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

153

Fig. 2. Single fibre testing set-up. Direct gripping (left) is used for textile fibres and paper frame set-up (right) is used for technical fibres. Note the pretension weight used to remove the crimp before testing in direct gripping method.

Fig. 3. Stress-strain plots of glass, flax, lyocell, viscose and hair fibres obtained from single fibre tensile testing.

3. Nanoindentation of single fibre cross sections to measure modulus Except glass fibre all are anisotropic fibres, so nanomechanical analysis on fibre cross section was carried out to obtain a relationship between nanoindentation modulus and tensile modulus. Sample preparation was successfully developed using agar epoxy resin in which bunch of fibres are embedded vertically as shown in Fig. 4. (b). The cured epoxy blocks were smoothed using microtome (Leica RM2255) and finally with diamond knife to obtain smooth and transparent surface of fibre cross sections as shown in Fig. 1. (a) and (b) and also in Fig. 5. Indentations tests were performed using berkovitch diamond indenter and modulus was determined from the unloading portion of the load depth plot. Initial slope of the unloading curve (S) and indenter contact area (A) are used to measure the indentation modulus as explained in Mishra et al. (2016). On average 4-5 indents were placed on each fibre cross section as shown in Fig. 1. (a) and (b) and also in Fig. 5. Indents were placed in force controlled mode with peak load of 240 µN, the loading and unloading speed was 100 µN /s and the holding time at peak load was 15s. These parameters were varied slightly for different fibres depending on fibre roughness and diameter. Load was increased with increase in roughness and load was decreased with decrease in diameter to avoid the influence of surrounding embedding material.