Figure 3.

Mechanical behavior of four representative collagen fibril specimens. The four specimens display differing behavior during the in vitro fracture test, as follows: (a) relatively linear behavior all the way to brittle fracture; (b) two linear regions with a single change of slope before brittle fracture; (c) three linear regions with a double change of slope before brittle fracture; and (d) three linear regions with a double change of slope before a stepwise graceful fracture region. For the sake of clarity, the error bars are shown every five data points. (Thick solid lines) Least-squares fits to relatively linear regions. The initiation of damage is defined as the intersection of the first two fitted lines (indicated by arrows). The fracture point is defined as the point where the stress dropped back to zero (indicated by solid arrowheads). (d) Multiple drops in the graceful fracture region (indicated by open arrowheads), suggesting multiple partial fractures before the complete fracture (solid arrowhead).