Study Of Mechanical Behavior And Process-induced Residual Stress Of Composite Pipes

Fiber reinforced composite pipe is widely used in aerospace,marine engineering,automobile,chemical industry fields due to its thermal stability,oxidation resistance,corrosion resistance and designability.Composite marine risers is an essential equipment in marine engineering,which is used to connect the working platform and the seabed wellhead.During the process of composite pipes,residual stress will be generated due to the mismatch of thermal expansion coefficients between fibers and matrix materials,which will seriously affect the bearing capacity.In this dissertation,the influence of composite pipe forming process on its bearing capacity is studied.Firstly,the process-mechanics model of thermoset and thermoplastic composite pipes are established to obtain the distributions of cure of degree,crystallinity,temperature and residual stress in the forming process;Then,based on the obtained residual stress,the progressive damage analyses of thermoset and thermoplastic composite pipe with and without liner are carried out.Finally,the damage of T700/PPS composite pipe under different loads is analyzed.the rationality of manufacture marine riser with thermoplastic composites is verified.The main contents of this article are as follows:(1)Residual stress analysis of thermoset composite pipes: Based on the curing kinetic equation of 3501-6 epoxy resin and its constitutive model in process,the thermal-curingmechanical coupling analysis model of thermoset resin matrix composites is established.The effects of different constitutive models on the residual stress are compared and analyzed.The residual stress in the process of thermoset composites pipe is obtained.(2)Residual stress analysis of thermoplastic composite pipes: The thermal-crystallizationmechanical coupling analysis model in the process of T700/PPS Composites was established.The residual stress and deformation of thermoplastic composites were predicted.Non-isothermal Differential Scanning Calorimetry test and hot pressing test of T700/PPS composites were carried out.The accuracy of the numerical model was verified by measuring the forming deformation of the specimen.(3)Study on bearing capacity of composite pipe: Based on Tsai-Hill criterion,maximum distortion energy theory and Chang-Lessard model,a progressive damage model of composite pipe with residual stress is established.The leakage pressure of composite pipeline under internal pressure load is obtained.The effects of transportation pressure,external pressure and axial load on the damage of composite pipe are analyzed.The results show that the difference between the transportation pressure and the external pressure is the key factor leading to the damage of composite pipe.