Design Improvement And Analysis Of Internal Bonding Failure Of The Dew-type Thermocouple Probe In Harsh Environment

Cryogenic thermocouple is widely used in the temperature measurement of LH₂ and LO₂in the fuel tank of launch vehicle.In order to meet the response time requirements of space temperature measurement,the dew-type thermocouple probes is commonly used.But probe bonding failure occurred under the environment of high pressure and low temperature,resulting in leakage of LH₂,which is easy to lead significant security risks.For the bonding failure of the thermocouple probe,the influence of process on bonding behavior is analyzed,then the bonding morphology of different locations is investigated by SEM.When preload is applied to the cured probe,it could be found that there is a clear gap between the adhesive and the coupling rod,and the leakage channel is formed.In view of the bonding failure,a modification scheme is designed,which adds a rubber sealing structure.Firstly,the contact stress is calculated by FEA,then the influence of the length,number and shape of the rubber ring is considered.The results show that the effect of the number and shape of the rubber ring is very small,but the smaller of the rubber,the contact stress is more concentrated,the minimum contact stress is greater.Finally,it is determined that the scheme of the straight cylinder rubber ring and the corresponding preload is given.After the response time and the pressure test are qualified,the quality of temperature measurement the modified thermocouple should be evaluated.The uncertainty of measurement is an important index to evaluate the quality of thermocouple temperature measurement.In order to obtain more reliable results,the uncertainty of measurement of the thermocouple is evaluated by the uncertainty criterion and Monte Carlo method.Both of them meet the requirements of the verification regulation,which shows that the product could meet the requirements of space temperature measurement.