The purpose of this study is to determine the correct estimation of the mechanical properties of carbon/PEEK composites and its validity has been tested with the alternative materials of the metal-based materials for artificial hip joint.
This study evaluated the mechanical properties according to the temperature of heat treatments for the sizing removal of carbon fiber and the fiber ply orientation.
First, the sizing removal of carbon fiber were conducted at 300℃ for 4 hours and 400℃ for 2 hours respectively. The fractured surface in the specimen of tensile test made from PEEK and epoxy resin was observed by SEM. The fracture surface of the tensile test specimen of the carbon/epoxy composites heat-treated to 400℃ showed that the resin did not adhere nearly in the fiber surface and pull out was observed. It is considered that 400℃ is suitable heat treatment temperature for the sizing removal of the carbon fiber. The mechanical test results represent that there was no significant differences in short beam strength. However, the tensile strength and compressive strength of the carbon/PEEK composites were higher than those of the carbon/epoxy composites in the case of the vacuum bag process. Furthermore, this result indicated that the sizing material did not have a significant effect on the strength of the carbon/PEEK composites.
Second, the specimens for the carbon/PEEK and carbon/epoxy composites were manufactured based on the ASTM standard. The specimens were immersed in distilled water at 37℃ for 100 days and the coefficient of moisture was measured in accordance with Fick's law. Moreover, the fracture energy according to the fiber ply orientation was evaluated in this study. The result exhibited that the coefficient of moisture-absorption of carbon/PEEK composites was the lowest because the interface coherence between the fiber and resin are the strongest. As a result, the fracture energy of the carbon/PEEK composites was superior to the carbon/epoxy composites.
Third, the effect of Carbon/PEEK composites on the tribological properties has been investigated. The unidirectional composites had higher friction coefficients than those multidirectional composites. This was caused by the debonding between the carbon fiber and the PEEK sheet, which was proportional to the contact area between the sliding surface and the carbon fiber. The friction test results showed that there was no significant differences in relation to the fiber ply orientation. However, the friction properties of the carbon/PEEK composites were higher than those of the carbon/epoxy composites. As a result, it seemed that when the carbon/PEEK composites slid in a direction normal to the prepreg lay-up direction, its friction coefficient may be represented a smaller value compared to sliding in a direction parallel to the prepreg lay-up direction. In a case where the speed was 2.5 m/s, the friction coefficient was relatively large for configuration I. The friction surface of the specimen was analyzed using an electron microscope. In all cases, the debonding of the fiber and PEEK could be confirmed.
Finally, it is suggested that a new concept design of the stem and aims to determine the suitability of various carbon/PEEK composite should be designed for artificial hip joints. Shear stress and principal stress tested with alternative materials of the Ti-based stem for artificial hip joints. In addition, FEA is conducted according to the fiber ply orientation and the load condition for carbon/PEEK composites.