Johns Hopkins University (JHU) scientists have developed a new method for pinpointing cracks in metals before they become catastrophic.
Testing metals at a microscopic scale allowed them to rapidly inflict repetitive loads on materials while recording how ensuing damage evolves into cracks.
“We’re able now to have a more fundamental understanding about what leads up to cracks,” says team lead and JHU professor Jaafar A. El-Awady.
“The practical implication is that it will allow us to understand and predict when or how the material is going to fail.”
Called ‘cyclic loading’, this continuous change which refers to the pounding of vehicles on bridges or shifts in air pressure on airplanes, gradually induces slips in the internal molecular structure of the most durable metals.
These slips end up becoming cracks that could have been anticipated long before their perilous appearance, contends El-Awady:
“Fatigue failure plagues all metals and mitigating it is of great importance. It is the leading cause of cracks in metallic components of aircraft.”
That is why the airline industry often adheres to regular – and expensive – replacement schedules for many parts.
What the JHU team contends is that the life of those parts can be more accurately determined by better understanding the origins of crack initiation.
“With the lack of understanding of the mechanisms that lead to crack initiation, it has been difficult to predict with any reasonable accuracy the remaining life of a cyclically loaded material,” explains El-Awady.
“The component could actually be fine and never fail but they throw it away anyway solely on the basis of statistical arguments. That’s a huge waste of money.”
According to the scientists, current tests focus on the moments just prior to or after cracking to assess what happened in the makeup of the metal.
But these are mainly used on larger samples that preclude tracking the initiation of damage, which is a sub-micrometer scale feature.
El-Awady believes their method narrows the lens as small as feasible and begins when metals are first exposed to loads, helping mitigate cracks.
Image and content: NTSB/Johns Hopkins University