Ingenieurwissenschaften und zugeordnete Tätigkeiten
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Composite pressure vessels are important components in the storage of gases under high pressure. Among others, a common type of pressure vessel is made of a metal liner overwrapped with a fibre-reinforced plastic material. Conventional hydrostatic tests, used to assess the integrity of pressure vessels, may overstress the material and thus reduce the remaining lifetime of the tested component. Therefore, a truly non-destructive structural health monitoring (SHM) system would not only ensure a safer usage and extended lifetime, but also remove the necessity for periodic inspection and the testing of pressure vessels. The authors propose the use of guided ultrasonic waves, which have the potential to detect the main damage types, such as cracking in the metal liner, fibre breaks and composite matrix delamination. For the design of such an SHM system, multimodal ultrasonic wave propagation and defect-mode interaction must be fully understood. In this paper, simulation results obtained by means of finite element modelling (FEM) are presented. Based on the findings, suggestions are made regarding appropriate wave modes and their interaction with different flaw types, as well as the necessary excitation and suitable sensor configurations. Finally, a first approach for a reliable SHM system for composite pressure vessels is suggested.
The in situ analysis of the damage evolution in a metal Matrix composite (MMC) using synchrotron X-ray refraction radiography (SXRR) is presented. The investigated material is an Al alloy (6061)/10 vol% Al2O3 MMC after T6 heat treatment.
In an interrupted tensile test the gauge section of dog bone-shaped specimens is imaged in different states of tensile loading. On the basis of the SXRR images, the relative change of the specific surface (proportional to the amount of damage) in the course of tensile loading was analyzed. It could be shown that the damage can be detected by SXRR already at a stage of tensile loading, in which no Observation of damage is possible with radiographic absorption-based imaging methods.
Moreover, the quantitative analysis of the SXRR images reveals that the amount of damage increases homogeneously by an average of 25% with respect to the Initial state. To corroborate the experimental findings, the damage distribution was imaged in 3D after the final tensile loading by synchrotron X-ray refraction computed tomography (SXRCT) and absorption-based synchrotron X-ray computed tomography (SXCT). It could be evidenced that defects and damages cause pronounced indications in the SXRCT images.