Researchers from IMDEA Materials and the Carlos III University of Madrid (UC3M), in collaboration with research institutes in France and Japan, have achieved a significant breakthrough in better understanding the fracture mechanics of additively manufactured metals.

The results, outlined in the Journal of the Mechanics and Physics of Solids, showcase in-situ, real-time X-ray observations of how two of the most widely utilised aluminium and titanium alloys react when subject to high-velocity loading.

The findings not only establish a direct connection between pore-scale mechanisms and macroscopic fracture response, but also present opportunities to improve the impact behaviour of 3D-printed alloys.

The research focused on AlSi10Mg and Ti-6Al-4V, two commonly used alloys in Laser Powder Bed Fusion (LPBF) additive manufacturing.

This technique enables the production of complex geometries layer by layer. However, the process can also introduce microscopic pores within the material. Understanding how these defects behave under extreme loading conditions has, until now, remained a significant challenge.

This research is particularly important for applications in aerospace, transport and defence, where components are frequently exposed to intense dynamic loads.

“This approach allows us to directly observe how damage forms and evolves inside additively manufactured metals during extreme loading,” explained Dr. Federico Sket, Senior Researcher at IMDEA Materials Institute and one of the authors behind the publication.

Meanwhile, Prof. José A. Rodríguez Martínez, Professor at UC3M, Visiting Scientist at IMDEA Materials and coauthor added that, “for the first time, we can connect what happens at the microscopic scale with the macroscopic signals measured during impact experiments”.

Specifically, researchers were able to observe, in real time, how the microscopic pores left behind in 3D-printed metals collapse, reopen and ultimately trigger fracture during high-velocity impacts.

The experiments were performed at the European Synchrotron Radiation Facility (ESRF), one of the world’s leading facilities of its type, where researchers used intense X-ray beams to look inside the metals while being struck at velocities of up to 750 metres per second.

Using ultrafast X-ray phase-contrast imaging with nanosecond time resolution, the researchers observed the full sequence of events inside the metal during impact.

Initially, the shock wave compresses the material, causing pores to collapse.

As stress waves propagate and the material experiences tension, the pores reopen and grow. Eventually, they link together, forming an internal crack that leads to a phenomenon known as Spall Fracture.

Unlike normal fractures, which usually start at the surface, spall fracture forms inside the material due to the behaviour of stress waves. As they form inside the material rather than on the surface, these cracks are generally harder to detect and analyse.

And, while the AlSi10Mg and Ti-6Al-4V alloys exhibited clear differences in their individual fracture morphology, both were governed by the same underlying damage mechanism involving void growth and coalescence leading to internal fracture.

“Altogether, this paper provides new insights into dynamic tensile fracture of 3D-printed metals,” explained fellow IMDEA Materials researcher Dr. Javier García Molleja.

“It does so by leveraging the latest advances in fast X-ray phase-contrast imaging and high-resolution tomography, while establishing a systematic protocol to investigate void collapse and spall failure mechanisms in porous materials subjected to shock loading”.  

Additionally, this approach opens new perspectives in the application of additively manufactured metals for protection and energy absorption applications, highlighting their potential for next-generation engineering solutions.

Alongside IMDEA Materials Institute and the UC3M, the publication also relied on contributions from the ESRF-European Synchrotron, the Max von Laue-Paul Langevin Institute in France, and the Japan Synchrotron Radiation Research Institute (JASRI).

The researchers propose that the experimental framework presented should be extended in future to other grades of aluminium and titanium alloys suitable for additive manufacturing, as well as to lightweight printed metals such as magnesium.