Objective   Infrared calibrators directly determine the detection accuracy of infrared devices as the reference standard for radiation measurement of infrared devices before the satellite launching. More precise infrared calibrators with large surface are required with the development of infrared optical satellites characterized by large aperture, large field of view and high precision, which means the structure of infrared calibrators must keep stable in high and low temperatures to guarantee the high temperature uniformity of the radiant surface, high precision of temperature control and high stability of the system. In the calibration test, the structure thermal mismatch easily occurs because the multilayered structure of infrared calibrators connected with bolts usually includes a variety of different materials and the deformations become unmatched during heating and cooling process for different thermal expansivity, which can reduce the calibration accuracy and increase security risks and test cost. As a result, optimal design and verification of thermal adaptive structure for the infrared calibrator with large surface, wide temperature range and multiple materials were carried out, to solve the problems caused by structure thermal mismatch, including the loose bolts, low cooling rate and bad thermal uniformity at the low temperatures, as well as the compression failure of heat insulating mattress made of glass reinforced plastic at the high temperatures.

  Methods   From the two aspects of normal preload regulation and in-plane warping deformation control, the key materials were selected, the assembly parameters were adjusted and the structure parameters were optimized. Simulation analysis and tests were combined to explore the change rules of bolts preload on multilayered structure made of different materials when the temperature changed, at the same time verify the safety and stability of the structure. Finally, the key technical indexes of infrared calibrator were verified by means of heating and cooling tests.

  Results and Discussions   The calculations based on the linear elastic theory indicated that the change of preload was controlled effectively by means of choosing Teflon as heat insulation material and stainless steel as bolt material (Tab.1), which provided a smaller relative deformation between bolts and connected members caused by the temperature change. The original preload was applied between 12 N·m to 20 N·m to avoid bolts looseness at −100 ℃ and deformation failure at 140 ℃ (Tab.2). Furthermore, the diameters of mounting holes were enlarged to be greater than 25 mm to reduce the in-plane warping deformation resulting from bolts shearing (Tab.3). The tightening torque test based on multilayered structure composed of different materials discovered the rules that the tightening torque got linear relation with the deformation in the certain range. The elastic deformation occurred at the low temperatures and on the other hand the plastic deformation was more likely to occur at the high temperatures. The axial stiffness of multilayered structure could be improved by repeating heating and cooling process (Fig.4). The simulation result of the whole system suggested that the proportion of bolts with safe and effective connections had reached more than 90% under the high and low temperatures (Tab.3). The stress of bolts at the upper and lower edges of the calibrator changed more significantly than that at other positions and therefore different assembly parameters could be set according to the bolt positions. The heating and cooling test of infrared calibrator showed that the structure was safe and stable with the temperature change, the cooling time was shortened from 30 h to 4 h (Fig.7), and the temperature deviation of the radiant surface at 193 K was improved from −0.8 K/+0.9 K to −0.3 K/+0.4 K.

  Conclusions   The optimal design of thermal adaptive structure can significantly increase the cooling rate of infrared calibrator and improve the thermal uniformity of radiant surface at the low temperatures. The difficulties of loose bolts at the low temperatures and compression failure of heat insulating mattress at the high temperatures were overcome at the same time. This study solved the practical problems in the calibration test and the structural safety and stability after optimal design can meet the design requirements. The optimal design methods of thermal adaptive structure can be referred for the same type of products.