1. Finite Element Modeling of Nacre
Austen Motily with Dr. Mark Garnich
Sponsored by the Department of Mechanical
Engineering and EPSCoR

2. Nacre Also known as mother of pearl
Composite material found in mollusk shells
Two phases
Aragonite
Organic protein matrix
Barthelat et al. [1]

3. Nacre Unique periodic arrangement About 95% aragonite
“repeating” structure
Hexagonal platelets
About 95% aragonite
Brittle
Doesn’t absorb much energy
About 5% organic protein
Ductile
Easily deformed
Barthelat et al. [1]

4. Fracture Toughness
The amount of energy a material can absorb before it breaks
Nacre has a high fracture toughness
95 % of the nacre is not very tough
The unique arrangement of nacre results in its increased toughness

5. Why is Toughness important?
Materials must be resistant to flaws
Tough materials resist rapid crack propagation
Energy absorption is important in structural stability
Katti et al. [2]

6. Finite Element Modeling
Create a model of the structure
Separate the model into small elements
Use the finite element method to predict material behavior
Analyze the results
Abaqus® was used for this research
Marks, Laurence [3]

7. Representative Volume Element (RVE)
Nacre platelets are about one micron thick
Would be almost impossible to model thousands of layers of Nacre
Create a small volume representative of overall behavior
Zuo and Wei [4]

8. Representative Volume Element (RVE)
Difficulties
Conceptually more difficult
Must implement correct boundary conditions
Have to achieve symmetry

9. Two-Dimensional (2D) Model
Create a model to compare to results of Zuo and Wei
Tension test
Simplify as much as possible
Start with elastic behavior
Implement plastic behavior of organic protein phase
Zuo and Wei [4]

10. Results of 2D Elastic Simulation
Verify correct geometrical behavior
Achieve symmetry

11. Results of 2D Plastic Simulation
Protein: elastic linear-plastic material
Equivalent to model of Zuo and Wei

12. Results of 2D Plastic Simulation
Similar general behavior

13. Three-Dimensional (3D) Model
Include depth in the model
Elastic-plastic behavior of protein
Verify correct implementation of boundary conditions
Stress-strain behavior should be the same

14. Results of 3D Simulation
Same geometrical behavior as 2D simulation

15. Results of 3D Simulation

16. Results of 3D Simulation

17. Comparison of 2D and 3D Simulations
Same stress-strain behavior for the two simulations

18. Comparison of Stress-strain curves
Plastic portion slopes are different

19. Discrepancy Between Stress Strain Curves
Distribution of stress along vertical axis
Protein behavior converted from shear stress/strain
Abaqus® requires normal stress-strain behavior for input
Difference in slope of plastic portion of stress-strain curve is too large to be attributed to these factors

20. Verification Using the Mathematical Model
Solve the differential equation used by Zuo and Wei
Use Matlab® to solve the differential equation
Create stress-strain curve and compare to results of Zuo and Wei

21. Verification Using the Mathematical Model
Similar to Abaqus® simulation results

22. Next Steps Simulate nacre under shear loading
Compare with experimental results from Menig et al.
The tension test produced a lot of shearing action in model
New simulation will contain different boundary conditions indicative of a shear simulation
Menig et al. [5]

23. Next Steps
More advanced models that incorporate the complex hexagonal platelet arrangement
Implement a more realistic elastic- plastic model for the organic protein phase
Simulate other loading scenarios such as bending or compression
Menig et al. [5]

24. References
Barthelat F, Dastjerdi AK, Rabiei R An improved failure criterion for biological and engineered staggered composites. Journal of The Royal Society Interface 10, 1-10.
Katti DR, Katti KS, Sopp JM, Sarikaya M D Finite Element Modeling of Mechanical Response in Nacre-Based Hybrid Nanocomposites. Computational and Theoretical Polymer Science 11,
Marks L Bolted Joints in Finite Element Models. SSA Limited.
Zuo S, Wei Y Microstructure observation and mechanical behavior modeling for limnetic nacre. Acta Mechanica Sinica 24,
Menig R, Meyers MH, Meyers MA, Vecchio KS Quasi-Static and Dynamic Mechanical Response of Haliotis Rufescens (Abalone) Shells. Acta Materialia 48,