Residual Strength of Composite Pressure Vessels After Impact
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Composite overwrapped pressure vessels are increasingly being applied for transportation and storage of pressurized fluids. With superior material properties, fiber-reinforced composites are central to increasing operating pressures and safety factors, while also reducing operational costs. The advantages of applying composite materials are, however, yet to be fully utilized, as there is still need for further understanding of failure and residual behaviour of composite structures sustaining damages. By developing predictive FE models able to confidently assess residual performance, the aim is to reduce uncertainty and expenditures, while increasing safety and lifetime utilization. This master's thesis investigates the residual tensile strength of type IV carbon fiber pressure vessels with hole notch damages. The development of a new high-strength end-dome concept has allowed for tensile testing of composite vessels at forces close to 1000 kN, which has resulted in unique residual strength results for vessels with through laminate hole notches. Laminate composition, fiber volume fraction, effective layer thicknesses and effects of winding sequences has been revealed with microscopy analysis of the filament wound samples. A FEA model has been developed to replicate experimental results applying Hashin's failure criteria and a progressive failure methodology in commercially available FEA software Abaqus 6.14. Unique residual strength results for damaged composite vessels were obtained for several damage sizes, showing good agreement with expected trends and equivalent at laminate studies. A thorough parameter sensitivity analysis has been performed and documented through the numerical work to develop a generalized model able to replicate residual behaviour of damaged vessels. This model currently provides an accuracy within a 19% range (mostly conservative) compared to experimental results, and is applicable for other damage sizes with an accuracy within a 12% range. Such predictive models may contribute in increasing safety and lifetime utilization of composite overwrapped pressure vessels, while reducing uncertainties and both capital and operational expenditures.