WP2 - D2. 4 Report Summary of findings WP2 is focused on the material scale and all results reported below must be considered for composite material purposes although some references are given for composite pressure vessels. The WP2 concludes that large-scale fibre rupture clusters are the most critical damage to the structural integrity of composite materials dedicated to CPV cylinders. It was determined that the strength of the laminates was dependent on the total content of fibre rupture clusters de- veloping in the material. The long-term lifetime behaviour of the composites is highly de- pendent on the type of the epoxy resin used and the curing condition applied in the compo- sites, which affect visco-elasticity of the matrix. There are other factors that can affect the growth rate of damage clusters such as, applied stress level and environmental conditions. Findings for manufacturing composite pressure vessel cylinders Use epoxy matrix polymer with better resistance to stress relaxation (creep) process should effectively reduce the growth rate of fibre rupture clusters so as to retard material degrada- tion process in the structure and improve the lifetime performance Use epoxy matrix with the material properties, having lower dependency on the elevation of temperature, particularly when close to Tg. The effect of temperature must be taken into ac- count in the safety factor analysis since the rise of the temperature can affect the lifetime of the composites. Optimize the thickness of laminate ply of CPV cylinders for the consideration of fibre rupture clustering process. It was found that fibre rupture clustering process was more favourable in the laminate containing one thick 0°ply than multi ple thin 0°plies. Findings for acoustic emission evaluation There is no standardization for AE systems from different manufactures. In general, the pa- rameters (such as energy) used for setting-up AE acquisition are not identical between dif- ferent systems. For non-destructive evaluation of composite pressure vessels, to perform full-field monitoring on CPV cylinders, numbers of AE probes (or sensors) distributed over the cylinder surface have to be applied to facilitate quasi full-field monitoring on composite cylinders.
