Failure of fiber reinforced orthotropic layers. Failure often controlled by the complex interaction of fibers and matrix. Still, the ideal was to come up with failure criteria that are small generalization of those used for isotropic materials. (a,b) fiber microbuckling; (c) kink band; (d) shear failure on 45-deg plane.

How many experiments?

Max stress and max strain criteria Max stress (note that these are no longer principal stresses) Max strain

Example 6.2.1

Solution procedure

Tensile strength

Comparing tensile to compressive strength What changed about the envelope?

Biaxial loading Anything remarkable?

Tsai-Hill Criterion

Hoffman criterion Oscar Hoffman, Lockheed 1967 To account for difference in tension and compression need to have linear terms Derivation as homework. Criterion is no longer homogeneous. What does that mean? Implication for safety factors. Have a paper on that with A. Groenwold of U. Stellenbosch.