Graphical Solution of thermal Stresses by Welding (Reprt III)

On the removal of distortion in welded thin plate structures

Abstract

It is usually adopted to spot heat the warped plate by oxyacetylene flame followed by subsequent water cooltng, in order to remove distoations in welded thin structures. The purpose of this report is to explain the theoretical foundations of this practice, and at the same time determine the best condition of heating operations.
The experiments were made about the models shown in Fig. 1, and test results analysed theoretically. The thermal stress due to temperature changes were elastically calculated at first, and then corrected by the graphical method considering plastic yieldings around the locally heated part. Using tnus determined stress distributions, the displacement a could be calculated during heating and cooling by trial method taking the mininmm strain energy condition, accordingly the amounts of removable distortions were determined. In those calculations, the mean values of mechanical constants (Young's modulus, yielding stress, coefficient of thermal expansion) were adopted for each small temperature intervals to derive the accurate results. As in Figs. 4 and 5, the good coincidences were indicated between the test results and calculated values. Einally, the following conditions were theoretically determined to be most recomendable:
heating temperature 500-550°C
radius of heating 20-25mm
pitch of heated spots 57-70mm