Anisotropic size effect law for notched strength of unidirectional carbon/epoxy laminates - Part 2: Comparison with experiment

The multiaxial quasi-brittle failure criterion for notched orthotropic composites that was formulated in the first part of this study is evaluated on the basis of the off-axis notched strength of a unidirectional carbon/epoxy composite. Static tension tests are first carried out on center circular hole specimens of different hole diameters and fiber orientations to examine the notch size effect as well as the fiber orientation effect on the off-axis notched strength of the unidirectional composite. Experimental results show that the tensile strength in the fiber direction is more notch-sensitive than that in the transverse direction. The notch sensitivity in off-axis strength increases as the off-axis angle increases from the 0 degrees fiber direction to about 10 degrees off-axis direction, but it turns to decrease monotonically as the off-axis angle increases further in the range up to 90 degrees. Then, the analytical formulas to predict the off-axis notched strength, off-axis notch sensitivity, off-axis intrinsic equivalent mode-I fracture toughness, and off-axis apparent equivalent mode-I fracture toughness of unidirectional composites are established on the basis of the multiaxial quasi-brittle failure criterion. These analytical formulas succeed in efficiently predicting both the effects of notch size and fiber orientation on the off-axis notched strength of the unidirectional composite. It is also shown that the intrinsic and apparent off-axis equivalent mode-I fracture toughness values predicted for brittle failure and quasi-brittle failure, respectively, correlate well with the experimental results.