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Hygrothermal behavior of composite laminatesComposite materials can absorb moisture and expand in the same way that they expand due to temperature.We can use the same kind of analysis to deal with stresses that arise from both.In this course we will focus on thermal behavior.The effect of temperatures on composite laminates is more pronounced than on metals because of large disparity in coefficient of thermal expansion.

Effect of mismatch

Thermal deformationsIf ply can expand or contract due to hygrothermal effects, only strains, but no stresses.Stress free expansion strain in a unidirectional layer (Fig. 3.2)

Strains and stressesFree strains

Hookes law when total strains are different from free strains.

Interaction between plies0/90/45 laminate

Constraining effect of adjacent laminates

(0/90)s laminateStress-free expansion of layers

Constrained deformation

Residual strains

Residual stresses

Thermal loadsIf a laminate is subjected to temperature change without any loads then the stress and moment resultants should be zero.

Substituting from previous slide for in-plane equation for symmetric laminate

Loads needed to produce same strains without temperatures

Thermal loads for a single isotropic layer

With bending

With Tsai-Pagano Material constantsThermal loads

Thermal material constants

Any checks that we can apply?