Fruit Walls and Nut Shells as an Inspiration for the Design of Bio-Inspired Impact-Resistant Hierarchically Structured Materials

Fruit Walls and Nut Shells as an Inspiration for the Design of Bio-Inspired Impact-Resistant Hierarchically Structured Materials

R. Seidel M. Thielen C. Schmitt A. Bührig-Polaczek C. Fleck T. Speck 

Plant Biomechanics Group Freiburg, Botanic Garden, Faculty of Biology, University of Freiburg, Germany

Foundry-Institute of the RWTH Aachen, Germany

Materials Engineering, Berlin Institute of Technology, Germany

Competence Networks Biomimetics and BIOKON, Germany

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Until today the structuring of different types of fruit walls has been used only as an inspiration for packaging when seen from a biomimetic perspective. However, by a detailed investigation of the Macadamia nut with its tough testa, Citrus maxima, possessing a large spongy mesocarp and Cocos nucifera, having a combination of a fi brous mesocarp and a tough endocarp, it becomes evident that those structures also provide excellent biological role models for impact- and puncture-resistant materials. Both Citrus maxima and Cocos nucifera are relatively heavy, lack any aerodynamic adaptation and share the same challenge of having to withstand the impact from heights of >10 m. Conducting high-speed camera-controlled free fall experiments of Citrus maxima from 6 m height, we could demonstrate a deceleration of the fruits of 3100 m/s², which corresponds to 316 g, without any visible damage of the fruit. An analysis using cyclic quasi-static compression tests of the pericarp of Citrus maxima revealed that the material behaves constant in good approximation after the fi rst loading cycle. During the fi rst cycle, almost 75% of the energy is dissipated. The pericarp of Citrus maxima is highly visco-elastic, which causes the samples within 1 min to recover 30% of their initial deformation caused by loading to 40% strain. The mesocarp of Citrus maxima is best described as an open-pore foam with a gradual increase in the pore size. Understanding the principles of as to how combining the structure and material in biological constructions yields a fully functional protection layer will allow us to construct new lightweight bio-inspired materials of high impact and puncture resistance with a combination of high energy dissipation, benign failure and almost complete recovery from large deformations.


 Biomimetics, Citrus maxima, Cocos nucifera, energy dissipation, gradual open-pore foam,  Macadamia sp.


[1] Hartung, M.E. & Storey, W.B., The development of the fruit of Macadamia ternifolia. Journal of Agricultural Research, 59, pp. 397–406, 1939.

[2] Jennings, J.S. & Macmillan, N.H., A tough nut to crack. Annals of Botany, 46, pp. 313–321, 1980.

[3] Wang, C. & Mai, Y., Deformation and fracture of Macadamia nuts part 2: microstructure and fracture mechanics analysis of nutshell. International Journal of Fracture, 69, pp. 67–85, 1995. doi:

[4] Wang, C. & Mai, Y., Deformation and fracture of Macadamia nuts part 1: deformation analysis of nut-in-shell. International Journal of Fracture, 69, pp. 51–65, 1995. doi:


[5] Mamman, E., Umar, B. & Aviara, N., Effect of moisture content and loading orientation on the mechanical properties of Balanites Aegyptiaca nuts. Agricultural Engineering International, The CIGR Ejournal 7, Manuscript FP 04 015, 2005.

[6] Ozden, K. & Alayunt, F., The determination of some physical properties of Pistachio vera L. Pakistan Journal of Biological Sciences, 9(14), pp. 2612–2617, 2006. doi:


[7] Oloso, A. O. & Clarke, B., Some aspects of strength properties of Cashew nuts. Journal of Agricultural Engineering Research, 55, pp. 27–43, 1993. doi: 1993.1030

[8] Lieberei, R. & Reisdorff, C., Nutpfl anzenkunde, Georg Thieme Verlag: Stuttgart, 2007.

[9] Varma, D.S., Varma, M. & Varma, I.K., Coir fi bers: Part I: effect of physical and chemical treatments on properties. Textile Research Journal, 54, pp. 827–832, 1984. doi: http://dx.doi. org/10.1177/004051758405401206

[10] Goulart Silva, G., De Souza, D.A., Machado, J.C. & Hourston, D.J., Mechanical and t hermal characterization of native brazilian coir fi ber. Journal of Applied Polymer Science, 76, pp. 1197–1206, 2000. doi:<1197:: AID-APP23>3.0.CO;2-G

[11] Kulkarni, A.G., Satyanarayana, K.G., Sukumaran, K. & Rohatgi, P.K., Mechanical behaviour of coir fi bres under tensile load. Journal of Material Science, 16, pp. 905–914, 1981. doi:

[12] Fluck, R.C & Ahmed, E.M., Measurement by compression test of impact damage to citrus fruits. Journal of Texture Studies, 4, pp. 494–500, 1974. doi: j.1745-4603.1974.tb00859.x

[13] Underhill, S.J.R., Mclauchlan, R.L., Dahler, J.M. & Bertram, J., Flavedo and albedo  changes in ‘Eureka’ lemons caused by static compression and impact loading. Journal of Texture  Studies, 

29, 437–452, 1998. doi:

[14] Seidel, R. Bürig-Polaczek, A., Fleck, C. & Speck, T., Impact resistance of hierarchically structured fruit walls and nut shells in view of biomimetic applications, Proceedings of the 6th Plan Biomechnics Conference, ed. Thibaut, B., French Guyana, ECOFOG: France, pp. 406–411, 2009.