Effect of specimen size on longitudinal strength of unidirectional carbon/epoxy composite laminates (part 2, splitting strength)

The effects of specimen size as well as notch size on longitudinal splitting failure in notched unidirectional carbon/epoxy laminates are examined. For this purpose, static tension tests are performed on thickness dimension (1D), in-plane dimensions (2D) and all the dimensions (3D) scaled notched specimens, respectively. The experimental results show that splitting strength has a tendency to increase by about 5–10% with increasing thickness dimension of a notched specimen. In contrast, splitting strength tends to decrease by about 20% not only with increasing in-plane dimensions but also with increasing all the dimensions, regardless of notch size. It is suggested that the 3D scaling effect in splitting strength of notched specimens is governed by the 2D scaling effect involved, since the 1D scaling effect is smaller. On the basis of these observations, a scale-sensitive notch size effect law is established. It is demonstrated to adequately describe the specimen-size effect as well as the notch-size effect in the longitudinal splitting strength of the unidirectional carbon/epoxy composite laminates. It is also shown that the effective normalized mode I fracture toughness for splitting failure in the unidirectional CFRP laminate can indirectly be evaluated by means of the scale-sensitive notch size effect law and it is close to the fracture mechanics test results in literature.