PSI - Issue 14

Ramesh Babu Adusumalli et al. / Procedia Structural Integrity 14 (2019) 150–157 R.B. Adusumalli / Structural Integrity Procedia 00 (2018) 000 – 000

157

of crystalline alpha keratin coils embedded in amorphous keratin matrix. These helical coils can be elongated easily without using excessive force as the helical coils can extend greatly and become a random coil without losing their structural integrity when tensile stress is applied. But during the nanoindentation test, these helical coils require large amount of force for compression as the spaces in between the helical coils are filled up with amorphous keratin matrix. There is no question of underestimation of fibre longitudinal indentation modulus due to the indenter tip geometry as explained in Gindl et al. (2008), because here microfibrils are made of helical protein filaments and are not oriented in fibre direction if small depths are considered. As shown in Table 1, the bleached pulp fibres (MFA is 15-25 0 ) also showed higher indentation modulus values compared to tensile modulus values because microfibril orientation has been partially destroyed by bleaching with lot of cell wall defects. Infact both indentation modulus and tensile modulus values of pulp were lower than wood values (Lehringer et al. 2011), but decrease is significant in case of tensile modulus because of numerous defects in the cell wall structure. During nanoindentation, normally defect free zone is selected which would give higher modulus unlike the whole fibre length (2 mm) is subjected to tensile testing which obviously considers more defects thereby resulting in lower value of tensile modulus. Adusumalli, RB., Reifferscheid, M., Roeder, T., Weber, H., Sixta, H., Gindl, W., 2006. Mechanical Properties of Regenerated Cellulose Fibres for Composites. Macromolecular symposia 244, 119 – 125. Adusumalli, RB., Keckes, J., Martinschitz, K., Boesecke, P., Roeder, T., Weber, H., Sixta, H., Gindl, W., 2009. Comparison of molecular orientation and mechanical properties of lyocell fibre tow and staple fibres. Cellulose 16(5), 765 – 772. Adusumalli, RB., Mook, WM., Passas, R., Schwaller, P., Michler, J., 2010. Nanoindentation of single pulp fibre cell walls. Journal of Materials Science 45, 2558 – 2563. Agarwal, BD., Broutman, LJ., Chandrashekhara, K., 2006. “ Analysis and Performance of Fibre Composites ” . John Wiley and Sons Inc, pp.21. Bencom-Cisneros, JA., Tajeda-Ochoa, A., Garcia-Estrada, JA., Herrera-Ramirez, CA., Hurtado-Macias, A., Martinez-Sanchez, R., Herrera-Ramirez, JM., 2012. Characterization of Kevlar-29 fibres by tensile tests and nanoindentation. Journal of Alloy and Compounds 536, S456 – S459. Bourmaud, A., Baley, C., 2012. Nanoindentation contribution to mechanical characterization of vegetal fibres. Composites:Part B 43, 2861-2866. Buksnowitz, C., Adusumalli, RB., Pahler, A., Sixta, H., Gindl, W., 2010. Acoustical properties of Lyocell, hemp, and flax composites. Journal of Reinforced Plastics and Composites 29(20), 3149-3154. Chawla, KK., 1998. “ Fibrous Materials ” . Cambridge University Press, New York, pp. 256. Chawla, KK., 2010. “ Composite Materials: Science and Engineering ” . Second edition, Springer-Verlag, Newyork, pp. 13. Gindl, W., Konnerth, J., Schoeberl, T., 2006. Nanoindentation of regenerated cellulose fibres. Cellulose 13, 1 – 7. Gindl, W., Reifferscheid, M., Adusumalli, RB., Roeder, T., Weber, H., Sixta, H., Schöberl , T., 2008. Anisotropy of the modulus of elasticity in regenerated cellulose fibres related to molecular orientation. Polymer 49, 792 – 799. Lehringer, C., Koch, G., Adusumalli, RB., Mook, W., Richter, K., Militz, H., 2011. Effect of Physisporinus vitreus on wood properties of Norway spruce. Part 1: Aspects of delignification and surface hardness. Holzforschung; 65(5), 711-719. Mishra, S., Kunchi, C., Venkateshan KC., Gundakaram, RC., Adusumalli, RB., 2016. Nanoindentation and Tensile testing of Human Hair Fibres. Journal of Materials Science 51(22), 10191 – 10204. Revol, BP., Thomassey, M., Ruch, F., Nardin, M., 2016. Influence of the sample number for the prediction of the tensile strength of high tenacity viscose fibres using a two parameters Weibull distribution. Cellulose 23, 2701 – 2713. Samanta, A., Bhattacharya, M., Dalui, S., Acharya, M., Das, PS., Chanda, DK., Acharya, SD., Sivaraman, SK., Nath, S., Mandal, AK., Ghosh, J., Mukhopadhyay, AK., 2016. Nanomechanical responses of human hair. Journal of Mechanical Behavior of Biomedical Materials 56, 229 – 248. Varughese, Sunil, Kiran, MSRN., Upadrasta, Ramamurty, Desiraju Angew, Gautam. R., 2013. Nanoindentation in Crystal Engineering: Quantifying Mechanical Properties of Molecular Crystals. Angewandte Chemie 52, 2701 – 2712. References