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2002
Conference Paper
Titel
Thermographic material characterization using dissipative effects
Abstract
A new thermal method for nondestructive materials characterization was developed. This method is based on the analysis of mechanically induced thermal effects in the tested material. Cyclic mechanical loading causes a thermoelastic temperature change and a temperature increase due to heat dissipation. The reason for heat dissipation is the internal mechanical damping (hysteresis losses) in the tested material, which can be characteristic for the (sub-)microstructure and materials mechanical properties. For the excitation of the heat dissipation cyclic mechanical loading close to the yield strength of the material was applied and alternatively also high power ultrasonic loading. The resulting temperature change was measured thermographically on the materials surface. A new approach to the analysis of the thermal effects enabled a quantified evaluation of the dissipated heat energy per single mechanical loading cycle. Hence, the mechanical hysteresis area was characterized independent to the thermal boundary conditions. Mathematical modeling of the thermal loss processes on a specimen confirmed the quantified character of the novel heat dissipation analysis independent to the thermal boundary conditions, e.g. geometry of the test object and room temperature fluctuations. The experimental investigations, primarily performed on dog-bone specimens of the titanium alloy Ti-6Al-4V, confirmed the capacity of this thermal method for fatigue damage characterization. Already during the early stages of fatigue characteristic dependency of the thermal parameter to the diminished lifetime was found. Important advantages of the presented thermal method are the locally resolved evaluation of the thermal parameter using infrared camera, the low time consumption of the measurements (few seconds) and the simplicity of the method. Thus, an in-field application on technical components is principally possible.