Mechanical properties of matrices and fibre reinforcements

The mechanical properties of both polymeric and hbrous components in FRP strengthening systems play an essential role in determining the load transfer mechanism, and thus the initiation and evolution of the critical stress variants responsible for controlling the failure pattern and its location within the composite joint, as detailed in succeeding sections of this chapter. 

The lap-shear stress distribution, the failure pattern and ultimately the bond strength of FRP joints are also functions of the mechanical properties of the FRP reinforcing fibres. This behavioural dependency is depicted in Fig. 10.3 where lap-shear stress distributions along the bondlength for two identical double-strap CFRP/steel specimens, with different elastic moduli of their reinforcing CF (carbon fibres), are presented. 

In FRP composite strengthening for civil engineering applications, two generally accepted material models are utilized in the mechanical characterization and stress analysis of FRP adhesive joints, viz. microstmctural and macrostructural material models. Microstmctural models take into account FRP material heterogeneity, and accordingly make use of the fibre and matrix properties, individually, in analysing FRP behaviour. On the 

2 Effect of adhesive ductility on bond strength for identical double-strap CFRP/steel plate specimens at different exposure temperatures (Al-Shawaf, 2010). 

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