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The idea of indestructible killer robots might sound like something straight out of the Terminator movie.
But they could soon become a reality, as scientists have just seen for the first time how metal heals itself, without any human intervention.
One based in the US study has undone everything we thought we knew about metals by revealing that wear cracks can repair themselves under certain conditions.
It’s a discovery that has the potential to revolutionize engineering, with the prospect of self-healing engines, airplanes and even robots now on the horizon.
“This was absolutely stunning to see firsthand,” said Brad Boyce, a scientist at Sandia National Laboratories who led the study with Texas A&M University.
The idea of indestructible killer robots might sound like something straight out of the Terminator movie
Scientists spent 40 minutes on the experiment when the damage reversed as a ‘t-junction’ crack merged back together as if it had never been there
“What we’ve confirmed is that metals have their own intrinsic, natural ability to self-heal, at least in the case of nanoscale fatigue damage.”
Metals currently used to build vital infrastructure, such as bridges and airplanes, undergo a lot of repeated stress and movement, causing microscopic cracks to form over time.
While this fatigue damage usually causes machines to break, Mr. Boyce and his team saw the nanosized fracture shrink by 18 nm.
This was a completely unexpected discovery, as scientists only wanted to evaluate how cracks would propagate through a 40nm-thick piece of platinum when pressure was applied.
They were 40 minutes into the experiment when the damage reversed, when a “t-junction” crack merged back together as if it had never been there.
When more pressure was applied, the crack grew back in a different direction, as puzzled scientists watched through a microscope.
“From solder joints in our electronic devices to the engines of our vehicles to the bridges we drive over, these structures often fail in unpredictable ways due to cyclic loading leading to crack initiation and eventual fracture,” continued Mr Boyce.
“If they do fail, we incur replacement costs, lost time, and in some cases even injury or death. The economic impact of these failures is measured in hundreds of billions of dollars for the US each year
As more pressure was applied, the crack grew back in a different direction, as amazed scientists observed through a microscope (pictured)
“Cracks in metals were only expected to get bigger, not smaller. Even some of the basic equations we use to describe crack growth rule out the possibility of such healing processes.”
While much is still unknown about self-healing, scientists believe a process known as cold welding may have played a role.
This can occur at the point of metal fatigue, which allows bare metals to “join together” when compressed under contact.
Their study comes 10 years after Michael Demkowicz, of the Massachusetts Institute of Technology, advanced a similar theory about self-healing metals.
He promoted the idea that nanocracks rely on the generation of crystal defects known as ‘disclinations’ to heal in metals.
In this study, researchers also recognized that different crystalline materials with different grain shapes and textures can be affected in different ways by this.
Their nano-sized platinum was tested primarily in non-oxygen conditions, so they believe there is an opportunity to explore non-vacuum conditions even further.
Mr. Boyce continued: ‘The extent to which these findings are generalizable is likely to become the subject of extensive research.
‘We show that this happens in nanocrystalline metals in a vacuum. But we don’t know if this can also be induced with conventional metals in air.’
Ten years after his own study, Mr. Demkowicz praised this latest research and expressed his hopes for the future.
He said, “I hope this finding will encourage materials researchers to consider that materials, under the right conditions, can do things we never expected.”