As the application areas of textile composite materials are steadily being expanded in the areas such as aerospace or military sectors, it is essential to develop the technology for their fabrication process and the evaluation methods of mechanical properties. Among many types of textile composites, the braided carbon fiber reinforced metal matrix composites have been considered as a candidate material for automobiles and structural materials because of high specific strength, high specific modulus and high temperature stability.
In this study, two-dimensional(2-D) triaxial braided preforms with braiding angles of 30, 45 and 60 were manufactured by using a braiding machine. And then the 2-D triaxial braided carbon fibers were used as reinforcement to manufacture aluminum matrix composites by employing a pressure infiltration casting method, and their mechanical properties were evaluated. In the processing of pressure infiltration casting, important processing parameters involved melting temperature, preheating temperature of preform and applied pressure. It was found from the experiments that two former parameters were closely related to pressing timing. In order to optimize the process parameters, the analysis of cooling curve of the melt on braided preform and the calculation of theoretical infiltration pressure was carried out. After pouring liquid aluminum into the mold, the solidified layers were generated both in the surface area of liquid aluminum and in the contact area between mold and liquid aluminum. This solidification process considerably influenced the time to apply pressure. The analysis was performed on the determination of this pressing time. Loss of applied pressure occurred owing to plastic deformation of solidified layers generated between mold and liquid aluminum during pressure infiltration casting method. Therefore, it was inevitable to select the higher pressure i.e., 60MPa, than theoretical value of 1MPa.
The current thesis is also focused on the theoretical prediction and the mechanical properties of the manufactured braided carbon fiber/Al metal matrix composites. Prediction of mechanical properties on composites must be managed. Thus, volume averaging method was used to predict the geometric characteristics and the elastic modulus of the composites. Also, prediction of tensile strength values was concluded by using the bridging method. The elastic moduli of composites were evaluated by using static tensile test method and RUS(Resonant Ultrasound Spectroscopy). The elastic moduli measured experimentally were compared with the calculated values obtained by the volume averaging method. In addition, the tensile strengths of the composites were evaluated through the tensile test. However, It was shown that the lower tensile strength values than predicted values were obtained. It may be due to CTE(coefficient of thermal expansion) mismatchs or the formation of interfacial reactants produced between aluminum and carbon fiber during the fabricating process.
From the results of this study, the relationships among the parameters on fabrication process, the microstructures, the mechanical properties of braided carbon fiber/Al MMCs were constructed. Based on these results, the theoretical calculation of the braided carbon fiber/Al MMCs were obtained, which could predict their mechanical properties adequately.
Hereby, it is expected that the fabrication process and the evaluation methods if mechanical properties on the braided carbon fiber/Al metal matrix composites are established and their application field is expanded.
