Measuring stresses in FRP composite bonded joints

In order to maintain equilibrium of the FED, the change in FRP laminate tensile force (AF) between any two adjacent ERSG positions (e g. SG4 and SGs) due to a difference in their corresponding strain readings ( 4 - 5) 

70 Double-strap FRP composite ERSG-instrumented joint depicting the force equilibrium for a FBD between the positions of two consecutive gauges. 

Non-contact strain measuring methods are generally based on optical principles. The principal methods addressed in the literature include MI or SI (moire or speckle interferometry), and DIG (digital image correlation). Amongst their advantages, whole-field, non-contact or remote measurement 

During the last three decades, MI/SI techniques have been implemented in measuring the in-plane surface deformation of the overlap region of FRP adhesively bonded joint specimens (Lilleheden, 1994 Post, 1993 Ruiz et al., 2006, 2011 Schumacher and Hack, 2008 Tsai and Morton, 1995 Tsai 

It is worth mentioning that the lap-shear stress term of equation [10.5], when incrementally calculated, yields an identical form to that of equation [10.3]. In addition, all the simplifying assumptions stated previously for the latter equation are applicable for equation [10.5], as well. 

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