Mechanical Tests

Mechanical tests

The space department of Air Liquide DTA is in charge of manufacturing the 3 thermal shields of the Herschel satellite. Each of these thermal shield is made of 3 adjacent parts : upper bulkhead, cylinder and lower bulkhead. The thermal shields (TS) assembly consists of three concentrically shells arranged like onion skins and provides the required thermal insulation of the He tanks, optical bench and instruments of the Herschel-extended payload module.

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To validate the design and the FEM calculation, two mechanical tests are required : a static test to verify the mechanical strength of supports under imposed load and/or displacements and a fatigue test at 77 K (Liquid N2 temperature) to verify the strength of a line under cyclic loading. The project being only in preliminary phase, the design isn’t frozen definitely. But, these tests have to be achieved rapidly. The description of these tests is provided in appendix for information and discussion. Due to hard planning constraints, the final test specification will have to be built conjointly to adapt the AIR LIQUIDE requests and the contractor test means.
These tests shall be programmed in beginning of June 2003.  The final test report shall be provided before the 1st of July 2003.


On the other hand, for reasons of hard constraints in geographical return out of France, we would like  you to achieve the whole of the following work: 
1. Realization / adaptation of the test bench  
2. Test specimen installation and instrumentation on the test bench 
3. Test plan redaction
4. Tests monitoring  with an AL supervision  engineer
5. Tests analysis and test report redaction
The manufacturing of the test specimen could be eventually included in your work if you are in measure to performed or to subcontract it. Then, definition drawings of the different elements would be provided to you. 
Thank you to answer us very quickly. 

Appendix 1: Supports static test

1) Scope 
This test consists in the mechanical strength verification of supports under static load and/or imposed displacements for which the direction can vary from a load case to the other. 

2) Test specimen

2-1) Case 1: Global test 

The test specimen, represented on figure 1.1 and 1.2, is made of: 

>3 aluminum 6061-T6 sheets curved on a 1691,6 mm radius assembled by the mean of bolted joints with riveted nuts. These sheets, having a thickness of  0,8 mm and forming a 90° portion of cylinder, simulate the Thermal Shields (TS) local stiffness. 

>2 kind of tested supports. These supports are manufactured with the same 0,8 mm thickness  aluminum sheet. The detail of these supports is indicated in figure 1.3 (the axis is not represented). These supports are fixed to the intermediate curved sheet by resistance spot welding.  Supports shall not be tested simultaneously and in case of any problem (local yielding), one supplementary support of each kind is foreseen to complete tests by turning over the specimen. 

2-1) Case 2: Local test 

The previous test allows to simulate the shields appropriate local stiffness but also the bolted joint flexibility to verify the supports mechanical strength. However, this test imposes a voluminous installation.
Therefore, it is envisaged for simplify the test, to achieve this static test by considering only the support spot welded on a plane sheet 200x200. This 0,8 mm thickness aluminum 6061-T6 sheet  is fixed on the test bench.

3) Test installation 

This test installation is the contractor responsibility. It adapts the specimen on the test bench. 
For the global test, a test installation proposition constituted by a rigid structure made of IPN or UPN beams is indicated on the figure 1.4. The test specimen would be directly screwed to the rigid structure. This structure is aimed at maintaining the specimen in place.  
For the load or imposed displacement application at the axis of the support, a jack (drivable in load and displacement) is to foresee.  The direction of this one will be able to be modified quickly between 2 tests to simulate the different load cases. On the other hand, a load deporting piece (mounted at the jack rod extremity) is to foresee for tests in the axial direction (according to Z) due to the limited accessibility of the axis (cf. support geometry). 
For the local test, the specimen would be screwed directly on a rigid plate. The loads application is identical to the global test.  
4) Load cases

The load cases to be considered are:

#1 (imposed displacement)

Axial (axis Z)
Maximum value (mm)
±5 mm
±5 mm

These displacements will probably be combined. So, the displacement direction shall be modified easily.

#2 (loads)

Axial (axis Z)
Maximum value (mm)
2000 N
1000 N


The lateral direction is the more soliciting direction between the X,Y,radial and perpendicular to the support axis directions. This direction will be specified later after FE prediction.

#3 (combination)

Combination of load cases # 1 and # 2 (TBC). ±

Appendix 1: Line fatigue test

1) Scope

This test consists in the mechanical strength verification of a line under alternated load at 77 K (Liquid Nitrogen temperature)

2) Test specimen

The test specimen is represented on the figure 2.1. It is constituted by a Ø12 line fixed at one extremity. The cyclic effort will be applied at the other extremity.
The exact direction of the effort will be specified later. Then, it's recommended to use the same load application installation as the previous static test.

3) Test installation

This installation is the contractor responsibility, shall adapt the specimen on the test bench and shall
maintain the line rigidly. Moreover, the line shall be continuously internal vented by LN2.

4) Load case

The exact value of the number of cycles to apply as well as static and dynamic effort values will be specified later.


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