The rapid deformation of a car during a crash and the elevated temperatures during atmospheric re-entry of a spacecraft are examples of extreme conditions experienced by some engineering applications. In designing and developing of applications, it is important to understand how materials behave under the conditions they are designed to withstand.
“Investigating how material behaves under load is a common task for engineers and material scientists but it gets considerably more complex when using purely traditional testing techniques at higher speeds and temperatures. The use of novel high-speed optical and infrared imaging for monitoring a mechanical test makes it possible for much more information on the behaviour of materials under different conditions to be acquired,” says Soares.
Analysing the behaviour of materials using optical and infrared cameras is not completely straightforward, even when dealing with low-speed tests at room temperature. The difficulty increases considerably with when monitoring events that occur at higher strain rates or temperatures, which can take tens or hundreds of microseconds and/or the sample can be over thousand degrees Celsius and close to its melting point.
In his dissertation work, Soares developed a research method that combines mechanical testing (i.e., measuring the applied on a material) with deformation measurements made with optical cameras, and temperature measurements of the heat release caused by the plastic work with an infrared camera. His work also presented solutions for the for synchronous data acquisition in experiments that only lasted microseconds, representing data from multiple high-speed cameras in the same coordinate system, and calibrating the measurements of an infrared camera to actual surface temperature.
Imaging offers solution to investigate materials in extreme conditions
The results of Soares’s work show a comparison of the evolution of strains and temperature of several different metals and alloys, tested under tension and compression at a wide range of strain rates and temperatures up to 1350 °C. Given the sheer amount of data that is acquired in each test, the results were difficult to present in a comprehensible format. For this reason, Soares developed different graphical representations to visualize the relationship between the mechanical behaviour, temperature, deformation, and strain rate of a material.
“My results showed that imaging techniques are a powerful tool to investigate material behaviour and provided information on the behaviour of materials which would not have been accessible with only traditional testing methods. This data can be used to improve and validate current material models and help orientate future product design in the industrial sector,” Soares concludes.
The Doctoral Dissertation of M. Sc. Guilherme Corrêa Soares in the field of Materials Science titled Thermomechanical Behaviour of Materials under Extreme Conditions Studied with High-Speed Optical and Infrared Imaging will be publicly examined in the Faculty of Engineering and Natural Sciences at Tampere University at 12 o’clock on Friday 22.04.2022 at Korkeakoulunkatu 6 in the auditorium K1702 of the Konetalo Building. The Opponent will be Professor Pascal Forquin from University of Grenoble and Dr Stephen Walley from University of Cambridge. The Custos will be Professor Mikko Hokka from the Faculty of Engineering and Natural Sciences.
The dissertation can be found online at http://urn.fi/URN:ISBN:978-952-03-2362-2.
Photo: Annso Rudolph