In the present paper, criterion of interlaminar strength for unidirectional CFRP laminates was discussed. Generally, interlaminar shear strength (ILSS) of the CFRP laminates is evaluated by 3-point bending test, but the criterion of the fracture depends on not only interlaminar shear stress but also interlaminar normal stress in the specimens. In order to obtain the limit curve which is given by the relation between normal stress and shear stress, two types of ILSS test have been employed in the present study. The one is a 'compression type ILSS test' by a simple 3-point bending. The another one is a 'tension type ILSS test' applying the shear tensile loading using a shear pin. Employing 2-dimensional finite element analysis the criterion of the CFRP laminates and CFRP toughened by carbon nanofiber were investigated in detail using a modified 'Tsai-Wu' criterion.
