Theoretical comparison of the thermo-mechanical fatigue characteristics of a tension rod and coil used as dewar supports

Abstract Support systems for dewars serve the dual purpose of holding the vessels together and providing a thermal insulation between the inner and the outer vessels. To decrease the heat inleak, the thermal length of the supports may be increased. The length of the support should be increased such that the support fits in the annular space between the vessels and gives the required mechanical strength. Coiled supports satisfy both the criterion. The supports experience thermal and mechanical fatigue due to the repeated filling and utilization of the cargo. This cyclic loading condition can cause mechanical fatigue failure and ductile to brittle transition of the material. While designing cryogenic dewars for long life, it is pertinent to ensure the longevity of the individual components. The life of a support depends on the number of cycles needed to cause the failure of the support. A model has been developed to predict the fatigue behaviour of support systems. Repeated loading condition was imposed to determine the life. The present work compares the fatigue characteristics of a coiled support with that of a tension rod under the same operating conditions.