New analysis methods provide important knowledge about metal cracks

Thursday 24 Sep 20


Grethe Winther
Head of Section, Professor
DTU Mechanical Engineering
+45 45 25 47 55


Typical cracks from shaping of flat metal sheets. The figure shows porosities (marked as white) which form, grow together to form cracks and final fracture.

With a completely new X-ray analysis, DTU researchers will develop material models for use in companies that make metal products. The result means reduced material consumption and faster product development.

It is well known that metal can develop cracks when forged and shaped into a product. Until now, however, it has not been known why and where the first porosities that develop into cracks occur. A newly developed X-ray analysis now makes it possible to study the interior of a metal while it is being shaped. This allows researchers to determine exactly where in the metal the porosities are formed and how they develop.

“The new method makes it possible to see into the metal in 3D and examine its interior, almost like in a film. This occurs while we shape the metal—in practice, it means that the metal bar we’re examining under the microscope is being pulled longer and longer. While this happens, we can observe when and where the porosities form and grow,” says Professor Grethe Winther, DTU Mechanical Engineering, who heads the new project.

The new X-ray analysis method has been developed by Professor Henning Friis Poulsen, DTU Physics, who is also attached to the project.

Existing models to be expanded with new knowledge
Once the researchers have mapped the small porosities that form in the metal—and that subsequently grow together to become cracks—the next step will be to expand the existing metal behaviour models with this knowledge.

“Knowledge of porosities gives us insight into the tension and rotation of the small crystals of which the metal is composed. This insight is completely new and is to be added to the current models. We will do this in collaboration with the German Max Planck Institute in Düsseldorf, which—for many years—has developed modelling software that is widely used among researchers worldwide,” says Grethe Winther.

However, the work does not end with the final development of the material model. The new knowledge about the microscopic details in the crystals of the metal will subsequently be also be applied in the work with metals of the sizes that companies use.

The material model will therefore be implemented in process simulation software which can be used directly in the industry.

“For this part of the project, we’ve also chosen to use software for our solution which is already used by many companies that manufacture metal products. In this way, we hope that our new knowledge can be used to the greatest possible extent,” says Grethe Winther.

Accelerated product development
Metal shaping is a complex process, and it is therefore difficult for many companies to predict what happens if—for example—they want to change one of their metal products from square to hexagonal.

“With the coming improved digital option, companies no longer need to develop a wide range of prototypes and then proceed by trail and error in their product development. Instead, they can perform a whole series of tests with a PC in a short period of time, and then quickly determine whether the idea for a new product is feasible,” says Grethe Winther.

Simulations can also contribute to establishing whether the current metal is the most optimal choice for the company's product or whether it would be better to purchase a slightly different material. It can also be ascertained whether the quantity of metal used in a product can be reduced because too large quantities have been used so far to ‘be on the safe side’.

The development of the new metal models for process simulation has just started and will last for the next four years. The work has been supported financially by Independent Research Fund Denmark with DKK 6.1 million.
21 OCTOBER 2020