In this report, the problems of generation processes of welding residual stresses were studied with experimental techniques using the special resistance wire strain gauges usable up to 400°C, directly attached on the samples.
The apparent strains were continuously recorded an automatic recorder. The inherent strains were calculated by subtracting rectified values ascribed to the temperatures characteristic of strain gauges and the thermal expansion of the samples from apparent strains.
The experimental results are summarized as follows.
As to the generation processes of stress parallel to weld lines in the parts adjacent to weld lines, compressive stress first grows with the approach of the welding heat source, and falls off swiftly when the heat source is kept away, tensile stress growing rapidly instead.
This tendency of stress changes when welding becomes violent with the increase of an input heat.
The behaviour of stresses during the welding and cooling at the points farther away from the welding lines is quite opposite to that in the neighbourhood of the welding lines.
Close to the time when weld starts or finishes, the weld is discontinuous, and the generation processes of stresses perpendicular to the weld lines are remarkably different from those at the time when weld reaches its stationary state.
In general, although the generation processes of stresses are not essentially influenced by preheating all over the specimens, the curves of stress behaviour become more or less slow and the residual stresses slacken.
The local preheating, however, of the groove tend to cause a great change in stress and enlarge the residual stresses.
View full abstract