Molding Process And Failure Prediction Research For High Pressure FRP Pipe

High pressure FRP pipe has many advantages, such as high specific strength and stiffness, high pressure resistance, long service life and can be produced in mechanical and automatic way. It has been widely used in oil field, chemical industry and ocean field. It has been paid more and more attention for its excellent mechanical performance and special internal curing process. An urgent problem is how to integrate the winding, curing and mechanical performance analysis of high pressure FRP pipe. For this reason, the following research work has been done:First, the2D finite element model has been made for the internal curing process of high pressure FRP pipe. The heat conduction coefficient matrix has been set with variance method. The finite element code has been developed to simulate the curing process of high FRP pipe. The temperature and curing degree variation along the pipe wall and the effect of fiber volume ratio on the temperature is revealed. The result shows that the finite element model can describe the curing process of high pressure FRP pipe and can be used as the theoretical basis of the curing process.Secondly, the differential geometry is used to derive the non-geodesic trajectory, envelope equation and feeding-eye equation. The APDL parametric design language is used to simulate dynamically the winding process. The data can be used in the two-axis numerical control filament winding machine. The calculation result derived from the plane assumption and differential geometry is compared. The result show that the result from the differential geometry is close to that of geodesic theory and it can make the fiber mechanics best. The structure efficiency of the high pressure FRP pipe is greatly improved.Thirdly, three kinds of test has been done.(1) The longitudinal tensile and compressive strength, longitudinal tensile modulus, transverse tensile and compressive strength, transverse tensile modulus, poisson ratio, in-plane shear strength and modulus is tested for four kinds of laminas of different fiber volume ratio. The regression equation of the mechanical performance is given.(2) The failure pressure is tested for8.8MPa and15.5MPa pipe body.(3) The fiber volume ratio for the whole and each layer is tested for the theoretical analysis and strength prediction of high pressure FRP pipe.Finally, for the uneven distribution of mechanical performance of high FRP pipe, with the Tsai-wu failure criteria, the traditional failure analysis and progressive analysis and APDL parametric language of ANSYS software, the failure strength is simulated for2kinds of pipe bodies and is compared with the tested strength. The result shows that (1) The progressive failure process of the high pressure FRP pipe is from external layer to internal layer. The internal resin rich layer is like elastomer and it can stand large deformation and internal pressure.(2) In the traditional failure analysis, only the failure pressure in the internal layer is taken into account and the residual strength of other failure layers is omitted. The prediction pressure is lower than the tested pressure and the prediction error is5.5%for8.6MPa pipe and6.5%for15.5MPa pipe. The traditional prediction analysis is conservative.(3) The residual strength is taken into account in the progressive prediction analysis. The prediction pressure is higher than the tested pressure and the prediction error is2.9%for8.6MPa pipe and2.0%for15.5MPa pipe. The progressive prediction analysis is more reasonable.(4) The final laminate failure of the high pressure FRP pipe is not caused by the fiber fracture instead of the resin failure. This means that the resin rich layer of the internal surface by the internal curing process of high pressure FRP pipe improves the load capacity greatly.This research work provides not only the theoretical evidence and testing basis for the winding, curing and the design and analysis of mechanical performance of high pressure FRP pipe, but also the precious information for the design and manufacturing of other glass fiber/epoxy composites.