Fig. 2

Evaluation of FOS orientation. (a, b) FOS placement of a prototype indicated by red lines. (c, d) Distributed strain recording from a horizontally or vertically oriented FOS when penetrating 1.2 mm-diameter metal wire at 1 mm/sec into the center of a pot filled with glass beads. (e, f) Stress-strain scatter plots of (c) and (d), respectively. The fit for linear regression is annotated in the respective panel. For (f), the fit only applies to the linear range (< 1 MPa)