Effect of lay-up sequences on mechanical properties and fracture behavior of CFRP laminate composites

A long carbon fiber with 3.5 GPa in average tensile strength-reinforced epoxy plastic (CFRP) laminates has been studied to determine the effect of the lay-up sequences on the mechanical properties and fracture behavior of the advanced carbon fiber-reinforced plastics (CFRP) composite. The mechanical properties were evaluated by tensile, slow bend and instrumented Charpy impact tests. Specimens with angles of 0°, 45° and 90° between the fibers of the 0° layers and the longitudinal direction of the specimen ((0°), (45°) and (90°) specimens) were used. The unidirectional laminate (0°/0° ply-(0°)) specimen exhibited high slow bend and Charpy impact fracture energy values as well as high strength, but they had a remarkable anisotropy for the mechanical properties. The orthotropic laminates (0°/90° plies) had improved anisotropy for the properties compared with the 0°/0° ply-(0°) specimen. However, the tensile fracture stress of the 0°/90° ply-(0°) and (90°) specimens were about one-half that of the 0°/0° ply-(0°) specimen and their slow bend and Charpy impact energies were about one-third those of the 0°/0° ply-(0°) specimen. Although the tensile fracture stress of the 0°/90° ply-(45°) specimen significantly decreased, its slow bend and Charpy impact energies drastically increased. There was a significant benefit in the mechanical isotropy for the quasi-isotropic laminates (0°/90°/±45° plies). However, their mechanical properties were about 40% of that of the 0°/0° ply-(0°) specimen. These results are described and discussed.