Effect of the Time Dependent Loading of Type IV Cylinders Using a Multi-scalemodel

The current requirements for composite cylinders are still based on an arbitrary approach derived from the behaviour of metal structures, that the designed burst pressure should be at least 2.5 times the maximum in-service pressure. This could lead to an over-designed composite cylinder for which the weight saving would be less than optimum. Moreover, predicting the lifetime of composite cylinders is a challenging task due to their anisotropic characteristics. A federal research institute in Germany (BAM) has proposed a minimum load-cycle requirement that mitigates this issue by using a MonteCarlo analysis of the burst test results. To enrich this study, more experiments are required however they are normally limited by the necessity of long duration testing times (loading rate and number of cylinders) and the design (stacking sequence of the composite layer). A multi-scale model incorporating the micromechanical behaviour of composite structures has been developed at Mines ParisTech. The model has shown similar behaviour to that of composite cylinders under different loading rates. This indicates that the model could assist the Monte-Carlo analysis study. An evaluation of the multi-scale model therefore has been carried out to determine its limitations in predicting lifetimes of composite cylinders. The evaluation starts with the comparison of burst pressures with type IV composite cylinders under different loading rates. A μCT-Scan of a type IV cylinder has been carried out at the University of Southampton. The produced images were analysed using the Fast-Fourier Transform (FFT) technique to determine the configuration of the composite layers, which is required by the model. Finally, the time dependent effect studied, by using the multi scale model, has been described. In the long-term, this study can be used to conduct a parametric study for creating more efficient design of type IV cylinders.