New process analyses damage to raw materials under load with radiographic examination

The Fraunhofer Institute has developed a new method that it says combines the mechanical testing of a component under realistic loads with radiographic examination for the first time.

Especially useful for carbon fibre-reinforced plastics, the method is used to characterise materials, and makes it easier to assess inclusions or damage to raw material regarding their influence on durability and service life.

In so doing, Fraunhofer says it provides materials designers and manufacturers, as well as scientists, with information for better understanding of material behaviour and material characterisation.

“Understanding how damage occurs to the material of a component while is placed under realistic mechanical loads is one of the key questions in materials science, and was previously not possible,” explained Oliver Schwarzhaupt, scientific employee in Function-Integrated Lightweight Construction at the Fraunhofer Institute.

With the new test method, the tested component remains in the x-ray equipment during the mechanical load. As a result, the exact location in the material can be observed and analysed throughout the entire load duration. Previous concepts were never able to achieve the necessary precision of just a few micrometers with the alternating insertion and removal of the sample with intermittent radiological examination.

“The new process represents a huge advance in regards to detail resolution and precision, as well as the retrievability of possible causes of damage,” continued Schwarzhaupt.

While scientists at Fraunhofer are subjecting the component to a mechanically dynamic service life load, they can use the radiological exambination in the cycle to observe and illustrate the occurrence and progress of the damage. With forces in the test machine of up to 250 kilonewtons, even high-strength components made of carbon fibre can be examined. “There is still a great need for examination to understand the failure mechanisms in carbon fiber-reinforced plastics,” added Schwarzhaupt.

With the use of a microfusion pipe, the x-ray equipment at the Fraunhofer Institute has a high resolution capacity of just a few micrometers. This means it is possible to detect the smallest signs of damage even as it begins to occur, or determine that the slightest irregularities in the material are the point of origin for the damage. In the area of fibre-reinforced plastics in particular, the occurrence of damage on the fibre level can be studied.

With this knowledge about the cause of the error and the error sequence, developers, designers, and manufacturers can now improve their materials, components, and manufacturing processes even before a crack is macroscopically visible. “Our new concept makes a great contribution on the topic of material understanding and is clearly better able to meet customer-specific requirements in the area of material failures at an early stage,” concluded Schwarzhaupt.