Interlaminar fracture toughness characteristics of hybrid laminates with nonwoven carbon tissue under severe temperature conditions

To investigate the Mode I and Mode II interlaminar fracture toughness characteristics of hybrid laminates with nonwoven carbon tissue under severe temperature conditions, double cantilever beam and end notched flexure tests were conducted. The hybrid laminates were made by interleaving the NWCT-prepreg between the CFRP-prepreg layers. The mean G_IC values of the hybrid specimens at +60℃ and +80℃ were about 19% and 92% higher than those of the carbon fiber reinforced polymer specimens at +60℃ and +80℃, respectively. The mean G_IC values of the hybrid specimens increased due to the carbon short-fibers bridging and breakage by softening of epoxy resin in the nonwoven carbon tissue layer (NWCT) as the temperature rises. The mean G_IIC values of the hybrid specimens at −60℃ to +80℃ were about 171% to 189% higher than those of the CFRP specimens at −60℃ to +80℃, respectively. When the decreasing rate (the mean G_IIC value of the CFRP specimen at +80℃ was about 18% lower than that of the CFRP specimen at room temperature.) of the mean G_IIC values of the CFRP specimens at +80℃ was compared, the decreasing rate (the mean G_IIC value of the hybrid specimen at +80℃ was about 9% lower than that of the hybrid specimen at room temperature.) of the mean G_IIC values of the hybrid specimens at +80℃ slowed down significantly due to the carbon short-fibers bridging, carbon short-fibers breakage and hackles. Consequently, the mean G_IIC values of the hybrid specimens in the range of −60℃ to +80℃ have no significant influence on softening of epoxy resin.