Failure analysis and finite element simulation of deformation and fracture of an exploded CNG fuel tank Majid Mirzaei ⇑ , Mohammad Malekan, Ehsan Sheibani Department of Mechanical Engineering, Tarbiat Modares University, Tehran, Iran article info Article history: Received 12 November 2012 Received in revised form 19 January 2013 Accepted 21 January 2013 Available online 29 January 2013 Keywords: Crack growth Pressure vessel Dynamic stress analysis Moving load Explosion abstract This paper reports the analysis and simulation of the catastrophic failure of a compressed natural gas (CNG) fuel tank. The initial analyses of the deformation and cracking patterns, along with the observed fractographic features, were indicative of an internal gaseous com- bustion. Accordingly, a set of transient-dynamic elasto-plastic finite element (FE) analyses was carried out to simulate the structural response of the tank to a special type of combus- tion-induced dynamic pressure. The FE model was composed of 3D brick elements equipped with interface cohesive elements for crack growth analysis. Excellent agreements were found between the final simulation results and the observed deformation and frac- ture patterns. The simulation results clearly revealed that the observed failure characteris- tics, like the overall asymmetric deformation and fracture patterns, initiation and partial growth of parallel cracks at the same section, multiple cracking at the neck, and the self-sim- ilar growth of the main axial crack were all caused by traveling of a deflagration-induced sonic pressure wave from the neck towards the bottom of the tank. Finally, a comparison was made between the characteristics of deflagration-induced and detonation-induced deformation and fracture behaviors of closed-end cylinders. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The worldwide number of vehicles fueled by natural gas reached 15,000,000 in 2011, and the average annual growth rate of these vehicles in the ASIA–PACIFIC countries exceeded 38% [1]. The overwhelming majority of these vehicles use CNG (compressed natural gas) fuel tanks. Although the proper design, manufacture, quality control, transportation, and imple- mentation of CNG cylinders have been specified by various standards and regulations [2–7], the number of accidental burst or even explosion of these cylinders is significant. Recently, the Civil Society Front Pakistan (CSF) has published a report, stat- ing that more than 2000 people have died in CNG cylinder explosions in Pakistan in 2011, and the figures are more likely to double in 2012 [8]. In spite of the significant number of reported CNG cylinder explosions worldwide [9–12], the available reports on systematic failure analysis of these cases are quite scarce [13,14]. Currently four different types of tanks are in service (see Fig. 1). Type 1 is a simple seamless metallic cylinder [15], Type 2 is a metallic cylinder (liner) with an overwrap of carbon fiber or fiberglass in the hoop direction over the cylinder sidewall [15], Type 3 is a metallic cylinder with an overall (including the domes) overwrap of carbon fiber or fiberglass [16], and Type 4 is a non-metallic cylinder with an overall (including the domes) overwrap of carbon fiber or fiberglass [17]. In 2009 a Type 1 tank exploded on board a sedan during refilling in a gas station in Iran. As a result of this catastrophic failure the car was partially destructed as shown in Fig. 2. Fortunately, the car had been evacuated prior to refilling so the incident did not cause 1350-6307/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.engfailanal.2013.01.015 ⇑ Corresponding author. Tel.: +98 21 82883357; fax: +98 21 82880000. E-mail addresses: mmirzaei@modares.ac.ir, majidmirzaei@hotmail.com (M. Mirzaei). Engineering Failure Analysis 30 (2013) 91–98 Contents lists available at SciVerse ScienceDirect Engineering Failure Analysis journal homepage: www.elsevier.com/locate/engfailanal