Dr. Kalpana S. Katti

Dr. Dinesh R. Katti

Department of Civil Engineering
North Dakota State University, Fargo, ND, USA

To develop multiscale models for predicting mechanical behavior of biological materials by bridging molecular, nano to macro scale mathematical models. This research answers fundamental reasons for the extraordinary mechanical properties like toughness and strength exhibited by biological nanocomposite nacre, the inner layer of seashells.  

3D Finite Element Simulation of Nacre Micro-Architecture : Laminated Structure: Inelastic Response

RESULTS: The purely laminated structure of nacre as widely proposed would require the organic phase in nacre to have an extraordinarily high yield stress of 400 MPa. (Our discovery of platelet interlocks in 2005 will eliminate this requirement - see below)

Katti, D. R. Katti, K. S., Sopp J., and Sarikaya, M., (2001)3D Finite Element Modeling of Mechanical Response in Nacre-Based Hybrid Nanocomposites, J. Theo. Comp. Poly. Sci. 11 (5), pp. 397-404.

RESULTS: The nanoasperities or surface roughness has small contribution to the elastic modulus of nacre and almost no contribution to its yield stress. The roughness may provide better adhesion between organic phase and the mineral phase and may provide some level of confinement to the organics.

Katti, D.R., Pradhan, S.M., and Katti, K.S., (2004), Modeling The Organic-Inorganic Interfacial Nanoasperities In A Model Bio-Nanocomposite, Nacre, J. Reviews on Advanced Materials Science, n 6, 162-168.

• Design of high performance new nanocomposites taking inspiration from biological materials
• Development of computational and analytical tools for a truly simulation based design of materials
• Multiscale models for prediction of mechanical response of a variety of biological materials for applications in bioengineering

   

RESULTS: The elastic modulus of the organic phase in nacre has a magnitude much higher than that expected for typical proteins. The simulations predict elastic modulus of the order of 15 to 20 GPa for the organic phase. (This was later confirmed experimentally by another group)

Katti, Dinesh R. and Katti, Kalpana S., (2001) Modeling Microarchitecture and Mechanical Behavior of Nacre Using 3D Finite Element Techniques, Part I: Elastic Properties, Journal of Materials Science, 36 (6):1411-1417

RESULTS: The mineral contacts have minimal contribution to the elastic modulus and yield stress of nacre. In fact, the mineral contacts break long before nacre exhibits yielding. It appears the mineral contacts are present for the biological growth of nacre.

Katti, K.S., Katti, D.R., Tang, J. and Sarikaya, M.,(2005), Modeling Mechanical Responses In A Laminated Biocomposite, Part II, Nonlinear Responses And Nuances Of Nanostructure, Journal of Materials Science, n 40, 1749-1755

Scale bar: 50 nm

Discovery of Interlocks in Nacre: Key to Toughness and Strength