An Experimental Investigation into the Damage Mechanisms in Notched CCF300/QY8911 and T300/QY8911 Composites Subjected to Hygrothermal Environment Condition

An experimental study was carried out to determine the notched tension characteristics of CCF300 fiber reinforced composite and T300 fiber reinforced composite subjected to normal and hygrothermal environment conditions. First, tests to failure with residual strength were carried out and the damage progressions were carefully investigated. Scanning electron microscope (SEM) was then employed for fractographic investigations. It was found that the CCF300/QY8911 composite specimens with poor interfacial adhesion between fiber and matrix exhibited higher residual strength, while the T300/QY8911 composite specimens with well adhesion had shorter ultimate strain. Damage progression mechanisms in the two material systems were very different. The major damage mechanism of CCF300/QY8911 composites was delamination generally occurring at lower stresses, which allowed higher levels of damage formation and resulted in higher ultimate strength. When changing to hygrothermal environment condition, greater damage was observed and off axis plies were extensively pulled out from the adjacent plies. On the other hand, all of the T300/QY8911 composite specimens failed due to fiber fracture with less damage, leading to a lower residual strength regardless of the environmental conditions. Further examinations showed that the failure mode of CCF300/QY8911 composite was much more sensitive to the hygrothermal environment, for the micro-failure mode had changed from matrix failure and fiber breakage to fiber/matrix splitting and fiber bundle pullout.