Efficiency of mechanical joint is largely dependent on quality of machined holes

Efficiency of mechanical joint is largely dependent on quality of machined holes. Due to their anisotropy and non-homogeneity, FRP cause some problems in drilling such as fibre breakage, matrix cracking, fibre/matrix debonding, fibre pull-out, fuzzing, thermal degradation, spalling and delamination. Among the defects causes by drilling, delamination is the most critical due to the fact delamination is responsible for the rejection of approximately 60% of the components produced in the aircraft industry. Delamination can result in lowering of fatigue strength (acts as a point of crack initiation), leads to poor assembly tolerances and can be determined to the material durability by reducing structural reliability of the material resulting in lasting performance worsening. Two delamination mechanisms associated with drilling FRP are known as peel-up at the entrance and push-out at the drill exit (Khashaba 2012).