Objective   In order to reduce the thermal expansion deformation of the support structure of the missile-borne optical system at service temperature, the carbon fiber reinforced composite with low thermal expansion coefficient in the fiber direction, strong designability and small specific gravity is used to replace titanium alloy as the main material of the support structure, and the composite support structure is designed by optimization. The optimized carbon fiber reinforced composite support structure shall meet the following requirements: (1) The main geometric size and the interface position shall remain unchanged; (2) Under the condition of 50 ℃ temperature rise, the axial thermal expansion deformation is reduced by more than 85% compared to the titanium alloy support structure; (3) The weight is lighter than titanium alloy support structure; (4) The fundamental frequency shall not be lower than the titanium alloy support structure.

  Methods   Firstly, according to the ASTM (American Society for Testing and Materials) E381 standard, the linear thermal expansion coefficients of the carbon fiber reinforced composite along the fiber direction and perpendicular to the fiber direction are measured using a thermal dilatometer (Fig.6) for two kinds of particular layup. On this basis, a thermal expansion simulation model for the composite structures is established in ABAQUS, and the feasibility of the model is validated by comparing with test results. Then, taking the axial thermal expansion deformation as the optimization objective, the Optistruct software is used to optimize the layer shape, layer thickness, and layer sequence step by step for the two-dimensional carbon fiber composite support structure until the axial thermal expansion deformation meets the design requirements. Based on the optimized two-dimensional model, considering the influence of thermal expansion deformation in the thickness direction, a three-dimensional finite element model of the composite support structure is established in ABAQUS to conduct the analyses of thermal expansion, weight and vibration mode.

  Results and Discussions  From the thermal expansion coefficient tests, the linear thermal expansion coefficients of carbon fiber reinforced composites along the fiber direction and perpendicular to the fiber direction are obtained as 1.397×10⁻⁶/℃ and 37.95×10⁻⁶/℃ respectively (Tab.2). The thermal expansion deformation obtained from the simulation (Fig.7-8) for the laminates with three kinds of layup is in good agreement with the test results (Tab.2). It is shown that the established simulation model can effectively predict the thermal expansion deformation of the composite structures. After five optimization iterations, compared to the titanium alloy support structure, the carbon fiber reinforced composite support structure meets the design requirements with 87.8% reduction in the axial thermal expansion deformation within a temperature rise range of 50 ℃ (Fig.13), with 63.2% reduction in the weight and 24.4% increase in the fundamental frequency (Tab.9).

  Conclusions  Compared to titanium alloy, carbon fiber reinforced composite not only has lower density and greater specific stiffness, but also can achieve low thermal expansion deformation in one direction through reasonable design. Therefore, using carbon fiber reinforced composite instead of titanium alloy as the main material for the support structure of missile-borne optical systems can significantly reduce the axial thermal expansion deformation of the support structure through optimal design, while also achieving structural lightweight and improving structural stiffness.