New testing method improves composites understanding

The Fraunhofer Institute for Structural Durability and System Reliability LBF has developed a new testing method which combines mechanical and radiographic examination.

The method can be used to characterize materials, and reportedly makes it easier to assess inclusions or damage to raw material based on their influence on the durability and service life. Fraunhofer LBF says this can lead to better understanding of material behavior and material characterization.

Using the 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 analyzed throughout the entire load duration. Previous concepts were not able to achieve the necessary precision of just a few micrometers with the alternating insertion and removal of the sample with intermittent radiological examination, Fraunhofer says.

‘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,’ said Oliver Schwarzhaupt, scientific employee in function-integrated lightweight construction at Fraunhofer LBF. ‘The new process represents a huge advance in regards to detail resolution and precision, as well as the retrievability of possible causes of damage.’

While scientists subject the component to a mechanically dynamic service life load, they can use the radiological examination in this 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 fiber like those used in aircraft construction can be examined, the scientists say. ‘There is still a great need for examination to understand the failure mechanisms in carbon fiber-reinforced plastics,’ said Schwarzhaupt.

Damage origin

With most modern imaging processes, cracks and damage in material can be illustrated vividly and in three dimensions, opening up many possibilities for analysis. With the use of a microfusion pipe, the x-ray equipment in the Fraunhofer LBF has a high resolution capacity of just a few micrometers. In this way 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 fiber-reinforced plastics in particular, the occurrence of damage on the fiber 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,’ ensures Schwarzhaupt.

This story is reprinted from material from Fraunhofer, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.