An Extended Shakedown Theory for Structures That Suffer Cyclic Thermal Loading, Part 1: Theory

The paper describes an extension of classical shakedown theory for structural problems involving constant mechanical loads and cyclic variations in temperature. The objective of the theory is to provide a simple means of distinguishing between circumstances where thermal cycling can cause structural ratchetting for small or zero mechanical loads from those where very substantial thermal stresses can occur with no danger of ratchetting. This distinction is of particular importance in the design of Liquid Metal Fast Breeder Reactors and current design codes do not address this problem directly. An extended definition of material shakedown is described that provides a conservative theory, taking into account cyclic strain hardening. Some simple experiments on a two-bar structure demonstrates the relevance of the theory to observed structural behavior.