Damage Morphology And Residual Strength Of Composite Cylinder Under Impact

Composite cylinders,which have the advantages of light weight,good fatigue resistance and high safety,play an important role in many fields such as aircraft,vehicle-mounted high-pressure cylinders and petrochemical industry.During usage,composite cylinders may suffer from various forms of defects such as matrix cracking,fiber fracture and delamination failure due to impact,drop or scratch,which lead to the decrease of carrying capacity of the whole structure to some extent,causing a safety risk.There are many reasons for the failure of composite materials,and failure forms are complex.Previous studies in this field mostly focus on simple structures such as composite laminates,and there are less analyses of the whole structural failure of composite cylinder.Therefore,it is of great significance to study the effect of different damage morphology on the residual strength of composite cylinder and assess the damage level of composite cylinder.The main contents and achievements of this paper are as follows:(1)Basic mechanical theory and the failure criterion of composite cylinder were based on and the finite element analysis model of composite cylinder was established.The Camanho parameter degradation scheme was combined with Hashin failure criterion to simulate the whole process of progressive damage of cylinder.The simulated burst pressure of cylinder was 107 MPa,which was 3.6% different from hydraulic test burst pressure 111 MPa.The error was within a reasonable range,and the accuracy of the model was verified.(2)A finite element model which simulated the impact process of composite cylinder was established,and a progressive damage module was introduced to predict the residual burst pressure.The transient stress level of composite cylinder which suffered impacting,the damage of composite cylinder after impacting and the change of residual burst pressure were investigated.Taking the middle part of cylinder impacted by a steel ball weighs 0.89 kg with a radius of 3cm and a velocity of 10m/s as an example,there were 12 layers of matrix cracking and 3 layers of fiber fracture in the fiber winding layer after impacting;matrix failed earlier than fiber;the impact on the outside of fiber winding layer was greater than that on the inside,and the effect on middle layer was the least.After impacting,the residual burst pressure of cylinder was 81 MPa,and the carrying capacity was reduced by 24.3%.(3)Single variables were controlled,such as the velocity of impact object,the shape of impact object and the location of impact.It was found that the damage degree of composite cylinder increased with the increase of impact velocity;when the impact velocity was small,for instance,the impact velocity of small ball was less than 5m/s,only matrix cracking occurred,and the carrying capacity of composite cylinder almost did not change.Among impact objects with equal mass and velocity which was simulated in this paper,the damage degree to composite cylinder from large to small was hexahedron,sphere and cylinder respectively.The contact part between impact object and the surface of composite cylinder was sharper and the contact area was smaller,the damage to composite cylinder was greater.When the ball impacted composite cylinder at the same speed,the damage caused by impact in the transition section of composite cylinder was smaller than that in the middle section of composite cylinder.(4)A finite element model which simulated the drop process of composite cylinder was established.It was found that the stress in the area where composite cylinder contacted with the ground linearly was large,and the stress extended along hoop direction to both sides.The most serious damage of fiber winding layer was located at the junction between head and cylinder.Although there was no direct contact with the ground,the discontinuity of fiber force increased the damage degree.The damage gradually decreased from the joint between head and cylinder to the middle of cylinder.The damage to the outside of fiber winding layer was more serious than to the inside.The spiral winding layer was more prone to matrix cracking and the hoop winding layer was more prone to fiber breakage.(5)Simulated the horizontal drop process of composite cylinder.As the height of drop increased,damage degree of composite cylinder increased.The damage of fiber winding layers extended from the joint between head and cylinder to the middle of cylinder.When the height of drop was small,only matrix cracking occurred,and it hardly affected its carrying capacity,such as composite cylinder in this paper falling from 2m.When the drop height of composite cylinder exceeds 5m,the carrying capacity of composite cylinder had decreased.Taking composite cylinder falling from 5m and10 m as an example,the carrying capacity decreased by 7.5% and 17.8% respectively.