Lamina strength unidirectional reinforcement

Figure 2-16 Fundamental Strengths for a Unidirectionally Reinforced 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. 

Determine the allowable stress for uniaxial off-axis loading of the unidirectional fiber-reinforced composite lamina, shown in Figure 8.17. Assume that the lamina strength properties Xl, Xf Xp, Xt, and S are known. Use the maximum stress theory of failure. 

The prediction of macromechanical strength properties of a unidirectional fiber-reinforced composite lamina using micromechanics models has met with less success than the elastic moduli predictions of the earlier sections. The structural designer will most likely rely primarily on results from mechanical tests that measure the macromechanical strength properties of the composite lamina directly. Nevertheless, it is instructive to look at the micromechanics model for tensile strength in the fiber direction of a lamina to gain a better understanding of how the composite functions. 

---