Measurement of residual stress using linearly integrated GMR sensor arrays

Tubular-type transmission towers have several advantages, but could be compromised if welding defects from the construction process are not found during deployment. This research derived an equation that illustrates how a change in stress accompanied with mechanical deformation triggered a change in distribution of magnetic flux density. Furthermore, it verified experimentally that a change in distribution of magnetic flux density occurred due to a change in stress at the welding zone. Using this principle, this research proposes a system to measure residual stress occurred in the welding zone of tubular-type transmission tower. The ultrasound examination results were compared and the result showed that ultrasound signals revealed defects in a place where sudden distribution of magnetic flux density was presented. However, when a number of welding defects occurred across the large area, the distribution of magnetic flux density may not change due to the alleviating effect of the stress concentration.