Concept
Torsion constant — where it appears
The section property that resists twist, computed from an enclosed area for a closed section and from wall thickness cubed for an open one.
Named by 2 essays across one field — each of them below, with the objects they name alongside it.
The moment that will not lie flat
A plane cut exposes three actions. A real cut exposes six, and the fourth of them behaves unlike the others — torsion is resisted by a loop of shear, and one slit down the length of a tube destroys it.
The internal force with no diagram
A cut through a member reveals four things, and this collection has drawn diagrams for three of them. The fourth is a torque, it obeys exactly the same rules, and whether it exists at all can depend on a decision the designer is free to make.
Named alongside it
The objects these essays reach for when they reach for this one.
Shear centreShear flowTorsionWarpingCompatibility torsionHollow sectionInternal forcesOpen sectionStiffnessStress resultant