Signing of the ALE - DARE contract

DARE and Project Stratos have recently formalized their cooperation with Advanced Lightweight Engineering BV (ALE) with a sponsorship contract. The contract was signed last Friday afternoon (April the 12th 2013) at the ALE building in Delft.
DARE is looking forward to the cooperation with ALE on the design of pressure systems and composite structures for rocket technology. As ALE has a lot of experience in the design and analysis of structures made from composite materials, they can advise on how to best make use of the properties of these materials in the extreme conditions that rocketry requires.

Furthermore, ALE has a facility specifically made for the testing of tanks under pressure. DARE and Project Stratos have already made use of this in the past and will continue to use it under this cooperation.

With this cooperation a whole range of new possibilities lies open, DARE is already thinking about analysing composite structures for Stratos II together with ALE or designing composite tanks for a liquid rocket engine.
Tank test
The cooperation between ALE and DARE was immediately being put to practise in another tank test of the Stratos II propulsion team. After the test of the aluminium tank a few weeks back proved inconclusive on the tank strength, this test was needed to confirm that the tanks can hold for the full scale motor test at TNO in a few weeks.

Deformation of the test tank

In comparison to the previous prototype tank, this tank features bolts with a straight shaft to attach the bulkheads to the tank wall, where countersunk bolts were used previously.

Following the, by now standard, procedures for these types of tests, the tank was taken to a series of different pressure levels. Starting at a low 10 bars, just to check for leaks, the pressure was increased further up to 30 bar, 60 bar and then 90 bar. After each step the tank was inspected on deformations. At 60 bar, the designed operating pressure bulkhead was slightly shifted due to settling of the bulkhead in the construction, however no deformation could be found. At 90 bar a significant deformation had taken place on the wall near the top bulkhead, as predicted.

After this the tank was tested to destruction in order to validate the failure mode and burst pressure. The pressure was increased to 100 bar, which it sustained. After this the pressure was fully released and then increased rapidly to take it over this level. Now the tank failed at 94 bar in the intended failure mode of bulkhead shear-out. This indicates that the initial pressurization to 100 bar caused plastic deformation in the tank wall, weakening it.

The tank design has been approved for use during the upcoming ground test, as it can resist the intended operating pressure of 60 bar without problems and this tank design can be produced very consistently.