High-speed photos shine a light on how metals fail

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High-speed photos shine a light on how metals fail
An alloy sample being stretched in front of the laser-high speed camera set up. Credit: Aalto University

How things deform and break is important for engineers, as it helps them choose and design what materials they’re going to use for building things. Researchers at Aalto University and Tampere University have stretched metal alloy samples to their breaking point and filmed it using ultra-fast cameras to study what happens. Their discoveries have the potential to open up a whole new line of research in the study of materials deformation.

When materials get stretched a bit, they expand, and when the stretching stops, they return to their original size. However, if a material gets stretched a lot, they no longer return back to their original size. This over-stretching is referred to as ‘plastic’ deformation. Materials that have begun to be plastically deformed behave differently when they’re stretched even more, and eventually snap in two. Some materials—including the lightweight aluminum alloys used in high tech applications like cars and aircraft—start to deform unpredictably when they become plastically deformed. The specific problem the researchers were interested in solving is called the Portevin-Le Chatelier (PLC) effect, where bands of deformation in the material move as it gets stretched. The movement of these bands causes the unpredictable deformation, and researchers wanted to develop a better understanding of how they moved, to be able to better predict how these materials would deform. “There were models for how these materials deformed,” said Professor Mikko Alava, the leader of the research group at Aalto, “but until now, they weren’t very useful.”

To develop the new model, the researchers used very high-speed cameras, illuminated using laser light, to photograph the samples. Once they gathered this data, they were able to see what theoretical models fit the data. They found that