Impact of hygrothermal environment on the bistability of variable stiffness laminates with curvilinear fibre paths

Moisture absorption in composite materials has significant importance in the analysis and design of structural components, which fully depends on the surrounding environment. Stress field created by moisture absorption is similar to the one created by thermal stresses during the curing stage. The additional stresses generated can cause a curvature reduction and ultimately the relaxation of actuation energy required for crossing the energy barrier between stable shapes. This paper aims to examine the impact of hygrothermal environment on the bistability of variable stiffness composite shells with curvilinear fibre paths. Rayleigh-Ritz method-based semi-analytical formulation is extended in the present analysis. Validation of the semi-analytical formulation is subsequently done using an appropriate numerical model simulated in a commercially available finite element package. Numerical model created in a finite element platform usually does not include hygrothermal effects in the basic constitutive formulations. To overcome this problem, thermal properties are revised to include the hygrothermal effects. A systematic procedure for the same using the hygrothermoelastic constitutive equations is used for the analysis. The importance of hygrothermal effects on the bistability is observed from the systematic study as it is crucial for the true evaluation of the performance of bistable variable stiffness laminates.