Effect of specimen size on longitudinal strength of unidirectional carbon/epoxy composite laminates (part 1, unnotched strength)

The effect of specimen size on tensile strength of a unidirectional carbon/epoxy laminate in the longitudinal direction is examined. For this purpose, static tension tests are performed on thickness dimension (1D), in-plane dimensions (2D), and all the dimensions (3D) scaled specimens, respectively. The experimental results show that the tensile strength has a tendency to decrease by about 40–60% with increasing thickness dimension by a factor of 2. In contrast, the tensile strength tends to increase by about 60–130% with increasing in-plane dimensions by a factor of 2. The tensile strength has a tendency to slightly increase by about 6% with increasing all the dimensions by a factor of 2. The effect of 1D scaling on the tensile strength is opposite to that of 2D scaling, and the 2D scaling effect is slightly more significant than the 1D scaling effect. The 2D scaling effect in the tensile strength masks the 1D scaling effect when they are involved at the same time. The latter is consistent with the small 3D scaling effect that is similar in nature to the 2D scaling effect. On the basis of these observations, a phenomenological equation to describe the effect of specimen size on the tensile strength of the unidirectional carbon/epoxy composite is established. It is demonstrated that the scale effect model can adequately describe the 1D, 2D, and 3D scaling effects on the tensile strength of the unidirectional composite.