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- Artificial aging (1)
- Composite cylinder (1)
- Confidence level (1)
- Degradation trace (1)
- Distribution function (1)
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Composite materials show a degradation of properties depending on service life. This creates the necessity to find tailored methods to determine strength and residual strength of composite cylinders. The determination can be done e.g. by load cycles tests. The result needs a statistical assessment for the precise description of strength. Especially the statistical assessment of load cycle strength properties has a high uncertainty. It is unclear if a Log-Normal distribution, a WEIBULL distribution or others, describe the scatter behaviour of residual strength properties correctly.
Distribution functions aim at approximating the frequency of occurrence of residual load cycle strength for high survival rates. An assumption has to be found and confirmed to prevent over-estimation of reliability.
Gas cylinders made from composite materials receive growing popularity in applications where light weight is of advantage. At the same time manufacturers are interested in cutting cost and weight through material reduction for better acceptance of a product, e.g. H2-vehicles. This requires a better understanding of safety relevant properties.
The safety determination of current standards is mainly based on the minimum burst pressure of a few specimens. Various research projects were conducted aiming at reducing minimum burst pressure requirements without compromising safety. No satisfying results were found. While looking at reliability aspects it could be concluded, that the minimum burst pressure of unused specimens is not a satisfying criterion for safety during service life.
This paper introduces first ideas for a method to determine one aspect of reliability of composite gas cylinders, employing probabilistic analysis of burst pressures of a sample of specimens. This can create potential for saving material cost while granting a higher safety level than the current method. Additionally, degradation over service time can be assessed.
Composite materials show a degradation of properties depending on Service life. This creates the necessity to find tailored methods to determine strength and residual strength of composite cylinders. The determination can be done e.g. by load cycles tests. The result needs a Statistical assessment for the precise description of strength. Especially the Statistical assessment of load cycle strength properties has a high uncertainty. It is unclear if a Log-Normal distribution, a WEIBULL distribution or others, describe the scatter behaviour of residual strength properties correctly. Distribution functions aim at approximating the frequency of occurrence of residual load cycle strength for high survival rates. An assumption has to be found and confirmed to prevent overestimation of reliability.