Fig. 5: Data obtained from the bending tests on Ea. and Ta. spicules.
a The wedge is used to apply a force \(-F{\hat{{\bf{e}}}}_{2}\). The displacement of the stage is \(-{w}_{{\rm{s}}}{\hat{{\bf{e}}}}_{2}\) and the corresponding displacement of the spicule’s cross-section at x1 = L∕2 is \(-{w}_{0}{\hat{{\bf{e}}}}_{2}\). The stage is denoted by a black dot. The glue (shown in green) prevents the ends of the spicule from rotating or moving relative to the plate to which it is attached. b After the specimen has failed completely, it resembles two cantilevers. c The F-w0 response of a representative Ea. spicule. d The F-w0 response of a representative Ta. spicule. The F-w0 data obtained during loading and unloading are shown as dark gray points and light gray points, respectively. Crack initiation (i.e., pop-in) is marked as a red square and has a force and displacement of Fc and wc. The insets in c and d show a magnified view of the F-w0 response leading up to pop-in and the drop in force during pop-in, ΔFc. The point of complete failure is marked with a green square and has a force and displacement of Ff and wf. The blue line with slope 1∕Cf is the line that passes through the origin and the point (wf, Ff). The shaded region marked UF in c and d is the area enclosed between the F-w0 data and this line.
