ratcheting

Ratcheting describes two related ideas in engineering and science. In mechanism design, a ratchet is a device that converts motion in one direction into a unidirectional drive. In materials science and economics, ratcheting denotes a progressive, irreversible change that accumulates under cyclic or staged inputs.

A typical ratchet consists of a toothed wheel and a pawl. The wheel turns freely in the allowed direction; when it tries to rotate the other way, the pawl catches on a tooth and stops it. Variants include self-locking ratchets and designs with disengageable clutches. Ratchets appear in many tools and machines, such as wrenches, clocks, winches, and line reels.

Applications include hand wrenches, hoists, and winches where unidirectional drive provides torque transfer or safety. Some systems use multiple pawls or springs to share load or control backlash.

In materials science, ratcheting refers to the gradual buildup of plastic strain under cyclic loading, especially with nonzero mean stress. Repeated loading can accumulate permanent deformation even if the alternating stress remains constant, affecting fatigue life and precision. Designers mitigate ratcheting by controlling mean stress and choosing materials with favorable cyclic response.

In economics and policy, the ratchet effect describes irreversible changes that are difficult to reverse, such as rising costs, standards, or commitments once established. The concept is used to analyze climate pledges, wage agreements, and regulatory frameworks that tend to tighten over time.