Boundary Layer Transient Hygroscopic Stresses in Orthotropic Thick Shells Under External Pressure

An exact elasticity solution is obtained for the stresses and displacements in an orthotropic cylindrical shell loaded by an external pressure under imposed constant moisture concentrations on the inner and outer surfaces. The material properties are assumed moisture independent and a displacement approach is used. Since the moisture diffusion process is relatively slow, the hygroscopic stresses are confined for practical time values to a boundary layer region near the surfaces. Illustrative results are presented for graphite-epoxy material regarding the boundary layer hygroscopic effect on the stress field with respect to time and the coupling of mechanical loading (external pressure) and moisture diffusion. For this material, it is shown that this effect is more pronounced for the axial component of stress.