Strength and Failure Theories for an Orthotropic Lamina

FIGURE 9.1 A schematic representation of five possibte modes of failure associated with uniaxiat test specimen (a) fiber microbuckling in shear mode, (b) fiber microbuckting in extensionai mode, (c) fiber/matrix splitting caused by transverse tensile failure, (d) fiber shear failure, and (e) fiber/matrix kink band formation. 

In Section 8.3, the lamina macrostructural elastic moduli have been defined for the principal material directions. The elastic properties are determined experimentally from uniaxial stress states. If these experiments are carried through to failure of the test specimen, then one also obtains the following macromechanical failure strength properties of the lamina defined in principal material coordinates  

Xl = longitudinal tensile strength X[ = longitudinal compressive strength Xj = transverse tensile strength Xj = transverse compressive strength S = shear strength 

One of the simplest failure theories for orthotropic lamina is the maximum stress theory of failure. This theory states, 

Failure of the lamina will occur if any stress component in principal material directions exceeds the corresponding lamina strength value. That is to avoid failure. 

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