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6.8: Tensile–Shear Interactions and Balanced Laminates

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    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.

    \[\eta_{x y x}=E_{x} \bar{S}_{16} \text { and } \eta_{x y y}=E_{y} \bar{S}_{26}\]

    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.

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