PSI - Issue 24

Raffaella Sesana et al. / Procedia Structural Integrity 24 (2019) 829–836 R. Sesana et al. / Structural Integrity Procedia 00 (2019) 000–000

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Failure stresses s r were calculated for each specimen and average values are reported in Table 3. In particular, s af P is the maximum stress for sample in P direction, average on all the samples, s af M the maximum stress for sample in M direction, average on all the samples, and s a the average stress calculated on the variety . These values are consistent with Dong and Davies (2012). 4.2. ANOVA The factors affecting the failure stress σ r were investigated by means of ANOVA analysis. The influence of the following parameters was investigated: nut variety (keeping the cut direction constant), and cut direction (keeping the variety constant). In the first case (influence of variety) it results that for both P and M specimens the nut variety is not influent on the failure stress value, this is true with 95% confidence. In the second case (influence of cut direction), it results that for all the three nut varieties, cut direction affects the failure stress; this is true with 95% confidence. 5. Conclusion An experimental testing campaign was run on three varieties of macadamia nutshell to investigate the influence of variety and specimen cut direction on mechanical properties. The investigated varieties are A16, A4 and 816. According to specimen shape, the analytical model of curved beam was applied to estimate stresses in the specimens. Three points bending test resulted to be a reliable test for investigating mechanical behavior of the nutshell. From the experimental campaign it resulted that macadamia nutshell has relevant mechanical properties, in particular the stress to failure can reach 100 MPa for the investigated varieties. Mechanical properties of shells are related to their internal structure and, in particular, to the secondary fibers. Their influence is related to their extension and orientation in the point of maximum stress in the specimen. The accuracy in specimen preparation strongly affects result reliability. The macadamia nut variety is not influencing the resistance properties of the shell for the investigated varieties. The most affecting parameters resulted to be the specimen cut direction. Approximating the shell to an ideal arch is reliable for stress calculation but not for density evaluation. References Braga, G. C., Couto, S. M., Hara, T., Neto, J. T. P. A., 1998. Mechanical behaviour of macadamia nut under compression loading. Journal of Agricultural Engineering Research 72(3), 239–245. Bonisoli, E., Delprete, C., Sesana, R., Tamburro, A., Tornincasa, S., 2015. Testing and simulation of the three points bending anisotropic behaviour of hazelnut shells. Biosystems Engineering 129, 134–141. Cholake, ST., Rajarao, R., Henderson, P., Rajagopal, RR., Sahajwalla, V., 2017. Composite panels obtained from automotive waste plastics and agricultural macadamia shell waste. Journal of Cleaner Production 151, 163-171. Dong, C., Davies, IJ., 2012. Flexural properties of macadamia nutshell particle reinforced polyester composites. Composites Part B: Engineering 43 (7), 2751-2756. Dong, C., Davies, I. J., Fornari Jr, C. C. M., Scaffaro, R., 2017. Mechanical properties of Macadamia nutshell powder and PLA bio-composites. Australian Journal of Mechanical Engineering 15(3), 150–156. Pilkey, W. D., 2008, “Formulas for Stress, Strain, and Structural Matrices”. Wiley, USA, Chapter 16. Sesana, R., Delprete, C., 2014. Mechanical characterization of kernel and shell of hazelnuts: Proposal of an experimental procedure. Journal of Food Engineering 124, 28–34. Vock, N. T., 1998, “Macadamia variety identifier”, Agrilink Series. Queensland Department of Primary Industries, AU, ISBN 0724267972. Wang, C. H., Mai, Y.W., 1995. Deformation and fracture of Macadamia nuts. Journal of Fracture 69, 67–85. Wallace, H. M., Walton, D. A., 2012. Genetic and postharvest factors affecting macadamia kernel quality. African Journal of Agricultural Research 7(16), 2490–2495.