New formulas for calculating mode II fracture energy of several typologies of GRP pipes under impact

The authors suggest a simple monomial formula to determine the delamination starting energy U0 under impact in GRP pipes with sand filled layer. By means of analytical procedures, deducted from the Mechanically Contaminated Layer Theory, a new equation in mode II of fracture, unique for all types and different manufacturers is developed.The shape of this equation adjusts in a 98.96% of the observed law and mainly depends on the square of the height of the tube and its resistance to internal hydraulic pressure, achieving numerical errors, using a general theoretical coefficient, of less than 10% for pipes of very different kinds, that can be improved using empirical coefficients customized for each manufacturer.Thus, it facilitates technicians with a practical design tool against the invisible effects of a blow and warrants seriously rethinking the current design criteria that does not take into account the brittleness of an impact.