Measurement of Transient Strain during Welding by Grid Patterns

Abstract

The present study proposes a measurement of transient welding strains in areas near weld. In the measurement technique, grid patterns previously photo-etched on surface of a plate are photographed progressively during welding; after welding, each grid distance at every moment is observed with the photographic film using micro-photometer, from which total strain is determined. Experiments are conducted to examine the accuracy of the measurement and the mechanism of radial and circumferential strains in aluminum alloy thin plate heated by gas tungsten arc. Moreover, the plastically deformed zone in the plate is sized from the two-dimensional total strain values by a mathematical equation based on the theory of elasticity and plasticity. The main results are as follows.
The photographic recording method reveals precisely the total strain distribution which shows the individual change according to the plastic deformation occurring around the molten zone and the cooling effect of shielding gas as well as the thermal expansion of the plate. The size of plastic zone calculated from the total strain values after heating is reasonably close to that experimentally observed by stress relaxation. The size spreads at early stage of the heating with additional deformation in the thickness direction and increases with increasing heat input.