Investigation of Thermal Effects in Cyclic Loaded Metallic Materials

The progress in the development of thermographic cameras has raised the interest of investigating thermal effects during mechanical loading of metallic materials. An elastic deformation causes the well-known thermoelastic effect, which depends on the elastic loading amplitude. A non-elastic deformation causes the dissipation of energy and leads to an increasing specimen temperature. These thermal effects can be used to determine mechanical properties of metallic materials and to gather information about the deformation state of cyclic loaded components.

Using the thermoelastic effect, the sum of the stress amplitudes in cyclic loaded components can be determined. The dissipated energies give information about the plastic deformation. To quantify these effects, the measured temperature signal has to be divided into these two individual parts. This is normally undertaken with the so-called Lock-In thermography where the signal is decomposed using a discrete Fourier transformation (DFT). The thermal signal oscillating with the loading frequency is attributed to the thermoelastic effect; the part oscillating with the double loading frequency is assigned to dissipative effects. Newer investigations have shown, that this simple decomposition of the signal does not reflect the true material behaviour.

In this work, the Lock-In thermography of cyclic loaded metallic materials will be introduced. Beside the theory, some examples for the investigation of cyclic loaded parts and in the field of fatigue crack propagation will be presented. The possibilities and limitations of this method will be discussed and some future trends for the evaluation of thermographic measurements on cyclic loaded components will be given.

PD Dr. J. Bär

Institute for Materials Science

Bundeswehr University Munich

Werner-Heisenberg-Weg 39
85579 Neubiberg

Phone	+49 89 6004 2561
Email	PD J.Bär
Http	PD J. Bär
	Institute for Materials Science
	Bundeswehr University Munich