Analysis of strain uniformities in asymmetric bistable composite laminates

Asymmetric composite laminates can have a bi-stable response, due to during the elevated temperature of manufacturing process, and residual thermal stresses lead to a curved shape at room temperature. These laminates can have two stable configurations at room temperature: cylindrical configuration I with a major curvature in x axis and cylindrical configuration II with an opposite curvature in orthogonal y axis. The large deflections that can be achieved by snap-through from one configuration to another, along with a need for small and removable energy input, make them of interest for a wide range of engineering application, notably morphing application in the aerospace industry. After 30 years of research efforts the shapes and response of asymmetric laminates of general layup have been well characterized. In this work, the Extended Classed Lamination Theory is considered as a basic approach to analysis the strains distribution of the bi-stable laminates. The paper begins by outlining the existing modeling formulation for arbitrary layup laminates and deriving an analytical formulation to an orthogonal laminate geometry. It is found that the distributions of strains are uniform, and the magnitudes of strains are closely related to the configurations. The strain of x direction is much more than y direction in configuration A with a major curvature in x axis. The similar situation also exists in configuration B. The changes of strains during snap-though are discussed, and compared with the Finite Element Models and experiments. The strain gauge test is carried out in experiments. The results show that the distributions of Models and experiments. The strain gauge test is carried out in experiments. The results show that the distributions of strain changes are also even.