An efficient testing method to determine the anisotropic thermal conductivity of long-fiber reinforced composites
Topic(s) : Experimental techniques
Co-authors :
Julian M. KARSTEN (GERMANY), Farida TOUNI (GERMANY), Bodo FIEDLER (GERMANY)Abstract :
Efficient thermal management strategies are becoming increasingly important in modern fiber composite applications. Whether for systematic heat dissipation for highly integrated electrical devices or for thermal insulation from adjacent heat sources. The directional anisotropy of the thermal conductivity of continuous fiber reinforced composites allows for efficient heat dissipation in the fiber direction and effective thermal insulation perpendicular to the fibers. By adding thermally conductive fillers, such as graphene or carbon nanotubes (CNTs) to the polymer matrix, the conductivity can also be tailored to specific requirements. However, few experimental studies have been conducted on the anisotropic heat transfer properties of fiber-reinforced composites.
This paper presents a efficient test method for characterizing the anisotropy of the thermal conductivity of continuous long fiber reinforced composites. The primary objective is to provide a cost- and labor-effective test for anisotropic materials compared to conventional approaches that are typically designed for isotropic materials.
As part of this approach, the thermal properties of carbon fiber composites with different fiber orientations are being evaluated. First, DSC measurements are carried out to determine the heat capacity of the materials under investigation.
The thermal conductivity is determined by a transient time-temperature measurement method using a test rig consisting of a heater cartridge as the main central heat source and systematically distributed negative temperature coefficient thermistors (NTCs) along a specific measurement angle (0° ≤ phi ≤ 90° and delta = 15°) with respect to the unidirectional plate test specimen. A graphical user interface allows for the configuration of the measurement setup in Python, a live display of the measurement results and subsequent automated evaluation.
In addition, thermographic measurements are carried out, which are based on the layout of the newly developed test stand and can be used as an alternative measurement method for data acquisition. Additionally, this method allows the determination of thermal conductivity for arbitrarily small angles. Both methods proved effective in this study.
For a better classification of the results, a visual comparison was made with other isotropic standard materials and the results were plotted in an Ashby diagram, see Figure 1.
For later validation of the measurement system and data processing, the thermal conductivity is also measured using xenon flash analysis (XFA) as an overall reference, which shows a good agreement as seen in Figure 2.
This paper presents a efficient test method for characterizing the anisotropy of the thermal conductivity of continuous long fiber reinforced composites. The primary objective is to provide a cost- and labor-effective test for anisotropic materials compared to conventional approaches that are typically designed for isotropic materials.
As part of this approach, the thermal properties of carbon fiber composites with different fiber orientations are being evaluated. First, DSC measurements are carried out to determine the heat capacity of the materials under investigation.
The thermal conductivity is determined by a transient time-temperature measurement method using a test rig consisting of a heater cartridge as the main central heat source and systematically distributed negative temperature coefficient thermistors (NTCs) along a specific measurement angle (0° ≤ phi ≤ 90° and delta = 15°) with respect to the unidirectional plate test specimen. A graphical user interface allows for the configuration of the measurement setup in Python, a live display of the measurement results and subsequent automated evaluation.
In addition, thermographic measurements are carried out, which are based on the layout of the newly developed test stand and can be used as an alternative measurement method for data acquisition. Additionally, this method allows the determination of thermal conductivity for arbitrarily small angles. Both methods proved effective in this study.
For a better classification of the results, a visual comparison was made with other isotropic standard materials and the results were plotted in an Ashby diagram, see Figure 1.
For later validation of the measurement system and data processing, the thermal conductivity is also measured using xenon flash analysis (XFA) as an overall reference, which shows a good agreement as seen in Figure 2.