TypeIII Carbon Fiber Reinforced Plastic (CFRP) pressure vessels are widely used as accumulators at the hydrogen fueling stations. To commercialize Fuel Cell Vehicles (FCV) , the cost of the CFRP accumulators needs to be reduced with safety. The safety of the CFRP pressure vessels have been mostly examined by the qualification and production tests so far since the Finite Element (FE) modeling of CFRP layers were not so sophisticated enough as to yield reliable failure analysis result. A key technology is a concise algorithm to cope with laborious modeling task for dome region where fiber orientations and the thicknesses of CFRP layers vary locally. We developed algorithm to describe the complicated layered structures with practical accuracy. Owing to the developed algorithm, we can constitute an optimization problem to reduce CFRP layers thicknesses with the stress constraint on aluminum liner, which governs the long time safety of the TypeIII vessels under cyclic pressure. We demonstrate the validity of the proposed algorithm through an optimum shape finding problem of dome. The optimum shape of the liner at dome region leads a reduction of CFRP thickness with satisfying allowable stress.

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In recent years, it has been common to perform a finite-element analysis focusing on the deformation with plastic strain after uniform elongation. For example, a simulation might be performed of the rupture in a smooth material that receives tensile deformation, or the fracture mechanical parameter around a crack tip might be evaluated. Although these analyses require a true stress-strain curve after uniform elongation as an input, a true stress-strain curve after uniform elongation cannot be obtained using a tensile specimen test conducted under the general procedures. This is because necking, which is strain localization, occurs just after uniform elongation, and the true stress-strain curve cannot be calculated from the nominal stress-strain curve. This study investigated the true stress-strain curve after the uniform elongation of line pipe steels. True stress-strain curves for various materials were obtained by measuring the deformation shape of the necking part during tensile tests. To select an appropriate approximate function for describing the true stress-strain curve after uniform elongation, the errors in the Hollomon (exponential law) , Ludwic, Swift, and Ramberg-Osgood functions were compared. The errors in the Ludwic and Swift functions were smaller than those for the Hollomon and Ramberg-Osgood functions when the curves described by these functions were best-fitted to the measured data. Additionally, the errors that occurred in the extrapolation of the true stress-strain curve were shown. In this extrapolation, the parameters for each function were determined using the best-fit to the relationship before the uniform elongation rather than afterward. The errors in the true stress by the extrapolation had values of 10% or more. Finally, a regression formula was proposed for the true stress-strain curve after uniform elongation. This formula is based on a Swift function, and its parameters can be calculated using only the fundamental material strength parameters, including the yield strength, tensile strength, and uniform elongation. The error in the true stress by this regression formula was about 4%.

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The bottom corner joint of welded steel tank for oil storage is the most important in the periodical opening inspection because the annular plate in the vicinity is particularly high stress region. Therefore, the strict inspection with water fill test is required when it is defective. So its zone was previously regulated conservatively as 1 foot of radial direction width which was defined as critical zone in API (American Petroleum Institute) Standard 653. And in recent years, it has been revised as 3 inches of short width in consideration of reduction of the inspection cost. But the critical zone in Japanese Fire Service Act still remains as 600mm width. In order to clarify the grounds for the values of critical zone and the rational values in engineering, the survey for three fiscal years has carried out in Center for Risk Management and Safety Sciences of Yokohama National University. The results are as follows:
1) Clarification of the grounds for conservative critical zone
2) Establishment of the rational critical zone based on stress analysis for several kinds of loads including earthquake
3) Offering a proposal for the rational critical zone according to defective degrees

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On April 17, 2013, a fire and explosion occurred at the West Fertilizer Company in West, Texas, USA. The violent detonation killed 15 emergency responders and residents and injured more than 260 people. The U. S. Chemical Safety and Hazard Investigation Board (CSB) released the report on the cause of this incident. The presence of combustible materials used for construction of the fertilizer grade ammonium nitrate storage facility contributed to the progression and intensity of the fire and resulted in the detonation. This paper describes the incident based on the CSB report.

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