Experimentelle Bestimmung des transienten Wärmeübergangs zwischen Festkörpern bei dynamischen Lasten

  • Experimental determination of transient heat transfer between solid bodies during dynamic loading

Burghold, Ernst Michael; Kneer, Reinhold (Thesis advisor); Fieback, Tobias (Thesis advisor)

Aachen (2018, 2019)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2018

Abstract

Although all boundary or contact surfaces between two solid surfaces exhibit a certain thermal resistance, it is particularly relevant at mechanical contacts. The reason for this lies in the almost inevitable technical roughness, which limits the true contact area to a fraction of the geometrical one and promotes the occurrence of the resulting temperature jump. Since the influence of this substantial parameter dominates all other factors, the total resistance is -- as a first approximation -- in inverse proportion to the true contact area. Thus, all variables with a positive influence on the area in contact decrease the thermal resistance, like matching topologies or an applied load to enforce the adaption to the specific contact scenario. The latter can also be supported by the material properties, which, in addition, can also enhance the heat flow through each contact spot to achieve the same effect. In the scope of this work, an experimental setup is developed, which, for the first time, allows the investigation of multiple consecutive load cycles in a single experiment and, therefore, eliminating the need for multiple succeeding test runs. The procedure itself relies on the temperature equalisation of two separately tempered specimens, which are first brought into contact and then loaded by a servo-hydraulic material testing system. After data processing, the thermographically recorded transient temperature fields are then used to solve the inverse heat transfer problem on hand, revealing the thermal contact resistance during loading. While the good agreement between the presented experimental data and the findings described in the literature confirm the validity of the overall procedure, it is also shown that existing macroscopic surface structures can be used to (pre-) condition the thermal contact behaviour during the experiment. Since this is mostly neglected in the typically available surface parameters, this finding illustrates the insufficiency of said parameters for anticipating the heat transfer to be expected.

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