The influence of rapid thermal transients on elastic-plastic ratchetting

Abstract

The ‘Bree diagram’ allows a rapid design assessment of the likelihood of incremental plastic deformation. The diagram was originally developed for plate or beam components subjected to steady mechanical and quasi-steady cyclic thermal loadings. Here, a theoretical investigation shows that a cycle of rapid cooling and quasi-steady heating reduces the combinations of load which do not give rise to ratchetting. This effect approaches an asymptote for large Biot numbers and small Fourier numbers, and is more significant for mechanical loads less than about 30% of yield. Revised interaction diagrams are presented for two load cases of interest and for a worst-case combination of Biot and Fourier numbers. If equal thermal transients are applied to both outer surfaces of a plate, then it is shown that a critical thickness can be found below which ratchetting need not be expected for temperature transients of practical magnitude. This is presented as a function of mechanical load and Fourier number.