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Simulation of All-steel CNG Cylinders Fracture in an Impact by Damage Mechanic Approach

M. Yazdani Ariatapeh, M. Azadi, M. Mashayekhi and S. Ziaei Rad

Journal of Petroleum Research, Volume 24, Issue 78, March 2013, Pages 4-17



The high cost and risk of empirical tests on CNG cylinders make the use of numerical methods inevitable. In this paper, damage mechanics approach is used to investigate the effect of crash and damage caused by impact in CNG all-steel cylinders. The CSA standard in CNG cylinders is used as a damage detection criterion and cylinder ability to reuse. The simulation of cylinder failures caused by collision and drop is done by using Johnson-Cook damage model which is one of the efficient models in impact problems. Accomplished simulations are carried out in different impact directions, and the effects of cylinder internal pressure, collision velocity, and fall height are analyzed. Also, failures due to collision for various situations are discussed. These investigations for different cases, including crash and drop tests show that the maximum damage created in case of vertical impact and the resultant damage by changing direction from vertical to horizontal will be decreased. Furthermore, by eliminating failed elements and comparing damage depth caused by collision with CSA standard, it is observed that, in most cases of vertical accident and drop tests, the cylinders have been damaged and lost their ability to be used, while in horizontal impact cases the cylinders are intact or can be reused after repairing. The results show that, in collision process, the cylinder rear wall and the front hemisphere of the cylinder have further damaged and are the critical areas in the horizontal and vertical collisions respectively. For a specific impact direction in lower cylinder internal pressure, the damage caused by higher collision velocity and a higher altitude of falling will be more serious. The resulted diagrams indicate that the damaged area of the cylinders predominately are under compression and endure large plastic deformation. The low difference between the results by various meshes shows that this solution does not depend on the mesh size. Therefore, this damage model is insensitive to meshing in the various impact cases.



A. All-steel CNG cylinder; B. Damage Mechanics; C. Fracture; D. Impact; E. Finite Element Method


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