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

Abstract

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 fiber direction to about 10 off-axis direction, but it turns to decrease monotonically as the off-axis angle increases further in the range up to 90 . 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.

The effect of microfibrils cellulose modified epoxy on the quasi-static and fatigue behaviour of open hole carbon textile composites

“…The strength and the failure mechanisms of notched composite materials were extensively investigated over the past three decades due to its importance in several industrial applications where joints and bolts are unavoidable. 1 Several investigations were dedicated to the coupling of notch sensitivity and fatigue performance, 2–4 being the main concern in composite material applications involving repeated loading cycles.…”