Thermomechanical qualification of composite pipes under different laws of loading

Reinforced plastics are complex, heterogenous and anisotropic materials that need high performance means of design and control to certify their reliability and the safety of the environment in which they are used. Since a few years, several investigations have been realized to determine the instantaneous behaviour of pipes tested under biaxial stresses. It has been shown that the optimum winding angle for a cylindrical structure varied in function of the loading mode. For example, the optimum angle in the case of internal pressure test is 550. Such tests have made it possible to find the fracture mechanisms and to improve the design of tubular structures, the end of life criteria the most often taken were weeping. After a short description of experimental plants designed in our laboratory to measure the behaviour of industrial pipes tested under different laws of pressure, we shall discuss about the scattering of behaviour in function of the composite structure, the physical meaning of the end of life criteria and the difficulty to forecast these criteria with the existing softwares of modelization