Study On Composite Cylinder Flaw Mechanical Pronerties And Progressive Failure Based On ACP

Compared with the traditional metal cylinder,composite cylinder has the advantages of high strength and stiffness,lightweight,durable life-cycle and low cost.It is mainly used in aerospace,new energy automobile industry,civil equipment and industrial gas fields.Although there are many researches on the mechanical properties,defects and blasting pressure prediction of composite gas cylinders,there are still many results that need to be refined.In many studies,the defect modeling method of segmentation region is tedious counter-intuitive parameterization,and the continuous change of filament winding angle of the heads and the simultaneous failure of the metal liner and the composite layer cannot be considered.Meanwhile the maximum stress and strain criteria are commonly used in the finite element prediction of the ultimate strength of gas cylinders,which does not consider the progressive failure process of fiber layers.Hence,this paper studies the structure and mechanical properties of composite gas cylinder by combining theory with finite element modeling.The structure of gas cylinder was established by ACP software,and the parameters of winding angle,thickness and number of layers of filament winding layer were determined.In this paper,the auto-frettage pressure is optimized according to the DOT-CFFC cylinder standard,and the range of auto-frettage pressure is determined to explore the stress optimization results.It is estimated that the auto-frettage of this cylinder is about 28.8mpa.Three types of defect grids are established.Based on the design blasting pressure of 44.2MPa,the influence of the various stress of the fiber layer and the equivalent stress of the inner lining is analyzed.It is found that the defect will significantly increase the stress in the axial adjacent area and decrease the stress level in the circumferential area.The influence of defect size and position on stress's amplitude is small,while the influenced size is large,and the influence of defect depth is great.There is stress concentration in the defect area of both the liner and winding layer,but the effect of the defect on the equivalent stress of the liner is much less.The progressive damage simulation method is used to analyze the failure process of gas cylinder.The matrix cracking occurred earlier in the composite layer and extended to both ends.It then appears at both ends of the head.The fracture damage of fiber occurs later.From the beginning of local fracture,the stress of fiber in other areas continues to redistribute,and the fracture continues to expand outward and radially to both ends,which makes the bearing capacity of gas cylinder greatly reduced.With the increase of stress,the internal liner breaks at the initial position of local fracture,and finally the whole structure fails.The predicted bursting pressure is 60MPa,and the two experiments verify that the bursting pressure is 56.3mpa and 57.0mpa respectively,with an error rate of 5%.It can be considered that this method can predict the ultimate strength of gas cylinder well.