Experimental Studies on Welding Stresses (4 th Report)

Effect of Peening on the Suppression and Relaxation of Welding Stresses

Abstract

In the present report, the Author studied experimentally the influences of peening on the processes of relaxation and the processes of generation of restraint stresses using a restraint frame apparatus. The same experiments were also made to examine the influences of peening on residual stresses.
The main conclusions obtained from the above results are as follows :
(1) Although the decrease of welding stresses by peening is remarkable at early stages, it becomes gradually saturated because peened specimens workharden. In other words the relation between restraint stress and log. of peening time is linear.
(2) Also a linear relation exists between log. of relaxation rate of stresses and peening pressure.
(3) There are ranges of a certain optimum temperature in the influence of hot peening on suppression and relaxation of stresses, that is 200-300°C.
(4) The effect of peening on base metals is about the same in its extent as that on deposit metal, but peening on a heat affected zone is not so effective as on the others.
(5) The tip areas of peening tools have scarcely any influence on the stress relief.
(6) Although the growth of residual stress caused by the approach of the heat source can not be suppressed by peening, stresses that grow as the heat source gets kept away can be considerably suppressed by giving a suitable hot peening.