Influence of Layer Thickness on the Strength of Angle-Ply Laminates

Experimental results are presented showing that the strength and toughness of finite-width angle-ply laminates can be increased significantly by using an alternating layer stacking sequence as opposed to a clustered con figuration. The ultimate tensile stress of an alternating plus/minus θ laminate of the form [(±θ)2] s can be as much as 1.5 times that a clustered configura tion of the form [θ2/—θ2] s . Further, the toughness of the alternating layer configuration can be as much as 2.7 times that of the clustered configuration. These differences are explained analytically through consideration of the in fluence of layer thickness on the magnitude of the interlaminare shear stress and by examination of failed specimens. It is shown that the two laminate configurations exhibit distinctly different failure modes for some fiber angles. Both laminate configurations exhibit catastrophic failure with the damage limited essentially to a small region defined by the length of a single crack across the face of the specimen, parallel to the fiber direction. Results are presented for T300/5208 graphite-epoxy for fiber orientations of 10°, 30 °, and 45 °.