Laminate design unidirectional composite laminae

The material presented in Ch ters 8 and 9 should provide the reader with the fundamentals needed to understand the performance characteristics of composite materials and lamina, and laminates used in the design of engineering structures. The presentation concentrates on the mechanics of a unidirectional composite lamina, with emphasis on its elastic and strength response. A brief development of the micromechanics of a lamina is also presented to provide a basis for understanding how constituent material elastic and strength properties of the fiber and resin contribute to the maaoscopic response of the lamina. 

Fibers are often regarded as the dominant constituents in a fiber-reinforced composite material. However, simple micromechanics analysis described in Section 7.3.5, Importance of Constituents, leads to the conclusion that fibers dominate only the fiber-direction modulus of a unidirectionally reinforced lamina. Of course, lamina properties in that direction have the potential to contribute the most to the strength and stiffness of a laminate. Thus, the fibers do play the dominant role in a properly designed laminate. Such a laminate must have fibers oriented in the various directions necessary to resist all possible loads. 

Most unidirectional composites are manufactured from prepreged layers of yarns. Each layer is called a lamina and a group of lamina is called a laminate. Each lamina in the laminate can have a specific direction based on the design requirements starting from an arbitrary direction. The only important matter to remember is that these laminates must have a mirror symmetry around their neutral axis otherwise they will warp immediately after manufacture and cannot be straightened. This happens due to the difference in the thermal expansion coefficients between the fibers and the matrix and between different lamina causing one side to permanently expand more than... 

The influence of the orientation of the laminae on the stiffness of the composite is illustrated in Figure 15.15b, where generic stress-strain curves for unidirectional cross-ply random laminates are shown. In the design of laminates it is necessary to define not only the orientation of the plies but also the stacking sequence, i.e., the order in which the plies are placed through the thickness. Figure 15.16 shows examples of symmetrical and non-symmetrical laminates. The most standard ply orientations are 0°,... 

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