PSI - Issue 28

Shirsha Bose et al. / Procedia Structural Integrity 28 (2020) 843–849 S. Bose et. al/ Structural Integrity Procedia 00 (2019) 000–000

846

4

3. Results and Discussions 3.1. Stress-strain Curves

The stress-strain graphs obtained for Col D and Col A specimens are plotted in Figs. 3a and 3b, respectively, with error bars representing the standard deviation. The tensile strength dropped to more than 95% for Col A films, which was compensated by an increase in strain-at-failure by about 1600% as compared to Col D . Col D exhibited a linear deformation with a transition to non-linearity just before failure while the Col A depicted non-linear deformation with extensive plasticity. Thus, apparently, in-air collagen showed brittle failure but in-aqua it had a ductile one.

Fig. 3. Stress-strain cures for in-air (a) and in-aqua (b) test environment.

The drastic difference in the mechanical properties of Col D and Col A specimens are reported in Table 2 along with unnotched specimens. There was a reduction in the load-bearing capacity for SENT specimens under both environmental conditions as opposed to unnotched specimens. The strain-at-failure for unnotched and SENT Col A was comparable while SENT Col D specimens revealed a brittle failure at a significantly lower strain than its unnotched counterpart. The fracture energy was calculated for SENT Col D and Col A specimens (Table 2), with a drop of 40% in its level observed for Col A specimens. In-aqua condition acted as a plasticizing agent, decreasing the mechanical properties while dramatically increasing the ductility (Yuan and Verma, 2006; Bose et al., 2020a).

Table 2. Mechanical parameters obtained from tensile behaviour under different environmental conditions.

Specimen type

Ultimate tensile strength (UTS) (MPa)

Strain at failure (%)

Fracture energy (MJ/mm 3 )

Col D (unnotched) Col A (unnotched)

75.7 ± 15.7 2.74 ± 1.00

23.5 ± 2.5 55.9 ± 2.00 3.12 ± 0.94 50.94 ± 1.5

- -

Col D (SENT) Col A (SENT)

19.5 3.85 0.96 0.17

41.5 ± 20.1 24.5 ± 2.9