil and nanotechnology
- Nacre-like materials and coatings have been developed for biomedical applications such as development of better performance implant materials.
- Researchers are looking into using cement paste, which is concrete’s binding ingredient, with the structure and properties of natural materials such as nacre, bone and deep-sea sponge.
OPTIMIZATION OF NACRE-LIKE MATERIALS
- Multi-objective Optimization Formulation
- Genetic Algorithm based on no-dominated sorting genetic algorithm II (NSGA II) is used
- MATLAB optimization tool box is used to solve the optimization problem
- Sample of solution were plotted in Ashby charts indicating the performance of nacre-like material relative to existing engineering materials
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