Abstract
As a new and innovative processing method for carbon fiber reinforced thermoplastic composites, the In-Mould-Impregnation process (IMI) adopts carbon fibers as a heating element by electrical conduction. During heating of the dry carbon fibers in the production process, temperatures up to over 500°C can occur. However, the surface properties of carbon fibers and sizing may change under such conditions and thus affect the resulting composite. The present study is a practical approach to validate the suitability of sized carbon fibers for the IMI. The influence of a thermal treatment according to the parameters of the IMI-Process on carbon fiber-thermoplastic matrix interfacial adhesion was investigated by means of micromechanical and optical test methods. The experimental results demonstrate that the thermal treatment of carbon fibers causes a reduction of tensile strength of single fibers. It does not show an influence on the micromechanical breaking behavior in a PA 6 composite but the surface tension of carbon fibers changes. The change in surface tension can affect the wettability of the carbon fiber with a thermoplastic matrix.
Highlights
Polyamides (PA) are used in a wide range of applications in different areas such as the automotive sector, aviation, sport textiles and sport utility industries [1,2,3,4]
The weight reduction of the fiber type Toho Tenax HTS 45 shows an ongoing decrease of the weight until the end of the measurement at 600°C, which is a clue that different thermochemical processes take place, which are not completed when the final temperature of 600°C is reached
The suitability of sized carbon fibers for the In-Mould-Impregnation Process was investigated by means of micro-mechanical and analytical methods, like single filament tension (SFTT) to determine the failure probability, single fiber fragmentation tests (SFFT) to determine critical fiber length and the interfacial shear strength (ISS), thermogravimetric analyses to determine the thermal degradation of the fiber sizing and capillary tests to determine the surface tension of the respective carbon fibers
Summary
Polyamides (PA) are used in a wide range of applications in different areas such as the automotive sector, aviation, sport textiles and sport utility industries [1,2,3,4]. The economic production of thermoplastic continuous fiber reinforced composite parts is still challenging due to the requirement and production costs of semi-finished products (like organo sheets). One new and innovative way to omit the production of semi-finished parts and to produce thermoplastic continuous fiber reinforced composites in a one-step process is the IMI [5]. In this process a non-crimp carbon fabric is impregnated with the thermoplastic matrix within the injection mold. To process a PA 6 composite in IMI, a temperature of 280°C for the carbon fibers is needed. The sizing of carbon fibers may change through the expose to elevated temperatures over 500°C and affect the properties of the resulting composites
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