Study On Mechanical Properties Of Composite Cylinder Under Different Winding Technology

The composite cylinders have been successfully applied in many fields,due to its advantages of lightweight,high strength and good anti-fatigue performance.However,there are still many deficiencies in the structural design and performance analysis of composite cylinders.For example,in the case of damage failure of composite cylinders,only analyzing the failure modes of the composite layer,scholars don’t give an overall configuration of the failure process.In the case of non-geodesic winding of composite cylinders,the study which merely considers changing the winding angle ignores the influence of the spiral wound angle on the redistribution of the thickness of the winding layer.In the case of the shoulder accumulation of composite cylinders,reaming is adopted to reduce the fiber accumulation in the shoulder of the bottle by winding experience in engineering.However,there are few theories concerned.Aiming at the above shortcomings,this paper which uses the procedure of theoretical analysis and numerical simulation analyzes the structure and performance of composite cylinders.The main work and results are as follows:(1)The progressive damage method is used to simulate the whole failure process of composite cylinders.The matrix crack firstly appears on the cylinder composite layer and expanded from equal thickness section to the two ends.However,it appears later on the head and expanded from both ends to the center.After the matrix is completely cracked,the fiber on the cylinder remains intact.The internal pressure continues to increase.When a certain value is reached,the fibers on the cylinder are partially broken.Different from the direction of extension of the matrix,except for breaking from the initial position to the two ends,the fiber fracture also expands locally along the radial direction.Fiber breakage greatly reduces the bearing capacity of the cylinder.The deformation of the liner at the initial position of the fiber fracture increases and then breaks,resulting in the overall failure of the cylinder.The final bursting pressure of this kind of cylinder is calculated to be 112 MPa,which is close to the experimental value 108 MPa.(2)According to the requirement of DOT-CFFC standard,the range of auto-frettage pressure of composite cylinder is determined.On this basis,the effect of auto-frettage pressure on fatigue life of the gas cylinder is studied in this paper.The results show that the equivalent stress amplitude increases with the increase of auto-frettage pressure on equal thickness section of liner.Thus,the optimum auto-frettage pressure of this kind of cylinders is determined to be about 54 MPa.(3)Aimed at the insufficient research on non-geodesic,this paper takes account in the influence of winding angle on the redistribution of the thickness of the winding layer.Through the analysis of the non-geodesic theory of the head,the allowable range of the deviation angle is obtained.Then,according to the influence of the deviation angle on the strain of the cylinder,the optimum value is determined.On this basis,the paper utilizes stress analysis and progressive damage method discusses the influence of non-geodesic winding on the mechanical properties of gas cylinders.The results show that the non-geodesic winding not only does not change the ultimate bearing capacity of the gas cylinder,but also increases the strength of the head.For this kind of cylinder,When the cylinders are made with the best deviation angle,under nominal working pressure,the mises stresses of the inner and outer walls of the head which is near the polar hole are respectively reduced by an average of about 6.4% and 4.3% under nominal working pressure。With different deviation angles,the bursting pressures of cylinders are all 112 MPa,which is the same as that of the geodesic winding cylinders.(4)Aimed at the problem of bottle shoulder accumulation,this paper puts forward the method of bandwidth-reaming and extremum-reaming.It is found that reaming can not only reduce the fiber accumulation near the polar hole,but also make the fiber distribution on the head more uniform.By comparing different types of reaming,the thickness of the fiber,to the maximum extent,can be reduced by means of bandwidth-reaming.By comparing the simulation results of different reaming models of this kind cylinder,it is found that the effect of the reaming form,one bandwidth and one-and-a-half bandwidth each of which reams once,is best.It can reduce the overall stress level of the cylinders on the basis of guaranteeing that the thickness of the fiber is reduced by 31.5%.Through progressive damage analysis,it is found that the reaming technique improves the ultimate load-carrying capacity of the cylinders.For this purpose,reaming can not only reduce the shoulder accumulation,but also increase the whole strength and ultimate load capacity of the cylinder in appropriate circumstances.