Growth monitoring of internal surface crack by strain measurement of external surface. Application of multiple strain measurement method

The cracks detected by in-service inspection are not always removed when they are not hazardous according to fitness-for-service evaluations. In such cases, it is important to monitor the growth of these cracks in order to assess the validity of their integrity assessment. In previous study, a monitoring method using strain gage was proposed and its validity was shown by performing finite element analyses and experiments. In this study, this method was extended for estimating not only crack depth but also surface length. By using two strain gages, it was possible to identify the both size. Furthermore, by using several gages and averaging the estimated sizes from the gages, the accuracy of the estimation could be improved. By considering weights in the averaging, further improvement of the accuracy was achieved. (author)