Design And Fabrication Of Flexible Thin Film Thermocouples For Transient Temperature Measurement Of Warhead Surface

In missile target shooting or wind tunnel test,it is necessary to accurately test the transient temperature of the warhead surface.However,due to the characteristics of fast flight speed,large volume and curved surface of the warhead,the commonly used temperature measurement techniques,such as integrated thin-film thermocouples and armored thermocouples,are difficult to accurately measure the surface temperature of the warheads.Flexible thin-film thermocouples are one of the reliable technologies for transient temperature measurements of the warhead surfaces.Therefore,the thesis focused on the design,preparation and calibration of flexible thin-film thermocouples,the main content are as follows:Firstly,based on Comsol finite element simulation,the influence of the laser parameters on the dynamic response time measurement and the influence of the structure of thin-film thermocouple thermal junction on the response time of thin-film thermocouple were explored.The structure of the thermal junction were optimized in order to reach the peak signal before the sensor is destroyed.The simulation results show that when the beam completely covers the thermal junction,the pulse energy has no effect on the results of the response time measurement.The response time decreases with the decrease of film thickness of the thermal junction,and it is independent of the area of the thermal junction.Secondly,a multi-point NiCr/NiCu flexible thin-film thermocouple was designed using the common-pole method.NiCr was used as the common electrode,the thermocouple size was 95 mm×6.1 mm×0.2μm,and the line width was 1 mm.A polyimide tape with a thickness of 0.1 mm and an alumina ceramic substrate were selected as the substrates,and NiCr/NiCu thin film thermocouple was fabricated by magnetron sputtering combined with mask patterning.The thermoelectric properties of the prepared thin-film thermocouple were calibrated.The results showed that the average Seebeck coefficient of the sample was 64.48μV/℃in the temperature range of100℃～800℃,and the sample’s average Seebeck coefficient in the low temperature range of-80℃～100℃.The average Seebeck coefficient is 64.07μV/℃,and the sample has good linearity in the temperature range of-80℃～800℃;The response time of the thin-film thermocouple was calibrated by a pulsed laser calibration system.The results show that the variation of the response time with different thermal junction thicknesses is consistent with the finite element simulation results.When the thickness of the NiCr/NiCu thermal junction is 200 nm/200 nm,the response time is as fast as 15.88μs.Finally,the flexible NiCr/NiCu thin film thermocouple was attached to the surface of the cylinder with different radii,and the static thermoelectric performance was tested in the temperature range of-80℃～100℃.Under the condition that the maximum bending curvature is 1 cm^-1,the average Seebeck coefficient of the sample changes by6.90%;when the bending curvature is 0.2 cm^-1,which is close to the warhead,the average Seebeck coefficient of the sample is 63.78μV/℃.The coefficient variation is only 0.45%,which meets the application requirements.The prepared NiCr/NiCu flexible thin-film thermocouple was mounted on the surface of the xxx warhead and the target shooting test was carried out,and the transient temperature of the warhead surface was successfully obtained.The duration of the transient temperature rise process of the high-speed flight surface of the warhead is 41.15 ms,and the transient peak temperature is 388.3°C,which supports the development of the xxx warhead.