Analysis and research on solution method of metal layer stress in fiber metal laminates

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As a new type composite material, fiber metal laminates (FMLs) have been widely applied in the aerospace field. To further develop and apply this new composite material, a stress prediction method for the metal layer in the laminates was examined. Based on the laminate theory, the stress characteristic of each layer material was analyzed under an external load. By studying the classical laminate theory, it was found that the calculation method of the global stiffness matrix fails to satisfy the actual situation of the laminates. The concept of the equivalent stiffness matrix was therefore introduced to modify the solution of stiffness matrix and accurately predict the metal layer stress. The equivalent stiffness matrix was then obtained using the sub-laminate stiffness theory and the energy method. The sub-laminate stiffness method was improved to apply to the orthotropic FMLs, and the energy method was expanded to apply to FMLs from a three-dimensional perspective. Taking 2/1 and 3/2 laminates of FMLs as examples, the metal layer stress was determined using the optical strain method and was predicted by employing the classical laminate theory along with the two correction methods. The effectiveness and advancement of the modified model were confirmed by comparative analysis.