Fracture toughness of epoxy-based stepped functionally graded materials reinforced with carbon nanotubes

Abstract

The aim of this work is to investigate the fracture characteristics of the epoxy-based stepped functionally graded materials (FGM) reinforced with carbon nanotubes (CNTs). The effects regarding fracture toughness in mode I were also studied. The specimens were fabricated with three different mass percentages of 0.1, 0.2 and 0.3%. An ultrasonic device was used to disperse the carbon nanotubes to have a uniform mixture without agglomeration of the CNT particles. Using the ASTM standard D-5045, the fracture toughness was obtained in the experiments. Some compact tension specimens were tested in a tensile machine in mode I. Two different notches were investigated to calculate the fracture toughness. For each notch, there were different fracture toughness and fracture forces values. The experiments showed that there is an improvement in the fracture resistance of FGMs and non-graded composite materials by increase in the CNTs content. The materials with the same content of carbon nanotubes do not have the same properties. It is seen that high fracture toughness can be obtained from different CNT content materials in each notch. In fact, the size of the notch affects the results. Comparing the fracture toughness values and fracture forces results showed that there is no specified rule to predict the increase in the fracture characteristics by increasing carbon nanotubes content. Fracture characteristics depend on the important parameters such as the size of the notch, CNTs content and dispersion of the carbon nanotubes.