3.5.3. Tearing Tests

The tearing test is classified as a type III mode of fracture mechanics (out-of-plane fracturing test) and allows the fracture propagation on the plane to be studied by applying an out-of-plane shear [83]. Two types of tearing tests were performed on treated and untreated tissues: Elmendorf and trouser tearing tests. The differences between these tests were mainly in the test speed; the Elmendorf apparatus is composed of a swinging pendulum that was released, causing a very fast propagation of the crack, while the trouser test was a test with a controlled strain rate.

In Figure 11a, the trouser tear propagation force is shown, which can be defined as the force required to propagate the crack. TP and TW samples showed similar values, denoting that, in this case, the application technique did not affect the measured property. Instead, TA and TC showed, respectively, lower and higher values with respect to TP and TW. Regarding the analysis direction in all samples, it was observed that the crack required more force to propagate in CD compared to MD, conversely to the behaviour observed in the tensile test. This behaviour agreed with a partially oriented fibre structure where a tear can easily propagate parallel to the fibres with respect to the perpendicular direction.

**Figure 11.** Tear propagation force (**a**) measured through trouser test and tear propagation resistance (**b**) measured with Elmendorf pendulum. Significance of standard deviation was investigated with a Tukey HSD post hoc test performed on 4 different specimens for Elmendorf test and on 5 different specimens for tear propagation test. On the top of each column, a letter was reported. Means that were identified as not significantly different were grouped under the same letter.

Elmendorf tearing test results reported in Figure 11b showed a trend similar to the trouser test but with some differences. The obtained results were all higher compared to the respective values observed in the trouser test due to the higher test speed. Differences between TP and TW were shown, with an increment in tear resistance caused by the application technique, but in these two samples, the difference between MD and CD was no longer visible. Conversely, in TA and TC, higher values in CD were observed compared to MD, maintaining the same trend observed in the trouser test with propagation tear resistance values of TA and TC, respectively, lower and higher with respect to TP.

Analysis of variance of both trouser and Elmendorf tearing tests showed the same grouping of means, evidencing a significant difference between TC and TA tissues. In particular, TC showed the highest tearing resistance values in all tests and directions, while TA showed the lowest ones.
