2002 Volume 20 Issue 4 Pages 531-538
The authors have been trying to apply the laser speckle method in the strain measurement at a high temperature such as in the case of welding process. We already reported that in-situ strain measurement over 1000°C is possible and some phase-transformation during cooling of a weld metal has been successfully measured, for example. However, strong light emission from the welding arc restricted us to measurements from the bottom surface. In the present report, we first extended the period of measurement from the bottom surface to include the hottest thermal cycle when the metal at the measuring position is molten. By using optical filters to improve the S/N ratio of laser speckle pattern against arc light and using signal processing to eliminate fluctuation due to thermal convection, we could measure strain behavior on the top surface with reasonable accuracy. With these improvements, the instrument has become more adapted to actual welding process.
