PSI - Issue 71

Sarath Chandran Nair S. et al. / Procedia Structural Integrity 71 (2025) 340–347

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FE analysis was done for room temperature and LN2 temperature conditions. Polyimide pipe and steel adaptor modelled using Shell181 element, and load is applied by link element. Mechanical properties of steel and polyimide, which are evaluated through a large number of tests, are used for analysis. Finite element analysis done for a typical polyimide pipe is explained here. The selected pipe has to undergo two deflection tests to simulate stress conditions at room temperature and LN2 temperature. Based on the FE analysis, load requirement and deflections to be simulated are predicted. Test and instrumentation plan for each polyimide pipe is finalised. Finite element model and loading scheme are shown in fig.3 (a) & (b).

b

c

a

Fig. 3: FE model and loading scheme for deflection test (a) Room Temperature; (b) LN2 temperature; (c) Split flange configuration Split flanges and closures for deflection test as shown in fig.3(c) are also designed based on the FE analysis as the pipelines are to be inducted into the cryogenic stage after the acceptance tests without any damage. This configuration is used for both room temperature and LN2 temperature tests. Stainless steel material is used for fabrication of split flanges and closures as end adaptors of polyimide pipes are also made of stainless steel. This will help in leak tightness under pressure and cryogenic temperature.

Displacement sensor

Pneumatic cylinder

Load cell

Test article

Fig. 4: Test set up for deflection test of polyimide pipe The test article – polyimide pipe is mounted in the test set up as shown in fig.4. The load is applied in steps with the help of a pneumatic cylinder. Load and deflections (Dx and Dy) correspond to each load step are monitored and reordered during the test. Loading will be continued until the required deflections are met as per the predictions. Unloading will be done in steps after achieving the required deflections. 7. Results and discussions Acceptance test of polyimide pipes used in the cryogenic stage for human space missions are done through deflection tests. Deflections to be achieved during the test are predicted through finite element analysis. Results of finite element analysis and deflections test for a typical polyimide pipe are discussed here. 7.1 Finite element analysis