Theoretical and Measured Cross-Ply Laminate Stiffnesses

Two- and three-layered special cross-ply laminates were shown to have extrema of behavior in the preceding section. Thus, comparisons between theoretical and measured stiffnesses for such laminates should 

The individual laminae used by Tsai [4-6] consist of unidirectional glass fibers in a resin matrix (U.S. Polymeric Co. E-787-NUF) with moduli given in Table 2-3. A series of special cross-ply laminates was constructed with M = 1,2,3,10 for two-layered laminates and M = 1,2,5,10 for three-layered laminates. The laminates were subjected to axial loads and bending moments whereupon surface strains were measured. Accordingly, the stiffness relations as strains and curvatures in terms of forces and moments, that is. 

The experiments were performed on two sets of beams with the beam axis at 0 and 90°, respectively, to the fiber direction of the odd-numbered layers. The beams were 1-in (25.4-mm) wide,. 12-in (3-mm) thick, and of 6-in (152-mm) span. Strain rosettes were located on the upper and lower beam surfaces so that the middle-surface strains and curvatures can be calculated from simultaneous solution of 

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