Training Module #8: Composites - A Closer Look at Composite Materials

Ply-based failure analysis is the traditional approach to composite analysis where the failure of a laminate is determined whenever any ply reaches its allowable material limit as defined on the Composite Material. The various ply-based failure theories available in HyperX are tabulated below. Note that there are three main categories of ply-based failure: fundamental, quadratic, and physics-based.

Laminate-based failure theories quantify the failure of an overall laminate rather than the failure of an individual ply.

Overall laminate strains are compared with laminate strain allowables. For a given laminate, the laminate strains (\(\varepsilon_x\), \(\varepsilon_y\), \(\gamma_{xy}\)) are transformed in four orientations (\(\varepsilon_0\), \(\varepsilon_{+45}\), \(\varepsilon_{-45}\), \(\varepsilon_{90}\)) to get four margins of safety for each analysis. In cases of laminate bending, laminate margins are computed at both the top and bottom surfaces.

The laminate allowables are defined as a function of ply percentages in the Orthotropic Material Form. Ply percentages can be expressed as percent 0° fibers (%0), percent ±45° fibers (%45), Angle Minus Load (AML = %45 - %0), as a general polynomial, or as 1/Kt-1/3 values. In addition, laminate allowables can also have Correction Factors for thickness or sandwich co-cure.