Radiographic Inspection of Components Made of Fibre-Reinforced Plastics
In future, the failure of carbon-fibre-reinforced plastics can be observed live on each fibre. Researchers at Fraunhofer LBF have succeeded in combining mechanical component testing with radiographic testing under realistic loads. This method facilitates the assessment of inclusions or damaged areas in the material with regard to their impact on strength and durability and is used to categorise materials. This gives material developers and manufacturers important information on improving their understanding of material behaviour and properties.
"Understanding how damage arises in the material of a component while it is subject to realistic mechanical loads is one of the most important questions in material science and has so far not been possible to understand in this way", emphasises Oliver Schwarzhaupt, research fellow from the Department of Lightweight Structures at Fraunhofer LBF. In the new test method, the tested component remains in the X-ray system during mechanical loading, allowing the exact location in the material to be observed and analysed for the entire duration of the loading.
Discovering the origins damage quickly
With previous concepts, the required accuracy of a few micrometres could never be achieved due to having to alternately insert and remove the sample for intermediate radiographic testing. "The new process represents a great advance in terms of detail resolution, accuracy, and finding possible causes of damage", Schwarzhaupt explains.
While the Darmstadt scientists subject the component to mechanical and dynamic endurance testing, they can observe and present the emergence and progress of a flaw by radiographic testing in this cycle. Using the test machine, which can apply up to 250 kilonewtons of force, it is also possible to examine high-strength carbon-fibre-reinforced components as used in aircraft construction, in particular. "There is still a lot of research to be done on failure mechanisms in carbon-fibre-reinforced plastics", Schwarzhaupt emphasises.
Representing cracks and damage in 3D
Using state-of-the-art imaging techniques, cracks and damage to the material can be depicted visually in three dimensions, thereby opening up many possibilities for analysis. Due to the use of a microfocus tube, the X-ray system at Fraunhofer LBF has a high resolution capability of a few micrometres. In this way, it is possible to detect very fine damage from the very beginning of the production process, or determine where damage formed based on the smallest irregularities in the material as the location. Damage formation at fibre level can be investigated especially in the field of fibre-reinforced plastics.
Primed with this knowledge of the formation and progress of the failure, developers, designers and manufacturers can now improve their materials, components and manufacturing processes even before, for example, a crack becomes visible to the naked eye. "With this new method, we’re making a great contribution to understanding materials and can respond to customer-specific requirements in the area of material failure much better and at an earlier stage", Schwarzhaupt affirms.