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DoITPoMS Teaching & Learning Packages Mechanics of Fibre-reinforced Composites Tensile–shear interactions and balanced laminates

# Tensile–shear interactions and balanced laminates

From equation 15, the 'interaction' terms S16 and S26 are both non-zero and this indicates that, under off-axis loading, normal stresses produce shear strains (as well as normal strains) and shear stresses produce normal strains (as well as shear strains). This tensile-shear interaction is also present in laminates, but does not occur if the loading system is applied along the principal axes of a single isolated lamina, in which case S16 = S26 = 0 as in equation 13.

${\eta _{xyx}} = {E_x}{\overline S _{16}}\;\; and\;\;{\eta _{xyy}} = {E_y}{\overline S _{26}}$

The extent of this tensile-shear interaction is quantified by the parameters ηxyx and ηxyy (Click to open pop-up)

### Balanced laminates

Tensile-shear interactions are undesirable as they lead to distortions and local microstructural damage and failure. A laminate whose interaction ratios are zero is said to be 'balanced' . Use the model below to investigate the variation of ηxyx with loading angle.