Material testing is conducted, for example, to determine the exact numerical values that describe the properties of materials, monitor the quality of manufactured components, or rank materials based on a selected property for product development.
Test methods are usually standardized, but despite this, unknown factors are always present in practical testing that, eventually, affect the final result. As the complexity of the material to be tested or the shape or structure of the test specimen increases, the number of these latently affecting factors increases. In addition, the testing event itself can be very challenging to implement, in which case the operator's actions and subjective decisions in the interpretation of the measurement results can cause significant uncertainty in the final result.
“If the unknown factors influencing the tests can be identified, it is possible to improve the reliability and usability of the test methods. In the end, the measured result reflects better the sought characteristic,” Olli Orell states.
Mechanical testing of materials is usually based on measuring the deformation that occurs in the specimen during the test. The deformation is conventionally examined either in detail at precisely selected local points or by measuring the averaged behavior of the test piece over a larger area.
The DIC method can increase the accuracy of testing
Digital Image Correlation (DIC) is a method based on optical imaging that has developed by enormous leaps in the last two decades. It has already established its use in a great variety of different applications. With DIC the deformation field of the entire imaged body can be determined instead of individual local measuring points. In traditional measurements, for example, the deflection of an object is measured at one point, where the tip of the mechanical measuring device is placed. If the entire testing event is recorded with high quality cameras, the same deflection information can be determined afterwards using the DIC method at the selected point from the saved images.
“The difference is that thousands of these virtual 'devices' can actually be created in the same image, and thus we get a completely different understanding of the object’s behavior during the test. At the same time, for example, it can be examined whether the structures used to load the test specimen function as expected during the test. This also enables completely new types of analysis methods, when data describing the behavior of the piece is available almost without limit,” says Orell.
In his doctoral thesis, Olli Orell studied, among other things, the propagation of crack in a polymer/metal composite structures using DIC. He developed suitable methods for crack monitoring based on the deformation field produced by DIC. There have been known challenges in the usual implementation of the methods. The analysis methods developed by Orell help, for example, significantly reduce the inaccuracy caused by the operator's subjective interpretation and improve the usability of the methods in determining essential material properties.
Public defence on Friday 15 March
The doctoral dissertation of M.Sc. (Tech) Olli Orell in the field of Materials Science titled Enriching Mechanical Characterization Methods of Composites and Hybrids with Digital Image Correlation will be publicly examined in the Faculty of Engineering and Natural Sciences on Friday 15 March 2024 at 12 o’clock at Hervanta Campus in the auditorium K1702 of the Konetalo building (Korkeakoulunkatu 6, 33720 Tampere).
The opponents will be Professor Enrico Cestino, Politecnico di Torino, Italy and Aleksi Laakso, PhD, Meyer Turku Oy. The Custos will be associate professor Mikko Kanerva from Tampere University.
The doctoral dissertation is avaiable online.
The public defence can be followed via remote connection.