The Fracture Research Of Composite Riser Joint With Initial Crack

With increasing of water depth,the traditional steel riser gradually will be difficult to meet the needs of deep oil and gas exploration and development,but the fiber reinforced composite,which has a number of excellent performance,such as the high specific stiffness and specific strength,nice corrosion resistance,fatigue resistance and light-weight etc.,is being applied in the riser system.However,adhesive joints in riser pipes are the most vulnerable part where most failures occur,because singular stress fields exist at the extremes of the interface between the adhesive and the adherend.Generally,the joint’s actual carrying capacity is less than the theoretical carrying capacity.A very important factor is the prevalence of various defects in bonding interface.This paper mainly studies thoroughly such as stress distributions,stress iniensity factor and crack extending through the theoretical analysis and the numerical value calculation:An analytical model is developed based on the first-order laminated anisotropic plate theory to research the adhesive stress distributions.Results obtained from the developed model are compared with finite element models.Good correlations are found.At the base of this,the stress intensity factor of bonded joint with initial crack is derived by combining weight function and slice synthesis methodology.In view of 1500 m water depth of South China Sea,equivalent beam model of riser string is established using ABAQUS,and the dynamic response of riser is obtained under one year storm and 100 years storm operating condition.Extracting the stress field from the dangerous section of whole riser model,is regarded as the boundary conditions of local joint finite element model.On the condition of 1 year storm,setting an initial crack terminating at a biomaterial interface based on extended finite element method(XFEM).By changing the ratio of elasticity modulus and the Poisson’s ratio,we get the trend of crack propagation angle of bonded joint.A finite element model of simplified composite riser joint is established using ABAQUS,and stress distribuctions are calculated under the condition of 100 years storm.In view of condition that crack easily propagates in MCI position,local finite element model which has preset initial cracks is established,then using XFEM module in ABAQUS to predict the crack propagation.