Preparation And Finite Element Analysis Of Composite LNG Vehicle Cylinders

Composite Liquefied Natural Gas(LNG)cylinders are pressure vessels used to store high-pressure gas.They are key energy storage components of natural gas vehicles and other transportation vehicles.Compared with metal gas cylinders,LNG cylinders are relatively lightweight and have higher specific strength and stiffness,and better service life and fatigue resistance.Therefore,they are widely applied in other industrial fields apart from the automobile industry.LNG cylinders develop slowly in China relative to that in developed countries.The domestic vehicle gas cylinders are either imported or their most important raw material carbon fiber needs to be imported,which leads to the high cost of products and limits the development of LNG vehicle cylinders industry.With the rapid development of the carbon fiber industry and the continuous progress of composite molding technology in China,the mechanical properties and stability of domestic carbon fiber have been greatly improved.Therefore,studying the molding process of vehicle LNG cylinders by using domestic carbon fiber,mastering the key technologies of gas cylinder molding,and realizing the substitution of LNG cylinders by domestic production is of great practical significance for the development of Chinese LNG cylinders industry.To solve this problem,in this paper,the forming process and preparation of gas cylinders were studied by using T700-grade carbon fiber as the raw material of gas cylinder and steel inner liner as the winding core mold.The structure of LNG cylinders was designed and optimized through finite element software.Besides,failure mode analysis and self-tightening pressure optimization were conducted.Technical support was provided for the localization replacement of LNG cylinders.Specific research contents were as follows:(1)Stress analysis of composite LNG vehicle cylinders.First of all,the shape and size of the cylinders were determined by designing their structural parameters.Then,a three-dimensional model of the gas cylinder was established by using the commercial finite element software Abaqus to explore the properties of the material model and the mechanical properties of the material.The ultimate bearing stress of the gas cylinder under various working conditions was simulated through grid division and boundary conditions setting,and the stress distribution of the inner liner and the fiber winding layer was obtained to predict the ultimate bearing capacity of the LNG cylinder.(2)The progressive damage of composite materials.According to the basic mechanics of composites,the progressive failure process of composites was analyzed by selecting the 3D Hashin failure criterion and Camanho degradation scheme.The results showed that the failure of the composite cylinder was not instantaneous,but a gradual process from matrix cracking to fiber cracking.The single layer and local failure of the composite material would not immediately cause the whole failure of the cylinder.Based on the progressive damage analysis,the maximum bursting pressure of the cylinder was predicted to be 58 MPa.(3)The effect of self-tightening pressure on the performance of LNG cylinders.The necessity of self-tightening treatment for the cylinder preparation was demonstrated by comparing the stress distribution of the inner lining and fiber winding layer of the cylinder before and after self-tightening.The results showed that the self-tightening treatment could effectively take advantage of the mechanical properties of carbon fiber,reduce the stress of the gas cylinder lining and improve the stress distribution.The optimal self-tightening pressure of LNG cylinders was 37 MPa by self-tightening optimization.The maximum Mises stress of LNG cylinder liner after optimizing the self-tightening pressure was increased by 33.2% and 27.7% under working pressure and water pressure;the maximum Mises stress of the composite layer was increased by109% and 45%,respectively.The bearing capacity of the gas cylinder under working pressure was increased by 33.2% and the utilization rate of the fiber layer was increased by about 1.1 times.The self-tightening process could effectively exert the mechanical properties of carbon fiber to ensure the use safety of LNG cylinders.(4)Gas cylinder preparation and water pressure bursting test.LNG cylinders were prepared through a wet winding process,and then hydraulic blasting was carried out on the cylinders to test the internal pressure of the ultimate bearing capacity,and finite element optimization and comparison were conducted.The results showed that the bursting pressure of the LNG cylinder was 57 MPa,which was consistent with the model prediction results.