Figure 1
From: Biaxial stress controlled three-dimensional helical cracks
Intact and helically cracked spindle knots before and after calcination. (a) Optical image of periodic spindle knots wrapped around a uniform smooth glass microfiber. Inset of scanning electron microscopy image of a spindle knot showing the intact smooth surface. (b) Screwed microcracks formed on the spindle knots after calcination. (c) A typical helically cracked spindle knot with seven coils.(d, e) Magnified views of the helical crack showing the brittle fracture and completely interfacial delamination between the core and shell.
