| Fiber reinforced composites is a new type of material with low density, high strength/stiffness-to-weight ratio, which is widely used in pressure vessels like the pressure pipe and the high-pressure gas cylinder. The failure process of composite is a damage accumulation process. There are various damage modes existing in composites, such as the interface debonding, matrix cracking, fiber breakage and delamination. When the damage behavior occurs in the composite, the properties of the material will be degraded and exhibit a progressive failure process. Besides, the composite, consists of the resin and the fiber which are inhomogeneous in the micro scale, shows severely anisotropic in the macro scale. These attributes make the analysis of composite cylinder more complicated. Because the gas cylinders are more and more widely applied into the industry and daily life, the safety and reliability of the gas cylinders earn more and more concern. Unfortunately, the methods that can predict the failure behavior under overload and impact load with acceptable precision are still unavailable.In this thesis, a3D finite element model of the full-wrapped composite cylinder was firstly created, and the progressive damage analysis method was imbeded in the program.The progamsuccessfully predicted the failure process and the burst pressure of the gas cylinder. Furthermore, the progressive damage method was integrated to analyze the impact behavior of the gas cylinder, and the influence of impact behavior on damage and load-carrying ability of the gas cylinder was investigated. The results demonstrate:(1) Only under the flow pressure load, the hoop-wrapped composite layers mainly born the circumferential stress, while the spiral-wrapped composite layers born the axial stress. With the increment of the flow pressure, the resin cracking first took place in the spiral-wrapped layers of the gas cylinder. After all the spiral-wrapped layers suffereed the resin cracked, the hoop-wrapped layers appeared the initial resin damage. The resin crack on the head gradedly happened from the end part to the middle part.(2) The damage of the fiber breakage first occured at the joint of the cylinder and the head, then spread to the main body of the cylinder. Besides, the fiber breakage is prone to happen on the hoop-wrapped composite layers. The composite layers of the head had no the fiber breakage until the overall collapse of the cylinder except the transition part of the cylinder and the head. Bases on the progressive failure analysis model, the predicted burst pressure of the gas cylinder was114MPa, which is in good agreement with the minimum tested burst pressure102MPa.(3) The dropping has severe effects on the transition part of the gas cylinder than any other location, and causes the resin crack and fiber breakage damage in this area, while the main cylinder part only suffer the slight damage. The resin cracking appeared primarily on the outward composite layers, especially on the spiral-wrapped ones. After dropping, the gas cylinder was furtherserved under the flow pressure. The resin cracking was expanded from the damaged elements and layer to the adjacent elements and layers. When droping at a velocity of20m/s, th residual carrying ability of the gas cylinder decrease by15.7%to96MPa.(4) Crash leads to serious local damage to the gas cylinder. At the crash area, the interior composite layers are usually damaged by the tense stress, and the outward composite layers are usually damaged by the compress stress. When it was served under the flow pressure after crash, the damage on composite expanded from the outward layers to the interior layers, which is contrary to a non-crashed cylinder. The residual carry ability of the gas cylinder, suffering the crash by a speed of lOm/s, was decreased by17.5%to90MPa in comparison with an intact one. |
