Solutions to some important issues in strain gage based determination of stress intensity factors

Abstract

In order to determine the stress intensity factor(SIF) of cracked components using strain gages, some of the important issues needed to be answered were, number of strain gages and their correct placements ensuring accurate determination of SIFs. This article reports the development of strain gage techniques for determination of SIFs and how these important issues have been addressed by the authors following the fundamental development of single strain gage technique by Dally and Sanford (DS) [1] for determination of mode I SIF (KI). Only recently, a procedure was proposed by the authors and co-worker [2] for determination of valid strain gage location where a single strain gage could be placed following DS technique ensuring accurate mode I SIF. Authors with other co-worker also extended the DS technique to orthotropic materials [3]. Similarly based on the Dally Berger [4] technique the authors developed a procedure [5] for accurate determination of mixed mode SIFs using six strain gages placed at valid radial locations. This has also been extended [6] to orthotropic materials for accurate determination of mixed mode SIFS. Through these developments, a long pending problem of determination of valid radial locations for placing the strain gages have been resolved thereby enhancing the ease of applying the DS and DB techniques for accurate determination of mode I and mixed mode SIFs. In addition a single strain gage technique in line with DS technique and a multiple strain gage technique in line with DB technique have also been proposed for orthotropic composites.