A research team at Worcester Polytechnic Institute (WPI) in the U.S. is expanding its understanding of how stress and fatigue cause microscopic damage to form in metal components.

Funding for this research comes from the U.S. Army Research Office through the Defense University Research Instrumentation Program (DURIP). While the Army has awarded $239,000 for this work, industry has also supplied an additional $60,000.

Diana Lados, founding director of the university's Integrative Materials Design Center (iMdc) and her team will conduct comprehensive testing and characterization studies to understand and monitor how tiny cracks are initiated and then grow in metal components as they are subjected to repetitive (or cyclic) strains and stresses similar to those that wings, fuselages, and other aircraft components experience in service. Using a new imaging system, the researchers are able to view the initiation and propagation of cracks at the micro-scale while metal samples are stressed in a servo-hydraulic testing machine. These fatigue cracks can be detected both at the surface of metal samples and also by using electromagnetic induction, within the metal microstructure.

‘What we will learn is how the microstructures of these materials influence crack initiation and growth phenomena,’ said Anthony Spangenberger, a PhD candidate who joined the iMdc team in 2012. ‘We can identify damage hot spots in the microstructure that will help us better engineer our materials for optimized structural performance.’

With the knowledge gained through laboratory testing, advanced characterization, and computational modelling, the team is looking to develop new lightweight metal alloys that are more resistant to cracking, or in which small cracks are less likely to expand into larger fissures that would require a component to be repaired or replaced. In addition, they hope to be able to develop algorithms that will make it possible to predict, based on the state of stress and the rate of crack progression in a component, when servicing will be required.

‘By understanding the behavior of the materials, we can swap out heavier steel components for lighter aluminum alloys, which are going to behave reliably because we will design better for fatigue and crack growth resistance under different operating conditions,’ said Spangenberger.

Critical components

Lados said the technology she and her team are using in the lab can be incorporated into sensors that could be attached to critical components in airplanes to detect and monitor fatigue damage in real time. Currently, she said, aircraft are taken out of service at set intervals to be inspected for fatigue-related cracking. By monitoring aircraft components continuously, and employing the predictive algorithms being developed in the Lados lab, it may be possible to schedule aircraft servicing only when needed, which could significantly reduce costs and out-of-service time.

‘This technology, with its multiple uses, would bring important advancements to the materials and aircraft industries, contribute to increased safety and on-time performance, and undoubtedly save time and money for aircraft operators and, ultimately, the airlines,’ said Lados. ‘I think this research will go a long way to enhancing the way the aircraft industry views its inspection and monitoring systems.’

This story is reprinted from material from Worcester Polytechnic Institute, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.