Engineers can now capture and predict the strength of metallic materials subjected to cyclic loading or fatigue strength in hours – not in the months or years required with current methods.
In a new study, researchers at the University of Illinois Urbana-Champaign report that automated high-resolution electron imaging can capture the nanoscale deformation events that lead to metal failure and fracture at the origin of the metal failure. The new method helps scientists quickly predict the fatigue strength of any alloy and design new materials for engineered systems subjected to repeated loading in medical, transportation, security, energy and environmental applications.
The results of the study, led by materials science and engineering professors Jean-Charles Stinville and Marie Charpagne, are published in the journal Science.
Fatigue in metals and alloys — like the repeated flexing of a metal paper clip, causing it to break — is the leading cause of failure in many engineering systems, Stinville said. Defining the relationship between fatigue strength and microstructure is challenging because metallic materials exhibit complex structures with features in the nanometer to centimeter range.
“This multiscale problem is a long-standing problem because we’re trying to observe sparse, nanometer-sized events that control macroscopic properties and can only be captured by examining large areas at fine resolution,” Charpagne said. “The current method for determining the fatigue strength of metals uses traditional mechanical tests, which are costly, time-consuming and do not provide a clear picture of the root cause of failure.”
In the current study, researchers found that statistically examining the nanoscale events that occur during deformation at the metal surface can affect the fatigue strength of metals. The team is the first to reveal this relationship using automated high-resolution digital image correlation collected in the scanning electron microscope — a technique that assembles and compares a series of images taken during deformation, Stinville said. Researchers demonstrated this relationship on aluminum, cobalt, copper, iron, nickel, steel and refractory alloys used in a variety of important engineering applications.
“Notably, the nanoscale strain events that occur after a single strain cycle correlate with fatigue strength, which affects the life of a metal part over a large number of cycles,” Stinville said. “Discovering this correlation is like accessing a unique deformation fingerprint that can help us quickly predict the fatigue life of metal parts.”
“The development of metallic materials with higher fatigue strength means safer, stronger and more durable materials,” said Charpagne. “This work has societal, environmental and economic implications as it sheds light on the micro- and nanoscale parameters to develop materials with longer lifetimes. I think this work will define a new paradigm in alloy design.”
This study was conducted in collaboration with researchers from the University of California, Santa Barbara and the Universite de Poitiers, France.
The Department of Defense, the Office of Naval Research, and the Illinois Department of Materials Science and Engineering supported this research.
Materials provided by University of Illinois at Urbana-Champaign, News Bureau. Originally written by Lois Yoksoulian. Note: Content can be edited for style and length.