Scaling of First-Ply Failure and Strength in [+ϑ_n/−ϑ/−ϑ_n/90/90_2n]_s Laminates: Experiments and Predictions

An experimental investigation of first-ply failure and strength was conducted on ply-level scaled carbon/epoxy composite laminates having a stacking sequence of [+ϑ_n/−ϑ/−ϑ_n/90/90_2n]_s where the constraint ply angle, ϑ, was varied from 0 to 75°, and where the constraint ply angle, ϑ, was varied from 0 to 75°, and n varied from 1 to 4. First-ply failure was shown to depend on the level of constraint and the scale factor, n. The strain energy release rate for matrix microcracking was computed from first-ply failure data of the [0₂/90₂]_s laminate. Then, first-ply failure for all other layups was predicted using a numerical model that accounted for both constraint and size. Tensile strength was predicted using a strain energy release rate model for delamination of surface angle plies. A delamination energy value for each ply angle was calculated from the thinnest (n = 1) laminates to predict strength of the other sizes.