Regular microhelics on a heterogenous spindle knot are obtained by controlled biaxial stresses in three dimensions. The spindle knot has a tough core and a brittle shell, resulting in biaxial stresses that arise from a thermal expansion mismatch during a heating process. Surface cleavage and interface delamination are harmonized due to the special spindle geometry and cooperate to 3D helical crack. This study not only widens our understanding of the cracking phenomena, but also sheds light on the control and design of regular cracks in arbitrary dimensions. It holds promise for applications in eliminating or controlling cracks for manufacturing process, especially at micro/nanosales, which domains are difficult to be generated by routine methods.
- Li Wang
- Xiang-Ying Ji
- Lei Jiang
